— Sa ane ene . PAE RNA Fag the Mat rare eae os 3 soete! =A 14] rod i al ' ' : ' u : - 1 va BUM en nln OF THE DEPARTMENT OF GEOLOGY OF THE UNIVERSITY OF CALIFORNIA VOLUME 2 ANDREW C. LAWSON, Editor 20eL000, ay ee F C ane Oe ; rs , Geology of Point Sal BY . ‘ HAROLD: ~W. FAIRBANKS Fre a % on Q 4 pes oS gant i <*04,, Ay My oat LZ = — ip7 Sy Ze mi SVS ges le Sass Ne 1S) eS 7 «\ \ (OY 4 SSS IE id BERKELEY > PUBLISHED BY THE UNIVERSITY id Ga NAY, 1896. ANDREW C. LAWSON, Editor PRICE, 65 CENTS WAR HON ZL fy O&y I UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology Vol. 2, No. 1, pp. 1-92, Pls. 1, 2. ANDREW C. LAWSON, Editor THE GEOLOGY. OF POINT SAL. BY HarROLpD W. FAIRBANKS CONTENTS. MELO GIG Obert Sos ssce shssctnn sat este action sense nana, Galttae ve Se ae LS ee, pyres ree a hee “as SG Siang FIGURE 5.—Inclusions of gabbro in serpentine on the contact. the cliffs from that forming the arms which extend out into the water. Its relation to the gabbro is an interesting one, but difficult to understand. The following sketch from a photograph (Fig. 5) shows the manner in which the gabbro is inclosed in the serpentine. Both are perfectly massive, no appearance of shearing being notice- able in this vicinity. They appear mixed on their edges in the most intricate manner. The stringy and ragged edges of the gab- bro, the mutual penetrations and apparent inclusions of one in the other near their line of contact, make it appear as if both were more or less viscous at the time of the intrusion of the picrite. It does not 54 University of California. [Vor. 2. seem possible that a rigid body could be penetrated as the gabbro has been and yet retain its solid condition. At the spot where the photograph was taken, it seems as if the gabbro must have been the more fluid of the two, but in other places a short distance away the reverse is certainly the case. Although in general the contact is sharp, there is sometimes a slight blending with long narrow arms of the gabbro projecting into the serpentine. One important fact, which would lead to the supposition that the phenomenon is due to an invasion of the gabbro by the picrite is, that almost everywhere near the contact, the latter contains more or less feld- spar in aggregates which present to the eye a slight resemblance to poikilitic crystals, often drawn out in rude parallelism. An inclu- sion of a boulder-like mass of gabbro in the serpentine was noted which has a peculiar character. It is about two feet in diameter, and shows concentric bands of feldspar arranged on three sides near the periphery. The simplest explanation of the inclusions in the serpentine, and probably the true one, is that of absorption of the gabbro by the more magnesian magma. The latter must have retained its heat for some time, and literally eaten into the gabbro, the irregular contact being due to fissures along which résorption would proceed faster. A body of gabbro and related rocks lying south of the west- ern end of the serpentine, and forming one of the projecting points, offers a most interesting field for the study of many different intrusions of varying character. A part of it consists of gneissoid and finely banded troctolite. In other portions there is a confused, mixture of gabbro of different kinds. Patches of a banded gabbro appear inclosed in a somewhat similar rock, whose banding makes an angle with that of the inclusion, the boundaries not being strongly marked, as if a partial fusion of the latter had taken place. Across one end of the area, a dark, fine-grained norite-gabbro has been intruded obliquely to the banding of the larger mass, while along the contact there is a differentiated layer of almost pure feldspar. Dikes are seen which vary in different portions, as well as those which are uniform and distinct. Among the coarsely crystalline rocks the troctolite is prominent. The darker, finer-grained dikes, including gabbros, norite-gabbros with or without olivine, and nN FAIRBANKS. } Geology of Point Sal. 55 picrite, show every variation between the troctolite and the non- feldspathic peridotite. Between this point and the Chute at Point Morrito, the different facies of the feldspathic and non-feldspathic rocks appear in such variety, and show such complex intrusive rela- tions, that it is difficult to give an intelligible description. The serpentinized picrite, which lies between these complex bodies of gabbroitic rocks and the mainland, continues toward the southeast until it narrows and passes into the cliffs. At the last spot where it was observed it forms a dike-like intrusion across the banding of the gabbro, and both are in turn cut by a narrow dike of norite- gabbro. The confused mixture of the serpentine with the gabbro, which has already been described, is characteristic of the contact at different spots. There are many illustrations of the inclusion of the gabbro inthe serpentine. It is shown clearly that the gabbro was fully consolidated and subsequently broken up by the basic magma which ate its way in resorbing the solid rock, until it left long arms of nearly isolated or wholly inclosed fragments. Dur- ing this process little movement seems to have taken place, and since consolidation none at all. Inclusions of gabbro, often several feet long, show the same’ uniform banding as that adjoining the ser- pentine. The banding may be parallel to the long diameter of the inclusions, or oblique, and when several fragments appear near together, it is approximately parallel in them all. The gabbro forming the last rocky projection west of Point Morrito has also a varied character. Much of it is finely banded, the bands extending for many feet in perfectly straight lines. An interesting inclusion of dark hypersthene gabbro, having an ellipti- cal shape, occurs inclesed in a coarser rock of the same character. The bands of the inclosing rock are cut off by the inclusion. A dike of peridotite, cutting the gabbro and gneissoid troctolite, con- tains inclusions of the adjoining rocks. These vary in size from very small grains up to elliptical masses four inches in diameter, and are so strung along inthe dike that it presents a distinctly banded structure. Inaddition, the dike itself is banded with streaks of a lighter colored feldspathic peridotite. Another dike of serpen- tine 12 feet wide contains large masses of lighter colored feldspathic material, apparently representing fragments of gabbro partially 5 . 56 University of California. [Vor. 2. absorbed. Their long diameters lie parallel to the walls of the dike. Traversing both the serpentine and gabbro are fine-grained dikes a few inches to a foot wide, which contain feldspar, olivine, hypersthene, augite and magnetite. Along the western side of Point Morrito the peridotite has been highly differentiated petrographically, and intruded by later dikes, producing a great complication. The cliffs,as far east as the Chute, consist of rock often coarsely crystallized, the predominant compo- nent in different spots being either olivine, augite, or hypersthene, with occasionally considerable feldspar. This mass is perhaps 1,000 feet long, and has an irregular outline. It extends to the water, and nearly to the northern side of the complex on the hill above the point; and, although the exposures back from the ocean are poor, it has apparently been forced into the gabbro, terminating on the edges in a series of dikes, and inclosing masses of the gabbro. The relations are the same as those of the serpentinized picrite a little farther west, both bodies undoubtedly belonging to the same intru- sive, This peridotite magma presents great differences in different parts. At the western end it is a dark, compact rock, containing disseminated feldspar, and forming a picrite. In the direction of the main body it becomes coarser, with less feldspar and abundant diallage. Between it and the gabbro occurs a dike of intermediate composition. Inthe high cliffs at Point Morrito the olivinitic facies is mixed with the pyroxenic in the most confused manner. Over portions of this area the olivine and green diallage appear in about equal proportions, forming wehrlite; in others each component ap- pears segregated by itself to form pure masses of olivine or diallage. These segregations have an irregular form, each extending out in shreddy projections into the other, or the one forming well-defined veins in the other. There is no banding or system in the relation between the two. This interesting condition of things is shown for several hundred feet in the middle and upper portion of the cliffs. On the west side of the Point are the largest areas of almost pure bright green diallage, the crystals reaching one to two inches in length. Where the olivine is abundant, that component has the appearance of forming a paste in which the pyroxene rests, or the FAIRBANKS. ] Geology of Point Sal. 57 latter penetrates the olivine in veins. Where the pyroxene is in excess, the reverse is the case. In the fresh specimen the olivine is black, but it always appears reddish on weathered surfaces. Towards the water’s edge this olivine-pyroxene rock is replaced by a banded feldspathic one, the bands running parallel with the coast, and dipping towards the land. It appears first as dikes in the olivine and pyroxene, while near the water’s edge the latter are en- tirely replaced. The different bands of this more feldspathic magma do not have the appearance of being separate dikes. Although in places the division lines are strongly marked, yet in general there is a more or less blending of the more feldspathic bands into those less feldspathic. These bands might be explained by movement in a heterogeneous magma which rose through the wehrlite before the complete solidification of the latter. At the western end of the wehrlite, where it is the most coarsely crystallized, there is a body of saxonite having a width of at least 4o feet in the upper part of the cliffs. It has an exposed length of several hundred feet, extend- ing up the hill towards the gate in the road. It is generally a dark brownish rock, in which appear large crystals of hypersthene. It blends on the one hand into a facies with no olivine, and on the other into the olivine-pyroxene rocks. On the lower edge of this area there is a segregated mass of hypersthene and feldspar, which, with perfect correctness, might be called norite. A varying amount of feldspar is characteristic of the whole hypersthene area. A vein similar in manner of formation to those in the gabbro traverses the feldspar-hypersthene rock. It consists of those two components in large crystals, the hypersthene reaching a diameter of one to one anda half inches. No sharp lines could be drawn between the picrite on the west and the wehrlite, saxonite, and pyroxenite on the east. The hypersthene replaces more or less completely the augite of the picrite to form the saxonite, but is always associated with some feldspar. The small area of hypersthene feldspar rock is inclosed on all sides by the peridotite, and must be looked upon as a segregation from the magma. Dikes and veins of every conceivable variation between the olivine rock and the feldspathic ones, pene- trate this complex between Point Morrito and the gabbro on the west. Many of these are banded and some are coarsely crystallized, 58 University of California. [Vot. 2. like those in the gabbro. The character of the rock through which the so-called veins pass, has no effect upon their mineralogical com- position. It is very difficult to tell which are true dikes and which are veins of segregation. In this vicinity are the most striking and sudden changes in texture, structure, and composition. Portions of the same eruptive mass show as great variations in a very short distance as might be expected from wholly distinct masses. The wehrlite passes up the hill back of Point Morrito, constitut- ing much of that promontory, but the outcrops are poor. South of the hill and along the coast east of the Chute the formation changes considerably. The wehrlite is replaced by a dark apha- nitic serpentine (dunite), which is traversed by many branching irregular dikes of diabase. ; The first cafion east of the Chute gives a clean section across the complex, which is here about 1,000 feet wide. The upper por- tion consists of gabbro for several hundred feet, with a small amount of diabase. There seem to be different intrusions here, but their relations are not plain. Below these is a belt of altered dunite extending to the ocean. It has a uniform appearance, except near the sea, where it contains a small amount of feldspar and enstatite. Just above the water it is intersected by many narrow dikes of diabasic character, and at one spot by a dike of wehrlite. East of the spot where this gulch enters the ocean, a prominent dike of diabase runs parallel with the cliffs for a quarter ofa mile. The clean cut contacts with the serpentine show that it is intrusive, a fact which is also corroborated by the character of the dike. It is fine and almost porcelain-like on the edges and coarser in the middle. It adheres so firmly to the serpentine that, instead of parting at the real junction, the separation is about two inches within the serpentine. In addition to the large dike, which is fre- quently 12 feet in diameter, there are numerous smaller ones. The serpentine here is generally massive, showing lamination only in spots. The exceedingly irregular and bunchy nature of these dikes explains how it is that when shearing has affected the serpen- tine, the dikes are broken up into boulder-like masses, which, in the most of the serpentine areas in the Coast Ranges, are so difficult of explanation. Pete FaiRBANKS. | Geology of Point Sal. 5¢ fs ) In addition to the dikes which are of later date than the serpen- tine, there appear at numerous spots along the ocean bands and streaks of lighter color. They differ from the serpentine in contain- ing augite and feldspar in addition to olivine, and might be termed picrites, although some are almost gabbroitic in appearance. They are not generally sharply differentiated from the serpentine, the dark bands passing into it with apparently little change. These feldspathic bands are sometimes intersected by dikes, two to three inches in thickness, which do not differ greatly in appearance but contain abundant hypersthene. The steep southern slope of the Lion’s Head consists of a rock quite similar to that forming the higher part of Point Morrito, namely, diallage and olivine, the former frequently in large green crystals. “ The section given along the first creek east of the Lion’s Head is quite similar to that west. On the northern side of the complex there is first 500 to 600 feet of diabase and gabbro. The extreme edge is a dark, fine-grained diabase, containing coarse, irreg- ular veins. The veins recur occasionally until the bridge is reached at the mouth of the cafion, where a dark, aphanitic serpentine replaces all the feldspathic rock. In the serpentine near the con- tact are bodies of coarse hornblende gabbro, while narrow dikes of serpentine intrude the feldspathic rock. Toward the southern edge the serpentine becomes coarser, with prominent pyroxene crystals. A little above the beach there appears in it, as shown in the sides of a shallow ravine, a broken dike of gabbro. The serpentine near it is greatly sheared, while the banding of the gabbro is apparently diagonal to the course of the dike. From a point opposite the Lion’s Head the serpentines extend only a half mile southward before disappearing beneath the Miocene. The different rock types which appear here are numerous and inter- esting. Beneath the Head where the road comes nearest to the cliffs there are some irregular dikes of diabase, which have broken through the serpentine and caught up fragments of it as shown in the annexed sketch, taken from a photograph (Fig. 6). The cliff section cuts diagonally across the serpentine to its southern side. Following along the shore, from the point where the large dike occurs, there are many smali ones to be seen. These split up into 60 University of California. [Vo. 2. branches two to three inches in thickness, from which branch again still smaller ones perpendicularly, thinning out finally to knife edges. The large dikes and many of the smaller ones con- tain inclusions of serpentine. These inclusions are frequently Ficure 6.—Irregular dike of diabase inclosing fragments of serpentine. drawn out in long, shreddy wisps. In order for these to assume the form shown here, it would seem necessary for the serpentine to have been in a somewhat plastic condition. Occasional dikes of hornblende gabbro contain rounded and partially absorbed nodules of serpentine. In one instance these inclusions appeared surrounded by a green border shading into the gabbro. In one case the inclu- sions of serpentine in a gabbro dike are sharply angular in outline (Fig. 7). The dark serpentine which forms the most of the coast line from the Chute southeastward is interseeted in many places by veins one to two inches wide. These consist either of feldspar and coarse crystals of green pyroxene or wholly of pyroxene. In the —— FAIRBANKS. ] Geology of Point Sal. 61 FIGuRE 7.—In the center are shown angular fragments of serpentine inclosed in a gabbro dike. vicinity of the greatest development of the diabase dikes considera- ble movement has taken place, and veins of pectolite fill the seams. They are most abundant in the diabase and along the contact. South of the Head a dike of olivine-rich gabbro occurs in the ser- pentine. Near the southern end of the cliffs there is an interesting series of gabbroitic dikes. The following section is shown: First a gabbro dike 200 to 300 feet wide, then a few feet of dark, sheared serpentine containing nodular masses of a hypersthene gabbro, probably a dike broken up by movement; after this an irregular dike of gabbro two to five feet wide, followed by another of picrite, and that by a dike of troctolite; serpentine at last terminates the series, disappearing beneath the débris. At several spots there were noted dikes intermediate in character between the gabbros and peridotites, which were later than the peridotite, but there are good examples of distinctly gabbroitic dikes intrusive in the dunite. The last and deepest of the cafions which have been eroded across this eruptive complex is that leading up to the dairy and the old gypsum mines. A section is shown here quite similar to that farther west. At the northern side there are diabasic dikes of dif- 62 University of California. (Vor. 2. ferent degrees of coarseness, and a small amount of gabbro and hypersthene gabbro. Below this the dark serpentine extends until covered by the Miocene. Towards the southeast the belt widens to nearly a quarter of a mile. This portion is comparatively simple; for, although there are deep cuts to expose the rock, the greater portion consists of the compact altered dunite, with a comparatively narrow strip, perhaps less than 200 feet, of fine-grained diabase. But little signs of shearing are seen in this portion. This, the larg- est body of altered peridotite, judging from its massive character, does not bear out the view that is frequently advanced that hydra- tion is the cause of the broken, laminated, or clayey character of many serpentines. Wherever the Point Sal serpentines have lost their massive character, it seems to be due in great measure, if not entirely, to shearing brought about by earth movements. The most disturbed portion is along the coast where it has been intruded by dikes which are generally nearly parallel to the long diameter of the eruptive mass asa whole. This direction corresponds to the lines of movement and faulting in the Coast Ranges. Microscopic Petrography.—In the field the gabbros are generally distinctly marked off from the peridotites, although there are facies of each almost identical, besides independent bodies of intermediate composition. The following classification is made purely for the purposes of description, and is not meant to convey the impression that there are any distinct types clearly set off from the rest. In fact, there are all conceivable mineralogical transitions between that consisting almost wholly of feldspar and the magnesian or olivine rock. Three main divisions may be made: (Ij The olivine-free feld- spathic rocks, (II) the olivine-bearing feldspathic rocks, (III) peri- dotite and pyroxenite. 1 Feldspar. Anorthosite. Feldspar, hornblende. Hornblende diabase. Feldspar, hornblende, quartz. Ophitic quartz diorite. Feldspar, hornblende, hypersthene. . Hypersthene diabase. Feldspar,augite (with or without hornblende). Diabase or gabbro. Feldspar, augite, hypersthene (with or with- out hornblende). : Norite-gabbro. Feldspar, hypersthene. Norite. = (FAIRBANKS. | Geology of Point Sal. 63 II. Feldspar, olivine, augite (with or without hornblende). Olivine gabbro. Feldspar, olivine, augite, hypersthene (with or without hornblende). Olivine norite-gabbro, Feldspar, olivine, hypersthene. Olivine norite. | Feldspar, olivine. Troctolite. LED Olivine, diallage, hypersthene, little feldspar. Feldspathic lherzolite. Olivine, diallage, hornblende, little feldspar. Hornblende picrite. Olivine, hypersthene, little feldspar. Feldspathic saxonite. Olivine, augite or diallage, little feldspar. Picrite. Olivine, enstatite, diallage. Lherzolite. Olivine, hornblende. Olivine, diallage. Wherlite. Olivine. Dunite. Diallage. Pyroxenite. The feldspar of these rocks, with rare exceptions, all belongs to anorthite. One exception is that of feldspar intergrown with quartz in veins in the serpentine which seems to lie between labradorite and albite. Feldspar approximating labradorite is found in several of the diabasic dikes, but in all the facies of the gabbro it undoubt- edly belongs at the extreme basic end of the series. Large extinc- tion angles were noted, while the specific gravity ranges between 2.73 and 2.758. It is generally very fresh and free from inclusions. In the rocks rich in olivine, alteration has begun, and where the feld- spar forms but a small portion of the rock, as in certain facies of the peridotites, it is completely altered to a white, opaque, and com- pletely amorphous substance. In none of the specimens did apatite appear as inclusions, either in the feldspar or any other of the com- ponents. Twinning was noted in the feldspars on the carlsbad, albite, and pericline laws, that of the albite prevailing. The monoclinic pyroxene has a uniform character, aside from secondary changes, in all parts of the eruptive mass. In the hand specimen it appears a deep green color, but in thin section under the microscope it is non-pleochroic and almost colorless. In many 64 University of California. [Vor. 2. portions it is exceedingly fresh, but in the coarser rocks and perido- tites it shows all stages of the alteration to diallage. The alteration begins by the creation through the center of the crystal of fine cleavage planes parallel to the orthopinacoid. Associated with these parallel cracks in the center of the crystal are long rectangular or spindle-shaped alteration products, which polarize brightly when the remainder of the crystal is dark. Slender magnetite rods are sometimes developed in the alteration. Inclusions of hornblende are quite common, being arranged either irregularly or along the cleavage planes. Occasionally the augite shows an approximation to an idiomorphic form, but in general it is allotriomorphic. The rhombic pyroxene present is chiefly hypersthene, a colorless non-pleochroic enstatite being seen in only a few instances. The hypersthene is remarkably widespread, occurring in nearly all facies of the rock except some of.the purely non-feldspathic ones. Its - presence seems to have no relation to the presence or absence of olivine. It is strongly pleochroic, showing the usual colors, a= red, b=yellow, ¢=green. Sections parallel to the macropinacoid are often devoid of pleochroism, remaining green in all positions, and show the emergence of an optic axis. The axial angle is small, for both axes appear in the field in convergent light. The specific grav- ity, which is 3.315, is rather low for this mineral, and shows that it is not rich in iron. Asa rule the crystals are exceedingly fresh and free from inclusions, which are so characteristic of hypersthene. No schillerization was seen, but in those individuals which had become slightly affected by alteration there has been produced a system of fine parallel cracks. Hornblende is fully as widely distributed through the different facies of the rock as hypersthene, save that it is less common in the peridotites. It generally plays a less important rdle than the hyper- sthene, except in the ophite diorites. In the dikes of diabasic structure it has clearly replaced the pyroxene in some cases, while in others it must be considered primary. In the gabbros it some- times occurs in independent individuals, but more commonly as broken or discontinuous rims about the augite grains, and occasion- ally about the olivine. It is quite strongly pleochroic, giving brownish, greenish brown, and pale yellow tints. It is what is termed basaltic hornblende. FAIRBANKS. ] Geology of Point Sal. 65 Olivine is almost universally present in the gabbros and perido- tites, but generally absent from the diabasic dikes. It is in a fairly fresh condition in the feldspathic rocks, but appears in all stages of alteration in the peridotites, until the extreme is reached in the dunites, where in some cases its former presence is recognized only by the mesh structure. It never possesses idiomorphic boundaries, but has the form of rounded grains or irregular aggregates of indi- viduals differently oriented. The rocks asa whole are remarkable for the small amount of iron ores present. Magnetiteis absent from the normal gabbro and peridotite, and occurs in abundance only in the narrow dikes which appear to have been among the latest of the intrusions. The peri- dotites are remarkable also for their small amount of chromite and picotite. In one slide only do there appear a few reddish grains, which are probably referable to one of these minerals, Having given now an outline of the characters of the rock- forming minerals, a brief description will be added of the various rock facies. The blending of one variety into another adds to the complexity of the subject, but typical examples of the different facies already given will aid in understanding them. The anorthosites, those rocks poor in the ferro-magnesian sili- cates, occur in the gabbro in the form of bands occasionally reach- ing a width of six inches. Bands one to two feet wide, which appear more like veins, occur in the massive gabbro. There are also ill-defined areas in which the dark silicates are sparingly repre- sented. In different parts of this facies appear small amounts of olivine, augite, and brown hornblende. In one vein the feldspars appear most curiously dovetailed into each other, and many indi- viduals, particularly those not showing twinning, present a sort of zonal structure with a jagged outer rim extinguishing at a different angle from a similarly jagged interior. The dikes possessing an ophitic structure range from true dia- bases to quartz-diorite. A dike of the latter was noted intrusive in the gabbro. It is four feet wide, dark, and very fine grained on the edges. Judging from the extinction angles, the feldspars evidently belong in the more acid portion of the labradorite series. They have well-marked zonal structure. The hornblende is without any 66 University of California. [Vor. 2. doubt primary, showing characteristic basal sections and a pale greenish brown color. Quartz occurs filling interstices between the other components, being the last to separate. Magnetite is quite abundant in skeleton crystals. The question arises in regard to the proper designation for a rock of this kind. A silica determination gave 66 per cent, which is rather acid, even for a diorite, as the term is used. The distinc- tion which Brogger* has proposed seems a very good one, that is, to confine the use of the term diorite to the medium acid abyssal rocks of granitic structure, while the term diabase is to be used for the hypabyssal rocks. These to be farther divided into medium and basic rocks corresponding to the deep-seated ones diorite and gab- bro. He considers the classification according to the ruling dark constituent of very little value. In accordance with this the rock will be designated simply an ophitic quartz-diorite. A new name, it would seem, must ultimately be adopted for medium acid rocks of diabasic structure. Another dike farther east contains greenish brown hornblende in granules and broad plates. The latter are thickly dotted in a poikilitic manner with exceedingly minute feldspar laths. The greater number of the diabase dikes east of the Lion’s Head contain a greenish, shreddy hornblende and lath feldspars. The former often incloses cores of granular augite, showing that a part of the hornblende at least has been derived from augite. The primary nature of a part of the hornblende is evident from the form of the basal sections and the manner in which it incloses the feldspars, a similar structure not having been seen in the case of the augite. As a general thing, the feldspar of these rocks is more decomposed than in any of the other feldspathic rocks. A rather interesting dike of diabase occurs intrusive in the ser- pentine south of the Head. It is a fine-grained rock, containing poikilitic crystals of primary brown hornblende. In these crystals are numerous inclusions of feldspar, augite, and hypersthene. The hornblende and augite are slightly more abundant than the hyper- sthene. The feldspar laths probably belong to anorthite. Small * Die Eruptionsfolge der Triadischen Eruptivegesteine in Sudtyrol. FAIRBANKS. ] Geology of Point Sal. 67 grains of magnetite are abundant. All the minerals of the rock are fresh. There area few large crystals of augite showing the diallagic cleavage. A fine-grained dike, three inches wide, is intrusive in the gabbro and peridotite west of Point Morrito. A thin section shows horn- blende, augite, hypersthene, and feldspar, the minerals all being in a fresh condition. A distinct banding is shown, due to the segrega- tion of a part of the hornblende. The four constituents are present in about equal proportion, while magnetite is abundantly scattered through the rock. Although the most of the constituents are granular, there is a tendency to the elongation of some of the feldspars and their arrangement with their long diameters parallel to the walls of the dike. No other instance of a parallelism of this kind appeared. Ina dike of crushed serpentine south of the Head occur nodules of a dark, fine-grained rock, with serpentine adhering to one side. They appear to belong to a dike broken up in the movement which brought about the crushing of the serpentine. The composition of this rock is the same as the last. There is a slight tendency toward the arrangement of the constituents in lines. This is particularly noticeable in the case of the magnetite, which appears in bands made up of scattered grains. The combination of minerals just described is not a common one for the coarse gabbro, olivine being so widely distributed through that rock that but few specimens were obtained which did not contain it. The combination of feldspar and augite or diallage is also uncommon in the coarser rocks. Norite-gabbros are not abundant, though several dikes of this rock occur. Hornblende almost always is present in these dikes, which are most numerous in the gabbro-peridotite area west of Point Morrito. A small dike only a few inches wide, and almost apha- nitic in the hand specimen, might be cited asa characteristic example. Under the microscope it is seen to possess a typically holocrystal- line granular structure. The components, feldspar, augite, and hypersthene, are perfectly fresh and present in about equal propor- tions. Magnetite dust is scattered thickly through the slide. The typical norite, free from augite, was found to occur only as 68 University of California. [VoL. 2. a facies of the complex peridotite area at Point Morrito. Here isa small body of rock, a segregation from the magnesian magma which surrounds it on all sides. It consists of feldspar and hypersthene in varying proportions, and, occasionally, small grains of magnetite. The constituents are fresh and free from interpositions. With decrease of feldspar there are transitions to a rock consisting almost wholly of hypersthene, and with the addition of augite and olivine gradations to the more common peridotite. A portion of this norite is very coarsely crystallized, the crystals reaching a diameter of one and a half inches. The typical olivine-gabbro is an abundant rock, and is represented in the collection by many slides. It often contains a little hyper- sthene and shreds of brown hornblende. The olivine occurs in irregular-shaped aggregates, and in those rocks which are banded it is strung out in more or less connected patches. The beginning of alteration is usually apparent in a yellowish border and an inter- secting network of cracks. Although the first mineral to separate out, it is never idiomorphic. A number of inclusions of olivine in augite were observed where the grains of the former had a very perfect elliptical outline. One of the most striking phenomena associated with these olivine-bearing rocks is the system of radiating cracks which extend out into the feldspar from the olivine aggre- gates. These cracks are grouped in parallel or radial bunches, diverging from the projecting points of the olivine aggregate and extending through the intervening feldspar, to the adjoining aggre- gates of the same mineral. The extent to which this is developed, even in those rocks in which alteration is but slightly apparent in the olivine, is very remarkable. In the coarser rocks, and in the larger individuals of augite.in most specimens, there is observed the beginning of alteration indi- cated by the development of an assemblage of fine parallel cleavage cracks and polarizing interpositions. In the banded varieties, the olivine is segregated in layers; other layers consist of olivine and augite, between which are the feldspathic bands, containing some augite, but free from olivine. The fresh condition of the augite, which in many sections has associated with it partial rims or shreds of brown hornblende, make it fairly certain that the latter is original, and was the last constituent to crystallize out. aks Aa ——" FAIRBANKS. | Geology of Point Sal. 69 With the decrease of augite we reach the type of rock to which he term “troctolite” has been given (German, Forellenstein). This rock sometimes occurs as facies of the normal gabbro, and some- times as homogeneous independent dikes. A dike of this kind appears intrusive in the serpentine south of the Lion’s Head. The greater portion of the troctolite is found in the near vicinity of the peridotite area west of Point Morrito. While it occurs here well- defined from ,the true gabbros, yet it is genetically connected with them rather than with the peridotite. The rock is here remark- ably gneissoid, owing to the arrangement of the olivine granules in long, platy aggregates. It is an interesting fact that the olivine grains never occur alone, except as inclusions in the other constit- uents. The feldspars are invariably allotriomorphic. The rocks are rarely free from small amounts of augite and hornblende. Magnetite is absent from all the specimens examined. Olivine norite-gabbro is quite common, occurring almost always as dikes in the complicated area west of Point Morrito. Some of these have a subordinate amount of feldspar, and might perhaps be considered as transitions to the peridotite. South of the Lion’s Head a dike of this composition was seen intrusive in a peridotitic rock. The latter consists of augite, olivine, feldspar, and horn- blende, the two last components in small amount, while magnetite is abundant. The dike is about two inches wide, but possesses a typical granular structure with the following composition: augite, hypersthene, feldspar, olivine, and a small amount of magnetite. The constituents of the two rocks interlock along the contact in ‘such a manner as to lead to the view that the older was not fully ‘consolidated at the time of intrusion. A hornblende-bearing facies of this type is illustrated by an interesting specimen from the cafion below the dairy. It is some- what more coarsely crystalline than the others, and contains an abundance of granules and irregular plates of a pale yellowish brown hornblende with weak pleochroism. It is intergrown in several cases in a granophyric manner with the augite. Some of the hornblende has a poikilitic habit, with inclusions of the other constituents. Several large irregular crystals of olivine are pres- ent, and one section of twinned augite approximately idiomorphic. There is in addition a very little magnetite. 70 University of California. [VoL. 2. Observation both in the field and with the microscope confirms. the fact of a continuous petrographic series between the strictly feldspathic and the non-feldspathic portions. Feldspar is widely distributed in rocks which must really be classed with the perido- tites under our present nomenclature. As an example of this may be cited a rock consisting of olivine, hypersthene, and feldspar. The olivine forms about half of the rock, while the remainder is. equally divided between the other two. The olivine is largely decomposed toa reddish brown mesh with fresh cores, while the comparatively fresh feldspar is distributed through it in small crystals. The hypersthene occurs in relatively large, almost por- phyritic individuals, also quite fresh and free from interpositions. An examination of the literature upon serpentines and perido- tites shows that much confusion exists. The usage is so different by different authors that it becomes very difficult to reduce to any system of classification the great variety of these rocks in the area under consideration. Much of the peridotite is quite fresh, the greatest amount of alteration of course being confined to that rich- est in olivine. The augite may be either normal or show all stages of change to diallage, the larger crystals being generally diallagic, while the smaller are normal augite. As many authors have based the classification on the character of the monoclinic pyroxene, whether augite or diallage, it adds much to the difficulty of making a Classification which shall conform to usage. Under the head of lherzolite are grouped those rocks which con- tain olivine, augite or diallage, hypersthene or enstatite, and often a small amount of feldspar. These rocks are chiefly confined to Point Morrito, where they are intimately associated with non- feldspathic peridotites. Except for the occasional patches of feld- spar, hypersthene is the most striking constituent in the hand spec- imen, appearing in porphyritic crystals one-fourth to one-half inch in diameter, imbedded in a base of olivine and minute feldspars. Under the microscope the olivine appears to have decomposed to an almost opaque network of magnetite and reddish oxides, scat- tered through which are fresh olivine cores. The feldspar is com- paratively fresh but seamed. The larger individuals of hypersthene show no crystal boundaries, but are fresh, and without interposi- FAIRBANKS. ] Geology of Point Sal. 71 tions. The pleochroism is rather weak. Crystals of diallage are occasionally present. Some sections contain no diallage,and might be termed saxonite. Intimately related geologically to the hyper- sthene peridotite is a large area consisting of diallage and olivine with or without feldspar. Where the olivine is greatly in excess, and much decomposed, the feldspar has been changed to a white, translucent but isotropic substance. In some facies in which the diallage is in excess, the olivine forms a sort of cementing paste in which it is imbedded. The pyroxenes show no true crystal outlines; yet there is often a rude approximation to them. With an increase of olivine there is an increased amount of alteration noticeable, the olivine being reduced to a brownish serpentine, with here and there fresh cores. The pyroxenes appear fissured and permeated with seams of serpentine. An interesting section was obtained from the southern slope of the Lion’s Head. It consists of partly serpentinized olivine and diallage in nearly equal proportions. The apparently separate individuals of the latter are almost similarly oriented, as shown by the extinction angles. An examination of the hand specimen showed the existence of lustrous mottled surfaces an inch or more in diameter. This indicates that the extinction phenomenon is pro- duced by large poikilitic crystals of diallage. The slight discord- ance in orientation appearing in the section may be accounted for by strain and movement brought about by the hydration of the olivine matrix. It is rather difficult to distinguish the wehrlites from the picrites unless the feldspar present in the latter be made the basis. The fine- grained peridotites west of Point Morrito containing feldspar are not clearly set off from the wehrlites through any peculiarity of the pyroxene. In the picrites proper the pyroxenic constituent is sup- posed to be augite, but in the rocks mentioned it is more nearly diallage than augite, the smaller individuals still retaining their augitic character, while the larger are undoubtedly diallage. Thin sections of these rocks show the olivine to be in an advanced stage of alteration. It is represented by an almost colorless or grayish aggregate of felted serpentine shreds, among which appear occa- sionally grains of altered feldspar (isotropic) and a pale colored augite or diallage. 6 72 University of California. [Vot. 2. The lherzolite type with enstatite as the rhombic pyroxene is rather sparingly represented. A thin section from the dark serpen- tine east of the Chute contained a serpentinized olivine in excess, with here and there irregular grains of a colorless rhombic pyroxene, and still more rarely those of a monoclinic pyroxene. Another spec- imen obtained near the Lion’s Head contained, in addition to the minerals in the last, allotriomorphic masses of reddish brown horn- blende. The latter appears to be the freshest of any of the con- stituents. The pyroxenite occurs at Point Morrito as segregations in the wherlite. It is seldom wholly free from olivine, and occurs in irreg- ular patches of considerable size imbedded in a matrix consisting chiefly of olivine. The dunite is represented by the dark homogeneous serpentine. It forms by far the larger part of the peridotite area, being mainly developed between the Chute and the eastern end of the complex. Under the microscope its derivation from olivine appears clear. In specimens in which the alteration is not complete there are scat- tered spots of small size of a brilliantly polarizing, highly refract- ing mineral. These grains are inclosed in a mesh of interlacing fibers of serpentine. Numbers: of them near together extinguish simultaneously, showing them to be portions of a single crystal. With the analyzer removed the reticulated mesh structure, which is considered characteristic of olivine, is apparent throughout the whole slide with the exception of the clear spots. In some slides no olivine remains. A remarkably banded rock occurs near the Head. This con- tains hornblende, augite, olivine, hypersthene, and feldspar. Owing to the small proportion of feldspar it might be considered as belong- ing between the two main groups. The large irregular plates of yellowish brown hornblende contain inclusions of all the other con- stituents. The diallagic augite is gathered in bands free from the other components, the individuals being arranged with their vertical axes approximately normal to the edges of the band. The petrography of the “segregated veins” or dikes which appear in different portions is interesting. Without doubt these occurrences can be divided into two classes, one of which might be FAIRBANKS. ] Geology of Point Sal. 73 termed contemporaneous segregations, which, on account of a pro- longed period of solidification, took on their coarsely crystalline character, and the other true dikes of later age than the rocks which they intersect. It is not always possible, however, to draw the line between them. The segregated veins in the gabbro do not differ much, or even any, from the average composition of that rock. They consist of feldspar, diallage, and olivine. The two former in large individuals, the last in aggregates of grains as in the normal rock. Veins of essentially the same composition appear also in the peridotite, but in the hypersthene area there are very coarse vein- like masses of hypersthene and feldspar which do not appear else- where. Veins with black hornblende appear at one spot west of Point Morrito. It is associated with feldspar and augite. The augite in a pure granular aggregate forms the outer portion of the vein, while in the center are feldspar and large crystals of hornblende. A fragment in which the cleavage was well developed was examined with a goniometer and the angle found to be the same as that of normal hornblende, namely, 124° 30’. The altered dunite and related rocks east of the Chute are inter- sected by many slender veins contrasting strongly in color. They consist of diallage and a white substance which under the micro- scope is generally completely isotropic. From its close resemblance to the feldspars of the olivine rich rocks which are undergoing a change to a similar cloudy milky substance, it is believed that it belongs among the feldspars. The veins vary in width from half an inch to two inches. In the narrower ones the pale green diallage is confined to the outer edge. The crystals seem to be planted on the walls and to have grown inwards. The center consists wholly of the dull feldspar. In the wider veins the pyroxene is not con- fined to the edge, but is scattered throughout indiscriminately. At the foot of the cliffs south of the Lion’s Head some large pieces of serpentine were found which are cut by white dikes or veins four to five inches wide. The substance of which they are composed is fresh and clear, and contains long, slender, brownish crystals sparingly disseminated along the edges. The walls of the dike are clean cut, with no transition to serpentine. Slides prepared 74 University of California. [Vor. 2. from the center and edges showed an interesting association of min- erals. The white mineral from the center resembles feldspar, but shows no twinning, and is intergrown in a micropegmatitic manner with quartz. The angle of extinction of the supposed feldspar measured on a cleavage crack is very-low. The section prepared from the edge showed only a small amount of quartz intergrown as described, but numerous lath-shaped feldspars twinned according to the albite law. Owing to alteration the extinction angles were diffi- cult to measure, but those obtained indicated that it belonged between albite and labradorite. In portions of the slide the feldspar was observed undergoing alteration to the same cloudy isotropic substance already described. The slender crystals observed in the hand specimen proved to be a pale, slightly pleochroic hornblende. This was shown by the extinction angle of twinned individuals, which is 18°, and by characteristically shaped cross sections with the usual cleavage. The pale color of the hornblende, taken together with its specific gravity, which was found to be 3.065, indi- cates that it is a variety intermediate between tremolite and ordinary hornblende, a hornblende poor in iron. In other sections of similar occurrence many of the individuals appeared perfectly colorless, and are undoubtedly closely allied to tremolite. The specific gravity of the granophyric intergrowth was found to be 2.654. In the case of another dike, a layer of brown hornblende forms the edge, lying between the feldspar and the serpentine, though sometimes separated from the latter by a thin sheet of feldspar. Turner* has described veins in serpentine from Meadow Valley in the Sierra Nevada. The feldspar was proved to be albite by analysis. Similar veins have also been seen by the author in the serpentines in other places in the Coast Ranges. Age.—tThe field relations give no clue to the exact age of these rocks. They are older than the Miocene, but beyond that we can go only by their a.:logy with similar eruptives in this part of the Coast Ranges. Inthe San Rafael Mountains, 40 miles to the south- east, there is a large body of serpentine having associated with it dikes of diabase. The whole has been intruded into rocks of sup- * American Geologist, Vol. XIII, p. 303. F AIRBANKS.] Geology of Point Sal. 75 posed Knoxville age. About the same distance to the north, in the vicinity of San Luis Obispo, are other large bodies of altered peridotite, also intrusive in the Knoxville. As far as is known no eruptives of this kind have been intruded in the Chico. The Point Sal occurrence differs from all others known in the Coast Ranges in regard to the large amount of gabbro accompanying it. Large areas of olivine and norite-gabbros have been found by the author in the Peninsular range in the southern part of the state, but there is no means of correlating them with the similar rocks at Point Sal. It seems more than probable that the rocks under discussion are differentiated portions of the same basic magma which invaded the Coast Ranges through their whole length at some time between the deposition of the upper and lower Cretaceous. Comparison with Other Peridotites of the State-—Peridotites are among the most widely distributed of the eruptive rocks of Califor- nia. They occur through the Coast Ranges froma point a few miles southeast of Point Sal northwest to Oregon. They are met with along the western slope of the Sierra Nevada from Mariposa County north until covered by the lavas. It is a well-known fact that until recently geologists who have worked in California have considered the serpentine of sedimentary origin. M.E. Wadsworth,* who investigated some of the material collected by the old State Geological Survey, is an exception, for all the specimens which came under his observation he believed to be of eruptive origin. In 1891, H. W. Turner + showed that the serpentines of Mt. Diablo are altered eruptives, and expressed the opinion that there is a genetic relation between the peridotite and the gabbro found there. Ina paper published in 1892 the author { advanced the opinion, based on an examination of parts of the Coast Ranges, that the serpentines are all altered eruptives. Later Dr. Palachel| described the serpentine, and associated rocks of the Potrero, San Francisco. There he found a lherzolite generally sheared in an extreme degree, and accompanied by lenses of fine-grained rock * Lithological Studies. + Bull. Geol. Soc. of Am., Vol. II, p. 389. ft Am. Geol., Vol. IX, p. 153. Eleventh Report of State Min. of Calif. || Bull. Dept. Geol. Univ. Cal., Vol. I, pp. 161-179. 76 University of California. [Vot. 2. which proved to be hypersthene diabase and epidiorite. These lenses were believed to be portions of a dike intrusive in the serpen- tine and broken up by a subsequent movement. F. L. Ransome* has described the serpentine of Angel Island, and shown that it originally consisted mostly of diallage. Inclusions occur here also, but their nature and position are such that the conclusion was reached that they could not be intrusions but fragments of an ad- joining rock enveloped in the magma. Observation has shown it to be a fact that nearly all the numer- ous bodies of serpentine have associated with them smaller masses of feldspathic rock which vary in character from gabbro to diabase. The relation of these feldspathic rocks to the peridotitic has been very difficult to determine with certainty. This is due partly to poor exposures, and partly, perhaps chiefly, to the frequently dis- turbed condition of the altered peridotites. Many of the largest areas, namely, those at New Idria and Knoxville, have undergone internal stress and shearing on an extensive scale, and as a result have been reduced to shaly or even pulverent masses. Scattered through these crushed areas are nodules of massive serpentine, and lenses of a gabbroitic or diabasic character. These occur in a man- ner similar to that described by Dr. Palache. The author + has noticed and described the same condition of things existing on a large scale near Knoxville, Lake County. Not only do there occur here lenticular inclusions of what are without doubt foreign bodies caught up in the magma, but also lenses of fine granular crystalline rocks whose relations are puzzling. There are places, however, where these lenses are clearly shown to be portions of disrupted dikes, and it is probable that such is the character of the larger part of similar occurrences. The dikes of diabase on the southern side of the Lion’s Head are very irregular, swelling out and then almost pinching. Should movement take place along the sides of such a dike, it would be broken up, and the fragments separated from each other would present an appearance closely resembling foreign inclusions. . Incip- ient stages of this kind appear in the cliffs. In one case a compar- * Bull. Dept. Geol. Univ. Cal., Vol. I, p. 219. + Eleventh Report of the State Min. of Cal., pp. 69-71. FAIRBANKS. ] Geology of Point Sal. 77 atively narrow mass of serpentine between two gabbro dikes, offer- ing the least resistance to crushing, has been reduced to clay, and contains nodules of a dike not seen in place in that vicinity. Relation between the Magnesian and the Feldspathic Rocks.— The study of the rocks at Point Sal, taken together with what is known of similar areas in other parts of the state, leads irresist- ibly to the conclusion that there isa genetic relation between the feldspathic and non-feldspathic types. It appears also that there is a common sequence for at least some varieties of the rocks thus associated together. The Point Sal occurrence differs chiefly from others in the state in the great variety of rocks, as well as in the presence of a comparatively large area of gabbro. ‘The association of gabbro and peridotite is a very common one in other parts of the world. G. H. Williams* says: “Olivine rocks and serpentines are more or less extensively associated with most of the large gabbro areas which have hitherto been carefully studied and described (e. g., Hartz Mountains, Saxony, Lower Austria, Scandinavia, etc.); and the Baltimore region proves to be no excep- tion to this rule.” In the first of his papers on the rocks of the Cortland Series,} he says, after giving the classification of Professor Dana, diorite, norite, diabase, gabbro, and peridotite: ‘‘This classi- fication may perhaps be advantageously followed, provided it be remembered that no sharp line can be drawn between the different groups, but on the contrary every possible transition from each group into every other occurs.” Bailey{ has described basic peri- dotitic separations from the gabbros of the Lake Superior region, but they are local and belong to the same period of eruption. Judd§ says of the gabbros and peridotites of Scotland: “Locally both gabbros and dolerites are found passing into peridotites by the gradual disappearance of the feldspar and the increase in the quan- tity of olivine.” He says also that segregation nodules of gabbro are found in the peridotites, and wice versa, and also that ‘the so-called ‘segregation veins’ of peridotite are seen traversing the *U. S. Geol. Survey Bull. 28. +American Jour. of Science, Vol. 31, p. 27. {Journal of Geology, Vol. II, p. 817. @Quart. Jour. of the Geol. Soc., Vol. XLI, pp. 358, 359. 78 University of California. {Vot. 2. gabbro, and similar veins of gabbro are found intersecting the peri- dotite masses. The relations of the gabbros and peridotites in the Western Isles of Scotland seem to indicate that, in the heart of these old volcanoes, the feldspar, olivine, and augite tended to segregate in certain cases into masses of various dimensions, and that these masses were, after consolidation, fissured again and again, the fis- sures being injected by different portions of the magma, which were still in a more or less plastic condition.” Bonney,* in describing an area of troctolite and serpentine in Aberdeenshire, says that the feldspathic rock is the later. He quotes Judd as observing a sequence of serpentine, troctolite, and gabbro. In notes on some Ligurian and Tuscan serpentines het describes the occurrence of serpentine and gabbro together in a number of places and expresses the opinion that it can hardly be a coincidence. Bonneyf{ also notes, in describing the serpentines of Ayrshire, dikes of diallage rock cutting serpentine, and gabbro cutting both in turn. From these references it will be seen that the association of feldspathic and magnesian rocks with intermediate types is a com- mon one. There must certainly be a genetic relation, as suggested by several writers. There can be no question that at Point Sal all the extreme variations and successive intrusions had one common parent magma. The Banded Structure-—The remarkable banded and gneissic structures shown in many portions of these rocks are among their most interesting and peculiar features. Although the banding is of course absent from the large area of altered dunite and from a portion of the gabbro at the western end, yet it is such a common phenomenon in almost all facies of the mass, that it deserves a care- ful description. Two fairly distinct divisions may be made, (1) that in which the banding or gneissic structure is due to the more or less perfect segregation of the different components in bands in a fairly homogeneous rock, and (2) that which is due to the string- ing out in long dike-like strips of one or more minerals foreign to the body of the rock, as that of the feldspar and pyroxene bands *Geological Magazine, Vol. XXII, p. 441. tlbid., Vol. XVI, p. 370. {Quart. Jour. of the Geol. Soc., 1878, p. 778. SS eS ee FAIRBANKS. | Geology of Point Sal. 79 in the peridotite. The two are not always distinct, but the division will aid in understanding the phenomenon. The first is conceived to be due to movement during or just preceding the crystallization in a homogeneous magma; the second, to the slight mixing during movement of a heterogeneous magma. A description of the former will be taken up first. In some portions of the gabbro which are perfectly massive there is noticeable a slight tendency to the segregation of the differ- ent components. In this part of the rock, as well as in that which is homogeneous and massive, there could not have been much movement during solidification. Suppose, however, that in such a magma, in which there is a tendency to local segregation, a differential movement should take place, there would result a draw- ing out of the segregated parts of some or all of the constituents to form a gneissic structure. This is best illustrated in the case of the troctolite where the olivine is drawn out in irregular elongated patches which, when they are discontinuous, simulate very closely the structure of a gneiss, without, however, any tendency to schis- tosity. Wherever these shreds become continuous, the different characters may sometimes be observed in the same hand specimen, and there is presented a rude banding. From the latter to the most perfect banding there are all degrees of transition. The feldspars between the shreds or bands of olivine show no common orientation or other signs of having undergone movement during crystalliza- tion, and it must be held that the banding was assumed before the crystallization of the feldspar at least. The olivine may have crystal- lized before or during the movement, probably the latter, and to this fact be due its occurrence in aggregates of many small grains. In the case of the troctolite there is no possible support for the view that the gneissic structure is due to the mixing of heteroge- neous magmas. Given certain conditions of the magma favorable to the segregation of the different components, perhaps in this case of the olivine alone, and a movement of the mass on itself, and the structure described could conceivably be produced. This structure is in no way due to the linear arrangement of the individuals of either of the components, for they have a typical granular form, but rather to the lineation of aggregates. From the almost massive 80 University of California. [Vor. 2 troctolite in which the olivine grains are segregated in irregular. patches, there can be traced a gradual transition to elongated aggregates rudely parallel, and to the appearance of more or less continuous bands of the two constituents. In the case of this rock, which is found in a number of places, the phenomenon is the sim- plest and most easily explainable. In the transitions to the normal olivine gabbro the same structure is to be seen in its various stages of perfection. The gneissic structure is more particularly connected with the presence of the stringy olivine aggregates. The most per- fect banding occurs generally in rocks in which olivine is not an important constituent. This banding is first noticeable in the mas- sive gabbros in the partial segregation of the feldspars and the ferro-magnesian silicates in layers, so that on a clean surface there are indistinct bandings reproduced. It is sometimes noticeable only on the weathered surfaces through the removal of the dark constit- uents. In portions of the gabbro where this structure is most common it is far from being uniform, and there are quite abrupt transitions from the obscurely banded or gneissic rock to one in which the banding is comparatively regular. Asa general thing the bands are not continuous for any great distance, but thin out and are replaced by others. There is an exception, however, in the case of the gabbros near Point Morrito, where the bands are exceedingly regular for many feet. The variation in thickness is. particularly noticeable in the case of the feldspar, while the olivine is always found in very thin bands. In some facies of the rock the banding appears only in the microscopic examination. A dark but apparently massive hypersthene troctolite showed, in thin section, the hypersthene and feldspar together in a narrow band to the total exclusion of the olivine, and another band of feldspar almost free from hypersthene. In this specimen the olivine aggregates show no noticeable lineation. ; A specimen obtained at the foot of the cliffs near the Head is quite remarkable. The rock contains in order of their importance augite, brown hornblende, olivine, feldspar, hypersthene. A hand specimen three inches wide showed the following bands: First, one in which hornblende is the most important dark mineral, then a band of augite one-half inch wide, having on each side a very nar- FAIRBANKS. | Geology of Point Sat. 81 row band of feldspar, then hornblende with some feldspar, followed by narrow bands of feldspar not strongly marked. The augite occurs in a band free from the other constituents, having a predom- inating number of the crystals with their vertical axes approxi- mately normal to the walls. Banding is also exhibited in an interesting manner by many of the narrow basic dikes which are among the latest of the intrusions. It is due mainly to the unequal distribution of the feldspar. It is hard to understand how the banding in this case can be due to aught else than movement in an originally homogeneous magma, in con- junction with a tendency to segregation and slight differences in time of consolidation of the different components. The dike of serpentine in the gabbro west of Point Morrito which contains the abundant inclusions of gabbro has already been mentioned. The inclusions range in size from three inches in great- est diameter down to mere specks, and are so arranged as to give the appearance of banding. It would seem that here is a clue to one of the causes of the phenomenon under consideration. The inclusions would play the part, during movement, of constituents already solidified. - The body of the dike which consists wholly of diallage and decomposed olivine is distinctly banded in several places by lighter colored feldspathic layers. These are quite sharply bounded and it is quite possible that they are due to the mixing of two heterogeneous magmas. The large body of feldspathic wherlite or picrite inclosed in the gabbro presents a linear arrangement of the feldspathic aggregates which are dotted thickly through it. These aggregates are not massive but consist of feldspar and serpentine in about equal pro- portions. They are frequently drawn out in lenticular patches two or three inches long. Segregation must have been contempora- neous with movement. In the peridotite at. Point Morrito there are areas in which the diallage and olivine have been segregated in large bunches, but unaccompanied with movement. In other spots there are irregular patches of picrite in a matrix consisting chiefly of olivine. In both of these cases a differential movement at the time of consolidation would have produced banding. The feldspathic streaks occurring in the dunite and other varie- 82 University of California. [Vor. 2. ties of the peridotite are probably due to the mixing of two partially differentiated magmas. They have not been subsequently intruded, for no sharp line of contact is visible, and the darker portions shade off into the serpentine. This is illustrated along the base of the cliffs at Point Morrito. Below the olivine-pyroxene rocks there are parallel banded layers, which, although differing from each other considerably and appearing on first examination to be dikes, yet show more or less blending across the strike. Banding of the kind observed at Point Sal is a common charac- teristic of the deep-seated basic rocks in many parts of the world. Prof. A. C. Lawson* says of the anorthosites of Beaver Bay, north shore of Lake Superior: ‘‘The original allotriomorphic granular structure has not been disturbed, and it is highly improbable that the banding is in any way associated with shearing action after the final consolidation of the rock. It seems to the writer to be essen- tially due to some local chemical differentiation associated with movement in the thickly viscous magma prior to crystallization.” Bailey} mentions a banding in the gabbro of the Lake Superior region. He describes it as being confined to the peripheries of the great gabbro area. ‘“ The thickness of the bands ranges from 20 or more feet down to the fraction of an inch only.” Banding of the type under discussion is very prominent in many portions of the British Islands, and the English geologists have given a great deal of study tothe question. Bonney and McMahont describing the crystalline rocks of the Lizard District note a band- ing or foliation in the serpentine. They say: “In the opinion of the authors the structure can only be explained as a fluxion-structure, that is to say, as being the result of traction acting on either an imperfectly blended mixture of two magmas, differing slightly from each other in composition, specific gravity, or fluidity, as in the case of the banded felsite or rhyolite, or on a mass in which com- plete crystallization has been arrested by subsequent motion, at a time when only a portion of the constituent minerals had separated *Bull. No. 8, Minn. Geol. Survey, p. 15. {Journal of Geology, Vol. II, p. 817. tQuart. Jour. of the Geol. Soc., Vol. XLVI, p. 474. FAIRBANKS. | Geology of Point Sal. 83 themselves out from the magma.” They state that no signs of crushing are apparent in the rock. Bonney* noted a similar appearance in the lherzolite of the Lac de Lherz, which he attributed to a “ fluidal structure.” McMahon} advanced the following opinion to account for the foliation of the Lizard gabbros: “That the latter was produced by ‘shearing motion’ on the rock after its consolidation had advanced considerably, but was still incomplete.” He notes also a rapid passage in some of the dikes from a foliated to granitic structure, and attributes the latter to greater solidification. Harker{ describes a mottled appearance in some hornblende picrites due to the “mingling of dark and light patches or the sep- aration of white spots ona black ground,” and also a banding, as follows: “This last-mentioned appearance seems to be caused by the difference between bands alternately rich and poor in olivine, a character noted by Reusch in the saussurite gabbros of the Bergen district. There are even distinct bands less than an inch in width, which under the microscope appear as veins entirely composed of serpentinized olivine with much secondary magnetite.” Teall§ in an article on the metamorphosis of the Lizard gabbros considers the foliation the result of pressure or regional metamor- phism, saying: “Is it an original or secondary structure? That it is due to a differential movement in the mass after the separation of the original constituents will I think be admitted on all sides. The only question that can arise is whether the movement was in any way connected with the intrusion of the rock.” Geikie and Teall|| have given in detail the structure of some Tertiary gabbros in the Isle of Sky. They recognize four distinct varieties: ‘(1) dark, fine-grained granulitic gabbros, resembling externally basalt rocks; (2) well-banded gabbros composed of irreg- ularly alternating bands and laminz of the several constituent min- erals; (3) coarse massive gabbros destitute of any banding; and (4) *Geological Magazine, Vol. XVI, p. 370. { Lbid., Vol. XXIV, p. 76. tQuart. Jour. of the Geol. Soc., Vol. XLIV, p. 457. @Geological Magazine, 1886, p. 489. ||Quart. Jour. of the Geol. Soc., 1894. 84 University of California. [Vou. 2. pale feldspathic veins.” Their description of the banded portion is as follows: “Each of these banded sheets consists of many parallel layers of lighter and darker material. The component layers vary in thickness from mere pasteboard-like laminz to beds a yard or more in thickness. Ona single exposed face of rock they may be seen to be as parallel, regular, and continuous as sedimentary depos- its. An intimate union exists between the material of the succes- sive bands. They are welded into each other by the mutual pene- tration of their component minerals.” In the locality described the authors have not noticed any lineation of the individual crystals, although in some of the gabbros of the Inner Hebrides there is present a flow structure with drawn-out feldspars. ‘‘The more basic portions are not confined to the margin of the masses, but alternate with the more feldspathic portions to form the banded complex.” They believe that the anorthosite rocks of Canada originated under much the same conditions. In conclusion the statement is made that “the banding is the result of the intrusion as sills of a heterogeneous magma, the heterogeneity produced by causes operating elsewhere and probably at lower levels in the earth’s crust. Then came the intrusion of the heterogeneous magma as sills, and it was by the deformation of the molten mass during intrusion that the banded structure was produced.” It is the opinion of the author that the banding at Point Sal is in large part due to other causes than that of a differentiated magma which subsequently underwent differential movement; that this was concerned, but that it alone could not have produced the phe- nomena. The most perfect banding at Point Sal resembles closely that in other regions which have been referred to, and generally considered to represent the mingling of heterogeneous magmas during move- ment, but the fact that here there is plainly to be discerned transi- tions from the regular and even banding to that of discontinuous bands, then to the gneissic structure, and finally to the massive condition, leads irresistibly to the conclusion that here at least the different portions of the rocks in which banding is pronounced solidified from what was a fairly homogeneous magma previous to movement. There was, however, a tendency to the segregation on | ; i a : FAIRBANKS. ] Geology of Point Sal. 85 asmall scale in certain portions of the magma as the temperature lowered prior to consolidation, and in conjunction with this a move- ment of the magma on itself took place in the conduit. These two things, taken together with the fact that there were slight differences in the time of crystallization of the different constituents, would tend to produce linear aggregations of more. or less purity. It seems that the greater part of the segregation took place during the movement, but that this was not a segregation of partially con- solidated material, except perhaps the olivine, for the crystals of the different bands present no more appearance of movement during their period of formation than do those of the massive varieties. The layers interlock as Geikie and Teall have described. It is quite probable that the olivine, which always occurs as aggregates of numerous small grains, crystallized during the movement, but in the case of the feldspars movement must have ceased when they began to form. None of the other dark silicates show such peculiar stringy masses as the olivine. Discussion of Magmatic Variation.—It is not the plan here to enter into any detailed discussion of the question of differentiation in rock magmas. The work done in this line has been thoroughly discussed by Iddings, Brégger, Rosenbusch, and others. The se- quence, however, of the intrusions at Point Sal will be discussed, as well as their relation to similar rocks in California and other parts of the world. Iddings * states the general law of differentiation to be as fol- lows: “The variation in the composition of igneous rocks, which constitute a series of eruptions at any volcanic center, is the result of the chemical differentiation of some intermediate magma.” ‘The general succession is from a rock of average composition through less silicious and more silicious ones to rocks extremely low in sil- ica and others extremely high in silica, that is, the series commences with a mean and ends with the extremes.” Geikie | has formulated the general succession of eruptive rocks in Great Britain as follows : “ With the important exception of the Snowdonian region, and possibly others, we find that the earlier * Bull. Phil. Soc. Wash., 1892., pp. 151, 145. + Quart. Jour. of the Geol. Soc., Vol. XLVII. 86 University of California. [VoL. 2.. eruptions of each period were generally the most basic, and that the later intrusions were the most acid.” Teall * says: “Given one reservoir and continuous cooling there would be one sequence, the basic rocks should precede the acid. This has been the case in many regions, but the rule is by no means without exceptions. The exceptions may be due to the ex- istence of two or more reservoirs or to the accession of heat or of fresh material during the process of consolidation.” In a paper by Geikie and Teall + there are some interesting ob- servations on the differentiation of magmas: “We often find what is a connected series of intrusions exhibiting a wide range in chem- ical and mineralogical composition, and certain definite though probably not very great differences in age. Such a plutonic area taken as a whole, though forming a petrological complex, is a geo- logical unit. The complexity in such cases can not wholly be accounted for by differentiation zz s¢tv. The more abrupt changes require the hypothesis of successive intrusions, which probably rep- resent differentiation elsewhere of the same general character as that which has taken place to a smaller extent zz sztu. We recognize, therefore, two kinds of petrological complexity in plutonic areas, (1) differentiation zw sztu, (2) successive intrusion.” In the study of the Yogo Peak igneous rocks, Pirsson{ found a progressive differentiation from one end to the other ofa large intrusive mass, to which he applied the term “ facies suit,” after Brogger, who used it to designate the differentiation of a mass in its final resting place. Mr. Pirsson also found in the rocks of Square Butte, in Montana, a progressive increase in the ferro-magnesian silicates toward the outer border. Brogger § reaches the conclusion that there is a fairly common sequence. ‘The series basic, Jess basic, acid appears so often among the deep-seated rocks that we must look upon this series as a normal one; the sudden return to the basic is known in many occurrences, but appears to fail often. . . . The deep-seated * Nat. Sci., Vol. I, No. 4. + Quart. Jour. of the Geol. Soc. 1894. tAm. Jour. of Sci., Vol L, p. 467. 4 Die Eruptionsfolge der Triadischen Eruptivegesteine in Sudtyrol. FAIRBANKS.] Geology of Point Sat. 87 rocks of one period of eruption are the differentiation products of a common magma basin. The differentiation is brought about by a diffusion according to the order of crystallization toward the outer surface. The more remote the periods of eruption, the more differ- entiated should be the products erupted. . . . The series of surface rocks is not necessarily the same as that of the deep-seated rocks. These are in large part controlled by secondary differentia- tion, being a repetition of basic, acid, basic, etc.” He says that most authors have not made this distinction. In conclusion he adds : “ In general, the farther the magma basin is removed from the magma trunk, the greater the amount of differentiation which has taken place, so much less regularity will there appear in the series of eruptions. Any irregularity or departure from the rule in the deep-seated rocks must be all the more pronounced in the surface rocks.” Brogger also emphasizes the point that his sequence is that for regions removed from mountain-making influences. In many respects the views of the investigators quoted do not differ greatly. It would seem, however, that in the majority of instances there are complicating causes at work which so affect the series of eruptions that no statement can be formulated which will hold true in all. Iddings’ view of continually greater extremes in the character of eruptions of any one period from a common reser- voir is only one aspect of the truth, of which that of Teall and Brogger, of a continually increasing acidity, is another. In moun- tain regions, where disturbances are taking place, the sequence must of necessity be different in many cases from that which would occur theoretically in a magma and its apophyses when not so affected. At Point Sal there can be observed both kinds of petrological complexity described by Geikie and Teall, differentiation zz sztw and successive intrusion. The gabbro and peridotite were each fully differentiated in some deeper-seated region, while in each secondary differentiation took place during the movement upward or after attaining its present position. Judging from the surface exposures the gabbro can not form more than one-fourth of the total mass, and it may be less, so that the common magma must still have been very rich in magnesia. Owing to the fact that not all the different 7 838 University of California. [Vor. 2. kinds of dikes appear in any one spot, their succession can not always be determined. The main body of the gabbro, and perhaps some of the diabase along the northern side of the complex, are undoubt- edly the oldest of the intrusions. The peridotite at Point Morrito has been intruded through the gabbro and is apparently continuous with the large body of altered dunite toward the east. At Point Morrito there are dikes of greatly varied character later than both the gabbro and peridotite. As a general thing these dikes are poorer in feldspar than the normal gabbro. They are very fine grained, but granular in structure. The dikes of diabasic character occur in many parts of the complex, in both the gabbro and peri- dotite. The succession, as far as determined, is as follows: gabbro and some diabase, peridotite, dikes of granular structure and intermedi- ate composition, diabase and ophitic quartz-diorite, and feldspathic veins. A partial analysis was made of the feldspar in the banded troctolite, with the following result: SiO, 42.6, Al,O,; 383) CaO 18.65. An estimation of the silica in the partially altered dunite resulted in 41.3 per cent. This would give an extreme range in silica between the peridotite and the ophitic quartz-diorite of 24.7 per cent. If the pegmatitic quartz-feldspar veins were taken into account, the range would be still greater, for in them the silica reaches 73 percent. The succession in general is basic, more basic, and acid. The occurrences of the acid rocks are, however, compar- atively insignificant in volume. The larger number of the various eruptive bodies do not differ much as far as the silica content is con- cerned. It is, however, when we look away from the silica ratio to that of the alumina, magnesium, and calcium, that the extreme dif- ferences in mineralogical composition are understood. In addition to the very common associatian of diabase and peri- dotite in many parts of the state, there are localities where gabbro is also found with peridotite. Whether this gabbro is of later origin, or fragments of an earlier consolidation, or secretions from the magma, observation as yet seems not to have definitely settled. It is a well- established fact of common occurrence to find inclusions of foreign bodies in the peridotite. This is particularly prominent at Knox- ville, Lake County, and on Angel Island. Although Point Sal is a an FAIRBANKS.] Geology of Point Sal. 89 the only spot yet known where the feldspathic separation preceded the peridotitic, yet it is certain that the latter is almost invariably followed by dikes of diabasic character. The magma basin, from which these numerous bodies of perido- tite were derived, could have been no local one. They occur through nearly the whole length of California west of the Sierra Nevada, and extend for an unknown distance northward. As far as the author’s observations have been carried, there appears to have been only one period of intrusion in the Coast Ranges. The eruptions cut strata of Knoxville age and are overlain by the Chico. The diabase sometimes Occurs on one side of the peridotite and some- times within it, but at Point Sal, if there can be any distinction made, it is that the magnesian rocks are confined more to the center of the mass, and the feldspathic to the borders. The various masses reached their present position already fully differentiated. Second- ary differentiation took place in both the feldspathic and magnesian facies, but whether the distinct bodies of gabbro, diabase, and peri- dotite are segregations in the common magma basin of the ‘‘petro- graphic province” or in the conduit through which the local pro- trusion took place, is difficult to say, although it would seem that the probabilities are in favor of the latter view. If the view that the crust of the globe becomes progressively more dense and basic with increased depth is a correct one, then the peridotites when they are not merely facies of more acid rocks must be conceived as originating at great depths. This basic material forced up through fissures over a wide area on the Pacific Coast, occurring everywhere as independent masses, and not mere basic secretions from an acid magma, indicates that it originated in a deeper basic portion of the crust. Under the conditions of great pressure and high temperature existing at great depths, diffusion would be impossible and the composition would remain homoge- neous. The absence of any large bodies of acid rock which appear genetically related to the peridotites strongly supports the view of the existence of a widely distributed basic magma of nearly homo- geneous composition. The differentiation which has taken place in this basic magma in the chimneys has been a very complete one as a general rule. The gabbro is fully as feldspathic near the perido- go University of California. [VoL 2. tite as at any other point, while the feldspar in the latter is appar- ently due more to resorption than to a lack of differentiation. The extreme variations in the gabbro are due to secondary differentia- tion, while the dikes of intermediate character in the peridotite rep- resent either a differentiation of the latter or a partial resorption of the feldspathic facies at a greater depth. Where differentiation has taken place on a small scale, as at Point Morrito, resulting in stringy masses and nodules of the different constituents only a few feet in diameter, it would seem that the phenomenon could not be due to differences of temperature and pressure, but, under favor- able circumstances of great liquidity and slow cooling, to a tendency to segregation of similar molecules through chemical affinity. The theory which Rosenbusch* has advanced to account for the differentiation of homogeneous magmas seems to be applicable more than any other to the phenomena observed here. He con- ceives that the original magma within the earth was homogeneous, and that it separated into partial magmas of different composition according to the laws of chemical affinity. The two extremes of this process he terms the /oyaite (NaK)AISi,, and the jperidotite (MgFe)Si magmas, with an intermediate one (CaAl,Si,). As the last increases in amount, the “metal kern,” representing the ferz- dotite magma, becomes more easily soluble in that of the foyatte magma. There is certainly shown here a tendency to the separation of certain molecules independent of differences in temperature. One of these is rich in magnesia and iron, the other in calcium and alumina. Geological Laboratory, University of California, May 1, 1896. *Min. u. petr. Mitth., Vol. XI, pp. 144-178. FAIRBANKS. ] Geology of Point Sal. gl EXPLANATION OF PLATE 2. The letters in the illustration refer to the following minerals: F, feldspar; P, pyroxene; A, analcite and its alteration products; M, magnetite; G, glass. FiGurRE 1.—Volcanic ash in the lower Miocene, showing the pumiceous glass occasionally inclosing feldspars. x 20. FiGurE 2.—Augite-teschenite in which the feldspars are partially replaced by a pegmatitic intergrowth with secondary feldspar. x 20. FIGURE 3.—Panidiomorphic facies of the augite-teschenite. The analcite occurs in large areas bounded by the idiomorphic faces of the other components. The magnetite is later than both augite and feldspar. x 20. FiGuRE 4.—Large augite plate with poikilitic structure. There are shown seven small polyhedral areas of altered analcite, partly in con- tact with the augite and partly inclosed in the feldspars. ~ 21. FIGURE 5.—A large plate of augite containing feldspar crystals of various sizes and often showing jagged terminations. Disconnected areas of altered analcite appear in the center of the augite crystal and are bounded in part by crystallographic planes of the latter. x 20. FiGuRE 6.—Another of the poikilitic augite crystals from the teschenite. Is contains small lath-shaped feldspars, while on one edge there is a large area of analcite which penetrates the augite and it bounded by crystal planes of the latter. x 20. VOR D2, Plnaai : UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology Vol. 2, No. 2, pp. 93-100, PI. 3. ANDREW C. LAWSON, Editor ON SOME PLIOCENE OSTRACODA From Near Berkeley | ‘BY . FREDERICK CHAPMAN onvoneeetaneang,. d eo sees, a —7 < R Yi Za VE Ny Wy ely: fo N: | % 4 es // ais \\' —Ss | Sx XY, Y, eoncesPQecenany, | x oe s, BERKELEY ‘PUBLISHED BY THE UNIVERSITY AUGUST, 1899. PRICE, 25 CENTS ( ME, UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology Vol. 2, No. 5, pp. 119-153 PI. 4 ANDREW C. LAWSON, Editor THE meOROGY OF VOlNi KEYES: PENINSULA BY F. M. ANDERSON CONTENTS. Page. Introduction— CaneralgS tatem ent crccneccscunteechiamicaesvladsceseteroeasassecesiedecdterersinesctsitevsciees 120 BOUT AI CSttecitanscasteaversctnestececensr in ocne tie cutareconatedsstechitcesteaia sews eevee s beces 121 NPIFOLAUITO eceretne tones eneae rslcuecewacestcanccsenens ss ~eCuC op do Paco onic Boab edhGecaedede 121 Gai Cemeenetnsosdncaere sea acn cemrtienaas rvs cscs scare sasesessatel cescederssdscenaetset ts \ CX s \, 38°00" , | Crystalline Franciscan Series || Granite Miocene Shale | with Sandstone} Limestone Recent Sands Pleistocene Sandstone \ TAN RA es ro) SW Abbott's Lagoon oO. >> \ 2 im eS : VQ A SY Ke | Interval, 200’ UY, AN Say : A : Wi See Se i AN We Zz 3 SCALE OF MILES GEOLOGICAL MAP POINT REYES PENINSULA by F. M. ANDERSON BERKELEY, CALIFORNIA ‘“iPoint Reyes] 2 \ ANDERSON. ] Point Reyes Peninsula. r23 underlain by Miocene sediments. No more granite is seen along the shore from this point southward, but along the bay they are only imperfectly covered. Along this side of the peninsula the granite comes to the surface and is more or less continuous with the second area of granite further south. This second area, which forms the largest body of granite on the peninsula, lies west of the head of Tomales Bay. It embraces Vision Hill, and a, large portion of Whittenberg Hill, with almost the whole of the ridge connecting them. From near the entrance of Bear Valley, the eastern margin of the granite follows the county road toward, and along the shore of the bay to the point, at which the road turns westward through the hills. Here it is interrupted, for a few hundred yards only, by an exposure of thin- bedded siliceous schist, which rests upon the granite at the water’s edge. Northward, beyond this point, the granite is exposed along the shore for several miles. Along the western flanks of the ridge which follows the shore of the bay the Miocene sediments overlie the granite, and make its western boundary much less regular. Thearea widens gradually, however, from the north, where it is less than a mile in width, until at a point opposite the head of Tomales Bay, its greatest width is a little more than three miles. Scattered patches of sedimentary rocks cover the northern portion of this area. A tongue of these sediments occupies the depression to the north of Vision Hill, while the bold spurs of the hill farther to the south extend the granite westward into the border of the Miocene rocks. The most southern exposure of granite belonging to this area that was observed, was on the eastern brow of Whittenberg Hill, opposite the hamlet Olema. The third area of granite is distinct and entirely separated from the preceding two, at least superficially, by the sedimentary rocks of the Miocene in the lowlands surrounding Drake’s Estero. This area of granite is at the extreme southwestern promontory of the peninsula. It is smaller than either of the other two areas, and forms only a narrow ridge extending in an east and west direction for about a mile and one-half. It has a general elevation of about five or six hundred feet, though at its eastern end it drops some- what lower than this. The southern face of this ridge is a precip- 124 University of California. [Vot. 2. itous ocean cliff for its whole length. The Point Reyes Light stands at its western terminus. At the beach, below the govern- ment dwellings, is the most western exposure of the granite. It is here overlain by massive beds of conglomerate, but it rises from beneath these to the summit a little farther to the east, and then forms the remaining three-fourths of the sea-cliff extending east- ward. This narrow strip of granite does not exceed a width of a few hundred feet, except at its eastern end, where it juts into Drake’s Bay. This projecting headland is of granite, and from this a narrow strip of granite follows the shore of Drake’s Bay north- ward for half a mile. It is then replaced by beds of very coarse conglomerate and sandstone. Petrograplic Character.—In the field the granites of Point Reyes appear as moderately coarse-grained, light gray rocks showing rough and rounded surfaces where they are firm, though usually they are much decomposed. Where erosion is not rapid the rocks are decayed, often to a depth of a dozen feet or more, but on the summits where harder phases protrude, and in the deep ravines where the erosion is greatest, and along the shore the rocks are firmer and often more angular. All of them, where favorably exposed, are seen to be greatly shattered and broken, and testify to the large amount of disturbances they have undergone. The rock is mostly unfit for quarrying purposes on this account, since it is not easy to find many blocks of any considerable size. Veins of aplite occur, and are not uncommon, along the eastern side of the peninsula and at its northern extremity. Pegmatitic rock is sometimes found which, occasionally, is very coarse-grained. These granites are to be classified as normal biotite granites. Quartz is in only moderate proportions, and both orthoclase and plagioclase feldspars are present. As to the quantity of biotite present, there is considerable variation. Basic segregations are common, in which there is no quartz and little feldspar, while on the other hand there are phases containing but little biotite. Horn- blende is not abundant, or, rather, it is almost entirely absent. There are three prevailing types of granite, one of which is confined to the southwestern area, and one almost wholly to the northern. ANDERSON. ] Point Reyes Peninsula. 125 One common type is a moderately coarse-grained rock in which biotite is so conspicuous as to give it a decidedly dark color. Orthoclase is abundant, though not the prevailing feldspar. Pla- gioclase, approaching oligoclase, predominates, twinned commonly on the albite law, while the pericline law is not infrequent. The plagioclase has the most marked idiomorphic tendency of the constituent minerals. Quartz appears in the sections as rather large allotriomorphic plates, very irregular in shape. Another type is similar to this in its composition, but the quantity of biotite is reduced to a very subordinate amount. This rock is more compact, finer grained, and lighter in color than the other, and better resists weathering. This is more common at the northern angle of the peninsula. ‘“ Mussel Rock,” on the beach west of the Pierce Ranch, is of this variety. It stands out in the ocean, almost entirely severed from the mainland of the Point. The rocks in this vicinity show a tendency to segregation into basic and acid zones. Veins of aplite are frequent here, cutting the rocks in various directions. Still, the most common type of granite on Tomales Point is the coarser one, in which biotite forms a con- spicuous proportion. The most common accessory mineral here is titanite. It occurs in large idiomorphic crystals, some of which are one-fourth of an inch in length, or even larger. Magnetite is common along with chlorite, both of which seem to have resulted from the alteration of brown biotite. This alteration has resulted in the wedging apart of the cleavage plates of the biotite, producing an interlocked structure of the biotite and the chlorite. The chlorite is strongly pleochroic in sections, showing the basal cleavage, but in sections parallel to the cleavage it is almost isotropic. Narrow bands and scattered scales of chlorite are common in some of the sections. The feldspar contains many inclusions of hornblende and biotite. The granites of the larger area are more varied in their character than those of the northern area. The rocks are not so well exposed, since they have no ocean cliffs, and are more thickly covered by underbrush, which protects them from erosion. Yet in 126 University of California. [Vot. 2. the deeper canons and on some of the high ridges, one is able to find firm rock, though not often fresh rock. At the two higher and southernmost summits of Vision Hill the granite is coarse-grained and dark, with a large amount of biotite, and occasionally large crystals of feldspar and quartz. At the northern and lower summits the texture of the rock is more uniform and of a finer grain. It has here been pressed and broken into a columnar appearance, consisting of large, roughly cubical blocks. At one of the northern summits the rock is peculiar from the large amount of magnetite which it contains, seemingly as an original mineral. It is a fine-grained rock, containing both ortho- clase and plagioclase, with quartz, hornblende, and biotite. The biotite has been altered to chlorite to a limited extent. The mass may be only a large secretion from the granite, in which there is an unusually large proportion of iron oxide. At the head of Tomales Bay the rock exposed in the road-cuts is a dark gray granite, with zones of basic rock, and with veins of quartz and aplite. One slide of this rock shows a large crystal of titanite, though it does not seem to be common here. All the rock con- tains iron oxide and shows the alteration of biotite to chlorite. At the western base of the ridge occupying this area the rock is compact and resists weathering more perfectly. In other respects it is similar to that just described. The pericline law in the twinning of the feldspars is frequently noticeable. A third type of granite is that of the southwestern angle of the field. It is essentially similar in composition though physically different from that of the other areas. This granite is of the porphyritic type, similar to that described by Professor Lawson’ from near Monterey. It is of uniform character throughott, the rather fine-grained ground-mass consisting of a compact aggregate of quartz, orthoclase, and plagioclase with no large amount of biotite. In fresh surfaces it has a characteristic vitreous appear- ance. The phenocrysts are large crystals of pink orthoclase, varying in size from one-fourth of an inch to two inches in length. They are mostly twinned on the carlsbad law, though 1Bull. Dept. Geol. Univ. Cal., Vol. 1, pp. 9-15. han POMMREANY SARIRANt eC my ANDERSON, ] Point Reves Peninsula. 127 this is not always to be seen. As far as was observed no parallel orientation could be noticed in these crystals, as is sometimes the case in the Monterey granites. Orthoclase is much more abundant in these rocks, as well as quartz, though plagioclase is the domi- nant feldspar. As a rule, the rocks of this area are less broken and more resisting to the weather than those of the other areas. Aplites and basic segregations are not common. Veins of calcite were seen at several points penetrating the rocks. Usually they were of only an inch or more in thickness. There is yet one other occurrence of granitic rock so peculiar in its character that it deserves mention. It belongs to the larger area, and occurs near its southeastern boundary in a cafion west of Olema. It resembles, at first glance, a partially decomposed aplite, and was at first taken to be such. Further study of it showed, however, that its peculiar appearance was due to a complete and very thorough crushing it had undergone. It occupies a zone of niore than half a mile along the canon, with a width of at least one or two hundred yards. It is perhaps a fault breccia. Under the microscope it shows angular fragments of quartz and feldspar cemented together in a matrix of pulverulent and partially kaolinized material containing some calcium carbon- ate. Both orthoclase and plagioclase fragments are plentifully distributed through the mass along with quartz, and all of them are very much cracked and shattered. Few traces of biotite or any dark mineral are to be found in it. It lies in the midst of a system of intersecting faults, and serves to indicate how great the disturbances of this district have been. In most of the granites of the peninsula:the more transparent minerals show an undulous extinction when turned between crossed nicols. This is very noticeable in the rocks of Tomales Head, both in the quartz and in the orthoclase and even in the plagioclase. In the rocks of Vision Hill it is even more conspicuously seen, while at the southwest angle of the field it is apparent only in the quartz and orthoclase. All the larger crystals show a large amount of fracturing, and irregular cracks are very abundant. This still farther shows the great stress to which the rocks have been subjected. 128 University of California. [Vot. 2. Endomorphism of the Granite—The relation of the granite of the peninsula to other formations will be more fully stated in the succeeding paragraphs, yet it may be incidentally referred to here for the fuller discussion of the granite itself’ Lacroix has described the occurrence in the Pyrenees of an acid biotite granite which has been intruded into a series of calcareous and siliceous sedimentary rocks. Among the metamorphic alterations effected in the zone of contact was the development of more basic phases in the granite itself where it was found in contact with limestone. Quite similar relations are to be seen on the peninsula. Imme- diately beneath a zone of crystalline schist developed in the sedi- mentaries is a zone of granite different from any other that was found in the field. A thorough study of this interesting occurrence was not undertaken, although there can be no doubt that it would be well rewarded. The character of the granite at this contact is not uniform. It seems, in fact, to be quite variable. Much of it is a very dark, rather fine-grained, hornblende-bearing rock, containing only a little quartz and not a large amount of feldspar. The hornblende is of the green variety and considerably more abundant than the dark grains of biotite. The feldspars are similar to those of the normal granite in which orthoclase predominates. Oligoclase is common and andesine is occasionally seen. These are the only idiomorphic elements found in the rock. Magnetite occurs in scattered grains resulting apparently from the alteration of hornblende. Another phase of the granite which is perhaps less basic than this is a light- colored garnetiferous variety which contains no hornblende and a smaller amount of biotite than most of the normal granite. In other respects it may rank with the normal variety, except that it contains great numbers of small pinkish-colored garnets resembling some of the lime-iron varieties. This rock was found not far from the preceding variety below the zone of crystalline schist. Other basic phases are common but were not sufficiently studied to make definite statements in regard to them. Relation to Other Massifs—The geological relation of the granites of the Coast Ranges of central California to those of other parts of the state, or of the coast, is a very interesting question. ANDERSON. ] Point Reyes Peninsula. 129 Too little is yet known for any satisfactory comparison, but it is worth while to record a few observations upon this topic which may be in the line of reaching some conclusion. Granites have been more or less perfectly described from several points in western California south of the area of Point Reyes peninsula, as, for example, from Montara Mountain,’ Monterey and Carmelo Bays, and from near San Luis Obispo,’ with the exception of some of the “Montara granite,” which Professor Lawson calls a hornblende- biotite granite. All the types yet described are rather acid rocks in which biotite is the dominant fero-magnesian mineral. Quartz is generally abundant and the feldspars are both orthoclase and plagio- clase. It is a remarkable fact that the porphyritic type with large phenocrysts of orthoclase, twinned on the carlsbad law, characterize three of the four regions thus far studied. This type has been well described from the vicinity of Monterey by Professor Lawson. In many respects this occurrence is paralleled by the porphyritic facies, if it may be so called, that occurs at the southwest angle of the Point Reyes area. Dr. Fairbanks mentions the same char- acter as belonging to some of the granite near San Luis Obispo. The most common accessory mineral, found plentifully in at least three of these localities, is titanite. Other characters more strictly chemical will doubtless be recognized in time which shall prove more satisfactorily the essential identity of these granites, but at present these features are noticeable and have more or less weight. Northward along the coast or from its near vicinity no granites of a similar nature have been described, though there is probably an equivalent and contemporary rock to be found in the Klamath Mountains. A coarse-grained, quartzose, biotite granite makes up a large part of the central core of the Trinity Mountains at the head of the south fork of Salmon River. This granite has been intruded into a series of Paleozoic sedimentary, and older schistose rocks mentioned in another paragraph. The porphyritic character has not been noticed there, but further northward in the Siskiyou Mountains a similar granite occurs at Ashland peak and eastward, 1y5th An. Rept. U. S. Geol. Sur., 1894, pp. 408-415. 2 Bull. Dept. Geol. Univ. Cal., 1893, pp. 9-18. ’Jour. Geol., Sept.—Oct., 1898, p. 567. 130 University of California. [Vol. 2. in which orthoclase is very abundant in large crystals and carlsbad twins that make the rock decidedly porphyritic. Mr. H. W. Turner has described a “granite-porphyry” frem the Sierras’ of Butte County, California, that at first appears to resemble that of the Coast Ranges. It appears, however, for the most part to be confined to dikes, or at least already very limited. The pheno- crysts are said to be of quartz and plagioclase. East of the Yosemite Valley and at other places in the Sierra Nevada’ porphy- ritic granite occurs which bears a much stronger resemblance to that of the Coast Ranges. According to Professor Lawson’ there is some resemblance between some of the granite of the Coast Ranges and the “ granodiorite” of the Sierra Nevada. Writing of the rock from near Monterey he says: ‘The ground-mass of the rock certainly belongs to that intermediate type for which Becker has proposed the term gvaunodiorite.’ Perhaps there is also some resemblance to be found in the hornblende-bearing facies of Montara Mountain. On the whole, however, there appears to be something of contrast in the types most characteristic of the Sierras and of the Coast Ranges. Basic granites of the types common in the Sierras are not much known in the Coast Ranges, while on the other hand the acid biotite granites, such as have been described from the Coast Ranges, are relatively much less abundant in the Sierras. Yet too little is known of either region to make any general comparison either satisfactory or safe. PRE-GRANITIC CRUST. It seems a little remarkable that so few remnants of the ancient crust, into which the granites of the Coast Ranges arose, have been definitely recognized as such. There are traces of its rocks found in the conglomerates of the Tertiary and older periods in many places where such beds occur, but there are few, if any, extensive formations that have been clearly shown to have formed a part 177th An. Rept. U.S. Geol. Sur. )pp..472, ete: 2r4th An. Rept. U. S. Geol. Sur., pp. 478-480. * Bull. Dept. Geol. Univ. Cal., Vol. 1, p. 15. ANDERSON. ] Point Reyes Peninsula. 131 of this pre-granitic crust. At least two members of this ancient series have probably been recognized in this field. Marble—Immediately west of Point Reyes Station, upon the crest of the ridge, is a body of white, crystalline limestone which has at some time been used to a limited extent for making lime. It is almost pure white and highly crystalline. It contains numerous scales of graphite disseminated through it in clusters and patches. The best exposure of it is on the “old road” which crosses the summit from the ,.head of Tomales Bay. The area is of limited extent and forms an irregular S-shaped body whose longer axis is not greater than one mile and whose width is per- haps one-fourth of a mile. It is the body of marble that was first described by Whitney as a feature of the peninsula. The following is a rough analysis of a sample of the purer quality of it:— Car COxe. 97-50% MgC @ pivecncsvusteeseoatccenes 1-60" Hew O arent wel ctatesccoaestslts 35‘ Insoluble residue.............. T. 10" 100.55 % This rock is similar to the white crystalline limestone of Montara Mountain mentioned by Professor Lawson." It occurs also at Santa Cruz, and still more abundantly in the Santa Lucia Moun- tains, extending along the coast south of the Bay of Monterey. Quartzite—At the summit of one of the northern spurs of Vision Hill south of Inverness, there is an exposure of a very hard, dark gray, vitreous rock that under the microscope proved to be a fine-grained quartzite. The grains are small and rounded and closely crowded upon one another. They are quite clear, except that they contain a great many inclusions of iron oxide and other crystalline particles. Small fragments of both biotite and hornblende occur among the grains of quartz. No limestone or calcite was noticed in any connection with this rock, and no evidence of stratification was observed, though both of these might have been found, with sufficient searching. 1y5th An. Rept. U. S. Geol. Sur. 1895, p. 414, etc. Reet a 132 University of California. [Vor. 2. Crystalline Schists—On another minor point of the summit was found a micaceous schist that evidently belonged to the same series, though it was not superficially connected with any other member. This rock is probably a representative of the “‘micaceous slate’? mentioned by Whitney as occurring on the peninsula in some connection with the crystalline limestone. On the shore of Tomales Bay, just north of the point at which the county road turns westward from the shore, there is a still more interesting exposure of rock that belongs with this series. In its general appearance it might be said to resemble a light-colored siliceous schist, and it may not be incorrect to so term it. It over- lies the granite and extends along the shore of the bay for several hundred feet, dipping generally at an angle of about forty-five degrees toward the northeast. The bed is about thirty feet in thickness «and is thoroughly crystalline. It consists of thin layers, ranging from one-fourth of an inch to more than an inch in thickness, which for the most part are alternating leaves of com- pact siliceous material and a mineral which qualitative and micro- scopic tests proved to be mainly wollastonite. The softer layers of the schist dissolve under the action of the weather and leave the siliceous portions standing in high relief. The siliceous part, which perhaps predominates in the exposure, is a fine-grained quartzite, very hard and vitreous, but not sharply separated from the inter- vening layers. Among the grains of quartz of which it is composed are scattered crystals of wollastonite. The grains of quartz are very irregular in shape and are apparently more or less corroded and encroached upon by granular masses of its associate mineral. Under the microscope the quartz grains are seen to be thickly sprinkled with small crystalline inclusions of high refractive power which were not identified. Some of them are hexagonal. Wollastonite seems to be more abundant in the more siliceous portions of the schist, and in portions which contain less silica the wollastonite gives place to tremolite. When tremolite occurs it is in small lath-shaped crystals with an extinction angle gener- ally below twenty-three degrees. It has no crystal terminations. Age of Pre-granitic Series —The pre-granite rocks of the penin- sula deserve much more attention than they have yet received. ANDERSON. ] Point Reyes Peninsula. ities They constitute a remnant of probably the oldest formation in the Coast Ranges of this latitude. There can be little doubt that the series represented here by the limestone, quartzite, etc., is an equivalent not only of a similar group of associates found upon the San Francisco peninsula, but it is also a disconnected area of a terrane more extensive in parts of the Coast Ranges southward. In the Gavilan and Santa Lucia, if not also in the Santa Cruz Ranges, these limestones are conspicuous and have often been reared by orogenic action into prominent white peaks. The crystalline character, the clustered scales of graphite, their associa- tion with quartzites and crystalline schists and with granite, form thus far the strongest evidence of the identity of these metamorphic limestones which form the most important member of the series. Their age has been conjectural, yet the evidence, such as it is, points to a Paleozoic age. Paleozoic sediments of this character are more common on the Pacific Coast than those of any other era. Both at the north and at the south Paleozoic fossils have been found that throw the weight of presumption in favor of this determination. In the Klamath Mountains metamorphic crystalline limestone of Devonian age is found extensively and is characterized by each. of the above features, singularly enough. In Siskiyou County graphite-bearing limestone indistinguish- able from that of Point Reyes is found associated with vitreous thin-bedded quartzite, wollastonite schist, and granite. It is in that region, however, undoubtedly a continuation of the limestone occurring at Gazelle from which Devonian fossils have been obtained." LATER SEDIMENTARY ROCKS. Franciscan Series."—Near the southern boundary of the field, just west of Olema, and on the eastern slope of Whittenberg Hill, there is a small area of dark gray limestone that is thought to be the ‘foraminiferal limestone” of the San Francisco peninsula. It contains a large number of veins of white calcite varying in thickness from one-twelfth to more than one inch. The microscope 1 Am. Jour. Sci., Vol. 147, pp. 416-422. 2 Golden Gate Series of Fairbanks. 134 University of California. [Vot. 2. reveals no definite evidence of organic remains, and it is not certain that they are present. The rock has, however, the usual fetid odor of this limestone, and is associated with a hard, black shale that could well belong to the same series. These rocks seem to rest directly upon the granite, and are adjacent to the zone of crushed granite mentioned in another paragraph. This limestone is appar- ently a continuation of the foraminiferal limestone occurring a few miles to the southeast, where it has been quarried for lime. This is the only body of this series of rocks that has been found within the boundaries of the field, though they occur abun- dantly just outside of it. The series occupies nearly the whole of the east shore of Tomales Bay, and extends to the southward along both sides of the valley, going toward Baulinas. The series, as a whole, seems not to have been greatly affected by the disturbances which have caused so many oscillations of the adjoining peninsula. Miocene Sediments.—The Miocene series consists of three mem- bers, the upper two of which are not distinctly separated. The lower member is a dark, heavy conglomerate, in which the pebbles and stones range from one-half inch to more than one foot in diameter. The second member is a thin-bedded, cream-colored sandstone that passes quite gradually into the upper member, the special features of which will be described later. It is the white Miocene shale of the Monterey series, well known in the Coast Ranges. This series is essentially similar at all the points at which a complete section is to be seen. At the summit of Whittenberg Hill a series of the Miocene sediments, some hundreds of feet in thick- ness, have conglomeratic beds at their base, with a thickness of eight or ten feet, containing pebbles of granite and crystalline lime- stone. On Tomales Point, opposite the Skinner Ranch, a similar series overlies the granites. The conglomerates at this point are not more than two or three feet in thickness. By far the most important occurrence of basal conglomerate is at the southwestern extremity of the peninsula, and especially in the immediate vicinity of the Point Reyes Lighthouse. The axis and southern face of the ridge extending east and west, is of granite. This is overlain along the northern slope by heavy beds of conglomerate, dipping steeply north- ANDERSON. ] Point Reyes Peninsula. 135 ward. At the western end of the ridge, below the light-keepers’ dwellings, and along the shore both at the south and west for a short distance, the conglomerates have a thickness of at least three hundred feet. The dip here is generally about 35° toward the west, though some of it is steeper. The conglomerates here are not of uniform composition, but are made up of large boulders, cobblestones, pebbles, and sand that are very irregularly distributed. The basal portion of the series is somewhat distinct from these conglomerates, although it is appar- ently conformable with them. It consists of a dark sandy shale, about fifty or sixty feet in thickness, that holds its position pretty constantly throughout the whole length of the ridge. It contains a few layers of a calcareous concretionary material, in which search was made for fossils, though without success. This shale rests directly upon the granite, and is overlain above by massive beds of conglomerate. It seemed a little surprising that it should be found in this position, and at first suggested an earlier age, but its regularity and comformability below the conglomerates indicate that it marks only a change of conditions while yet below water level. The conglomerates are evidently shore deposits, while the shales are probably not. The heaviest boulders that were seen in these conglomerates are in their upper portions near the lighthouse, where some of them measure four or five feet in length. There is no ready explanation of this fact, unless we suppose that the changes connected with the formation of these conglomerates were progressive, and in their later stages moved the shore-line only a little farther seaward, thus depositing heavier material upon that which had previously been formed farther from shore. Along the shore of Drake’s Bay, where the granite crops out on the beach, the conglomerates are less than one hundred feet in thickness, and rest directly upon the granite, without the occurrence of the shales that intervene at other points along the ridge. The stones and pebbles of these conglomerates are mainly of granite and quartzite, with an occasional representa- tive of a hard, dark, porphyritic rock and a little slate. Succeeding the conglomerates at all the localities mentioned, are thick beds of sandstone of a light yellowish color. They are 136 University of California. [Vor. 2. moderately coarse-grained and soft, yielding readily to the action of the weather, and are often excavated by the wind into small caves and hollows, On Tomales Point a light yellow sandstone overlies the granite along its eastern border, and in places extends to the water’s edge, along the shore of the bay. At the beach, west of Skinner’s Ranch, an excellent section of the rocks is exposed in the cliffs. Resting upon the granite is a series of sedimentary rocks consisting of (1) a — few feet of coarse conglomerate; (2) a yellowish sandstone, more or less massive, about one hundred feet in thickness; (3) sixty feet or more of whitish, thin-bedded shale. The series is entirely conform- able, and doubtless all belongs to the same period of sedimentation. The sandstones of the peninsula have apparently been derived largely from the granite and consist of coarse quartz sand, scales of mica, and kaolin-like material, all of which diminish gradually as one ascends the series. The dip of the series varies with its loca- tion. On Tomales Point it is about 20° toward the southeast, and away from the cliffs facing the ocean. There can be little doubt that here as well as at the lighthouse ridge a large body of granite has been worn away by the action of the waves. The granitic rocks, lying off shore at both places, give evidence of the same thing. Figure 1.—Section drawn northeast and southwest through Whittenberg Hill. Along the summit of the ridge, west of Point Reyes Station, there are sandstones, similar in character to those already described, overlying the granites and metamorphic limestone. It has here a thickness of about one hundred and fifty feet, which has been well exposed by faulting. The sandstones dip steeply to the west and are overlain in places by remnants of thin-bedded shale, and they probably also extend beneath the white shale that makes up the body of the lower hills lying toward the west. Along the western slopes of Vision Hill and in Bear Valley a similar sandstone occurs ~ in the same relation to the granite and white shale. Along the western shore of Drake’s Bay are sandstones of a loose, crumbling ANDERSON. ] Point Reyes Peninsula. 137 nature, forming the cliffs that are so conspicuous from the mouth of Bear Valley. They are of a light yellow color and are thin- bedded, dipping gently away from the granites and overlying the conglomerates along the northern slope of the ridge. To the northward they pass by insensible gradations into whiter and more shaly material as they ascend the series. On the peninsula the shales cover the larger part of its area, underlying the lower portions surrounding Drake’s Bay and Estero, and composing the lower hills west of the main granitic ridge. In the lower portion of the peninsula they dip at a low angle and are very little disturbed, but along their western margin their inclina- tion is very much greater. They have here been faulted and thrown into a series of short monoclines in which the dip sometimes amounts to as much as 45°. At the summit of Whittenberg Hill the shales have a somewhat darker color than ordinarily, though in other respects they retain their characteristic features. The minute casts of foraminifera are abundant in them and they are composed of essentially the same material as the whiter beds are elsewhere. On account of the peculiarities of their stratification the section at the summit of this hill deserves more than a passing notice. It consists mostly of the finer-grained material composing the main body of the formation, in which are interstratified several layers of a coarse sandy char- acter. These sandy layers, which are usually less than a foot in thickness, form a striking contrast to the strata of finer grain in which they are intercalated. An explanation of this peculiar phe- nomenon is not very easily made. Possibly they have only a ' limited extent and are records rather of fluctuating currents than of any considerable disturbances. Figure 2.—Section drawn east and west just south of White Gulch. It is seen from the above description that the Miocene sediments, lying between the main granite ridge and smaller area at the south- western angle of the peninsula, have been gently folded into a broad 138 University of California. (Vor. 2. syncline, the middle of which is marked by the depression about Drake’s Estero. Along the margins of the syncline the rocks dip steeply, while at its center they are more nearly horizontal. The general axial direction of the fold lies nearly parallel to shore, extending toward the Golden Gate. The development of the fold is doubtless connected with the movements of the block that are discussed in a later section. Petrographic Character.—The petrographic character of the shales which form the principal member of the Miocene series has already been the subject of considerable study at other points of the coast." Nothing of great importance has been discovered on the peninsula, not already known from other regions, and their pet- rography would be merely a repetition of what has been said before. In texture they vary from a tolerably granular, sandy phase to what might be called flinty. In Bear Valley and west of Whitten- berg Hill the compact, somewhat vitreous and banded phase is more frequent, though this appears to be an areal rather than a stratigraphical variation. Such portions of the shale are both less porous and less bituminous than the more granular portions. West of Drake’s Estero the shales are sandy and the amount of bituminous matter is very much greater than in the more compact portions. This is commonly seen in the fetid character of the water rising from them. Origin of the Shales. especial interest, since while they are seemingly unique in character The origin of these shales is of an there are certain homologies between them and other formations with which they have historically no connection. In thin sections and in fresh hand specimens may frequently be seen, even in the porcelanous varieties, small lath-shaped crystals resembling feld- spar. The ashy or pumice-like character of much of the series at Monterey and Carmelo Bays led Professor Lawson to suggest that possibly volcanic eruptions had been the source of most of the material that composes these shales. The hypothesis finds some support in the chemical composition of the shales, which resembles “1 Bull. Dept. Geol. Univ. Cal., Vol. 1, pp. 1-59; Vol. 2, pp. 1-92; Proc. Cal. Acad. Sci., Vol. 1, No. 1, 3d Series. 2 Ate ANDERSON. ] Point Reyes Peninsula. 139 that of an acid rhyolite. This hypothesis, however, could hardly account for the whole of the vast accumulations of sediments that appear to be physically so similar throughout the Coast Ranges, for while there are acid rhyolites found in these ranges, no source has yet been discovered adequate to furnish so large a body of material. On the other hand, it has been urged by Fairbanks’ and con- clusively shown by W. S. T. Smith’ that at least a large portion of the series is of organic origin. The evidences of this derivation are mainly three: (1) The shales are everywhere more or less bitumin- ous. No other source of the bituminous matter is more probable than that of organic remains. Yet fossil shells and bones have not been found in great abundance in them, and therefore the bitumen must have been derived from organisms, the hard parts of which have largely disappeared. (2) Scattered tests and fragments of Diatomaceee and other siliceous organisms have been found in many of the beds, generally in an imperfect state of preservation. These have been most satisfactorily found at Monterey and on the island of Santa Catalina. (3) The colloid nature of the silica, which often forms as much as 90 per cent of the rock, is such as is commonly the result of organic secretion. Samples of the shale tested by W.S. T. Smith, lost by a treatment with potassium hydrate over 70 per cent of their weight. Fairbanks states that in a sample treated by him with the same solvent the loss was as great as 89 per cent of the original powder, which must therefore have been almost the whole of the silica. A sample from the peninsula of Point Reyes obtained from the beach south of White Gulch was subjected to a similar treatment, with the result that all but 26.75 per cent of the powder was dissolved. These tests clearly show the opaline nature of the silica which in these shales usually is either amorphous or has an organic structure. In support of the volcanic origin of a very large part of the series, however, each of the above authors has contributed reliable evidence. On the island of Santa Catalina volcanic tuff is asso- ciated with the Miocene shale. 1 Bull. Dept. Geol. Univ. Cal., Vol. 2, pp. 9-14. “Proc. Cal. Acad. Sci., 3d series, Vol. 1, No. 1, pp. 43-49. 140 University of California. , [Vou 2. In the vicinity of San Luis Obispo,’ according to Fairbanks, the Miocene series has a thickness of 6,000 to 8,000 feet, in which occur beds of volcanic ash several hundred feet in thickness. Thinner ‘ beds of the same material were found in the lower portion of the Miocene series of Point Sal.’ It appears, therefore, to have been satisfactorily shown that the material composing these deposits has been derived in part from both these sources. One of the difficulties met with in the study of the bituminous shales of this series, has been to account for the absence of siliceous organic structures, and the presence of the silica in an amorphous or pulverent condition. Why should there not be a greater abundance of the casts of diatomacez, radiolaria, or sponge spicules, if these have been the chief contributors to the silica of the deposits ? But whatever its source, it is evident, as Professor Lawson has shown, that the silica has undergone a secondary solution and redisposition as a pulverulent or gelatinous silica. This action has been attributed to sea water by both Lawson and Fairbanks. Another agent of solution, however, has been shown to be both more efficient for this purpose and more closely connected with the mass of accumulating organic remains even than the sea water itself. That is the humus acids resulting from the slow decomposition of the soft organic tissues. In a paper by Alexis A. Julien’ it is shown that not only is this a possible explanation of the segregation or concentration of silica into the flinty layers and nodules of chalk, but it is even probably the correct interpretation to be attached to many of the masses of bedded cherts and jaspers in both Mesozoic and Paleozoic rocks. In this connection the author says:— “ The established solubility of silica in solutions of the azohumic acids therefore, suggests that, during the consolidation of the deep- sea sediment, such a solution of disseminated silica by albuminoids and by acids of this character is constantly in progress, etc.” 1Jour. Geol. 1898, Vol. 6, No. 6, p. 562. 2?Bull. Dept. Geol. Univ. Cal., Vol. 2, p. 16. 3 Proc. Am. Ass. Adv. Sci., Vol. 28, pp. 311-410. ANDERSON. ] Point Reyes Peninsula. 141 A similar explanation has been offered for the well-known fact of the silicification of fossils, that is, for their replacement by silica. Professor LeConte has suggested a similar explanation for the silicification of wood." The probable agency of an organic solvent for the silica of the bituminous shales was suspected from an interesting oc- currence on the peninsula. The remains of a cetacean were discovered buried in the bituminous shales of Drake’s Bay. They were encased in an oblong oval crust of compact siliceous matter, which had the general appearance of a siliceous nodule of large dimensions. From one end of this concretion (?) the bones pro- truded, and even these were crusted over with a bead-like layer of opaline silica. There lacks, therefore, no link in the chain of evidence that points to the organic derivation of a large part, if not even the larger part, of the white shales of the Coast Range Miocene. Yet the volcanic source of some of the strata is no less satisfactorily shown. Terrace Formations —The Pleistocene deposits, only a part of which are represented upon the map, are usually coarse arkose detritus with an indistinct horizontal stratification. They are found, generally, in the larger depressions of the peninsula, and range in elevation from 500 feet downward. They form a series of low, broad hills, extending along the middle of the valley near Olema, and occur at intervals upon both shores of Tomales Bay, forming there a system of low bench-like terraces below 200 feet in height. West of the main ridge they are found in occasional patches around the flanks of the hills at the head of Drake’s Estero, and north of Abbott’s Lagoon. Along the county road, crossing the hills, they have an elevation of about 500 feet, and consist of granitic gravels and pebbles of white shales. No fossils have yet been found in them. A beautiful section of these deposits is to be seen in the cliffs east of Drake’s Bay, where 50 or 60 feet of gravels are found capping the Miocene shales. Recent Sands — Along the western margin of the peninsula there are deposits of irregularly stratified or unstratified sand which has 1 Am. Jour. Sci., Vol. 19, p. 181.—Elem. Geol., p. 193. 142 University of California. [Vot. 2. been carried up, and to some extent, sorted by the winds. Along the greater portion of the coast, which is low and rolling, these sands are the ordinary beach sands extending inland for a mile or more, but at two or three points they have a different character, and a considerably greater thickness. At the Pierce Ranch, and still farther north on Tomales Point, there are deposits of fine sand having a brownish color and a much firmer bedding than ordinary beach sand. The short, deep ravines cutting down through them show depths of more than one hundred feet, and appear not to have reached bed-rock at that depth. They contain veins and streaks of iron oxide that have been segregated by the action of the surface water, and these veins stand out in relief upon the faces of the steep sides of the ravines. The eleva- tion of the surface of these sand deposits above sea level is about 300 feet at their highest point. At the northern end of the ocean beach, near the lighthouse enclosures, there are similar deposits of about the same depth and elevation. They consist of the finer and lighter material of the beach wash, which has been carried up by the winds to higher levels. Overwash Gravels.—Deposits resulting from recent atmospheric erosion are not uncommon, and may sometimes be mistaken for the terrace gravels already described. They occur along the lower slopes of the hills and cap some of the sea-cliffs to the east of Drake’s Bay. They have not the regular stratification, though, of marine deposits, and so far as observed have no considerable thickness. Geology of the Farallone Islands.—According to Mr. J. W. Blankinship, formerly a student of the University of California, who visited those islands with Charles A. Keeler, the geology of the Farallones is quite similar to that of the promontory of Point Reyes, being that of a basement of granitic rocks overlain by mass- ive beds of heavy conglomerate. The conglomerate is found along the northern and western sides of the group and was thought to dip northward. Distinct terraces were found surrounding the larger island, but at a lower level than any that were observed 1 Zoe, Vol. 3, 1892, p. 145. ANDERSON, } Point Reyes Peninsula, 143 at Point Reyes. The terrace is best developed on the southeastern margin, or perhaps it may be here only better preserved. STRUCTURE. Crust Block—The peninsula of Point Reyes, including the hilly coastal border south of Bear Valley reaching to Baulinas Bay, constitutes an orographic block that has in its oscillations during later geological periods been largely independent of the adjacent mainland. The eastern boundary of this block is the Baulinas- Tomales depression, which reaches the ocean in the two opposite directions. The submarine limits are not so apparent, though there is no reason for believing that they lie within that of the great sub- oceanic declivity situated but a few miles westward. | How far the block may extend to the north and south may be inferred from facts only briefly considered here, yet such that leave the question not altogether conjectural. The surface of the block is a shallow basin or trough in which rest the Miocene and later sediments occupying the central portion of the peninsula. Evidently the Farallones form one of the outposts of this orographic block and have participated in all of its principal disturbances, which have probably been in accord with those of the Montara block lying south of the Golden Gate. Faults —The evidences of faulting along the Baulinas-Tomales Valley are to be seen both in the topography and in the general. stratigraphic and petrographic relations. East of the valley the long gentle slopes and low rolling ridges of the Franciscan series indicate an old topography, yet the transition to the narrow valley- bottom is abrupt. The western border of the valley is formed by the high, steep ridge of granitic rocks. This ridge is in most places capped by Miocene strata dipping to the westward away from the valley. So far as observed, these Miocene sediments are not to be found eastward of the valley. - Either they have never been deposited there, or, as is more probable, they have been so long above water and subject to aerial erosion that they have been all removed. South of Bear Valley, where the rocks of the Franciscan series are more common, there may be still other 144 University of California. [Vo. 2. evidence. There is also some evidence in the almost rectilinear character and direction of the depression itself. Professor Lawson has described’ a system of faulting on the San Francisco peninsula, separating the blocks of San Bruno and Montara Mountains, the main line of which presents a throw of 7,000 feet, according to estimates made by him. The strike of this fault-line carries it out into the ocean to the west of the Golden Gate. Looking at any good map of the region it is at once apparent that the projection of this fault-line and the Baulinas- Tomales depression almostly exactly coincide. It seems more than probable that the valley and escarpment of Point Reyes penin- sula marks the continuation of the faulting which is so pronounced at San Bruno Mountain. Only rough estimates can be made at present as to the amount of faulting that has taken place along this.valley. We have sup- posed the thickness of Miocene sediments on the peninsula to be not less than 500 feet. The lowest member of the series, coarse gray sandstone, is found capping the granite ridge at an elevation of over 1,200 feet. If the whole of the series were supposed to have been superimposed upon this, with perhaps more that at the present does not exist, and the entire body of this complex series to have been lifted from the level of a few hundred feet below the ocean surface to its present elevation, the amount of the uplift can not have been less than 2,000 feet. Considerable subsidiary faulting has taken place along the escarpment west of the valley. To the west and southwest of Point Reyes Station the system of faulting has been very complex, especially in the vicinity of the small area of “crushed granite” that has been previously described. It is not impossible that Bear Valley owes its origin to some of the minor faults cutting transversely across the ridge. This, however, remains to be proved. The major fault-plane along which the displacement has mainly taken place perhaps lies nearest the western margin of the valley; or, rather, the western margin presents something of the 1r5th An. Rept. U. S. Geol. Sur., p. 468, etc. ANDERSON. ] Point Reyes Peninsula. 145 granitic surface along which the faulting has progressed. The general appearance is that of a normal fault, and there is some specific evidence pointing in this direction. The withdrawal of the Franciscan terrane lying to the east has left detachments of those rocks in somewhat elevated positions upon the flanks of the granite. Similar remnants of Miocene rocks along the western side of the valley opposite Olema also present evidence to the same effect, yet the long succession of oscillatory movements that have affected this region, and of which the present displacements are a partial result, makes it difficult to make accurate statements except of the most general kind. The faulting is evidently complicated as one would expect as a result of complicated move- ments. If there is supposed a downward enlargement of the granitic batholite, then clearly normal faulting has been the most pronounced, as is shown by the rocks lying along the flanks of the granite. The small body of foraminiferal limestone upon the eastern slope of Whittenberg Hill is thought to belong to a low horizon of the Franciscan series, wholly concealed by depression upon the eastern margin of the valley. That there has been, on the other hand, enormous lateral pressure at times, and perhaps accom- panying some of the oscillations, seems evident from the general sheared and broken character of the granite in all parts of the peninsula. This is particularly apparent in the zone of crushed granite lying west of Olema. Lateral compression also seems to offer the best explanation of the synclinal deformation of the Miocene series in the central part of the peninsula between the areas of granite. But if the downward peripheral enlargement of the granite in subterranean levels be supposed, lateral compres- sion could not result in normal faulting, but would produce an overthrust and a consequent depression of the granitic block instead of an elevation. And if the time element in the complexity be considered it may well be supposed that this has been among the phenomena that have taken place. It might, therefore, seem that the successive elevations and depressions of the orographic block, that are to be hereafter described, have had their causes partially in successive compressions and stretchings of the coastal crust. 146 University of California. [VoL. 2. GEOMORPHY. The present relief of the peninsula is not complex and may best be described under the following headings, each of which represents a distinct stage in its historical development, though not all of the stages are included. Main Ridges. cipal ridge following the western shore of Tomales Bay, two points of which attain a height of about 1,300 feet. Between and on either side of these the altitude of the ridge declines. Whitten- berg Hill stands about two miles southwest of Point Reyes Station. The greatest elevations are found in the prin- B Figure 3.—Whittenberg Hill, looking south; Olema on the left, ocean on the right. A It consists mainly of granite mantled over from the west by a tolerably thick monocline of Miocene sediments. Its northern and western slopes are accordingly much more gentle than its southern and eastern, which are rather abrupt. Five miles to the northwest and nearly opposite the head of Drake’s Estero is a more broadly rounded granitic dome somewhat higher than Whittenberg, known as Vision Hill. Its summit is oblong, consisting of a few minor A Figure 4.—Profile of Vision Hill, looking north ; ocean on the left, Tomales Bay Cc on the right. rocky points resting upon a rounded mesa-like platform from which extend a number of bold radial ridges. The summit of this platform probably represents a miniature peneplain. The ridge between these two elevations is a succession of lower summits mainly or entirely made up of granite rocks. ‘North of Vision Hill the ridge is similarly a succession of hills gradually declining in elevation in the direction of Tomales Head. ANDERSON. ] Point Reyes Peninsula. 147 The second ridge that deserves notice is one made conspicuous by its isolation rather than by its elevation. It is at the southwest angle of the field. Its greatest height is about 600 feet, and embraces a limb of the syncline of Miocene strata resting upon the granitic axis. The cliffs facing the south are almost entirely of granite, above which the sedimentary beds rise in a few prominent points. The general level of this ridge is about that of the next topographic feature to be described, though it can hardly be classed together with it. Terraces.—Remnants of two terraces are more or less clearly visible, chiefly west of the principal granite ridge. The higher of these terraces which is much less perfectly preserved than the other is to be traced mainly ina system of rounded hill-tops the general elevation of which is about 600 or 700 feet. They are most satisfactorily seen from the north or south, and are in two groups, the larger of which is immediately east of Drake’s Bay, the other farther to the north. The form of these hills is one that is peculiar to the much-faulted and differently-weathering Miocene sediments of the coastal border. The summits are broadly rounded, the lower slopes are steep, and the hills are separated by long V-shaped cafions. The lower terrace is much more striking in its uniformity and extent. It is one of the clear records of a disturbance very widely felt along the coast north and south. Its general level is about 200 feet or a little more, though its central portion is somewhat lower. This terrace is almost continuous with that of Duxbury Point, and is the one mentioned by Professor Lawson’ as the wave- cut terrace of Point Reyes. It is deeply incised both by narrow cafions descending from the higher ridges, and by the long finger- like extensions of Drake’s Estero, forming a system of lagoons. The central portion of this terrace, in the immediate vicinity of this estero, seems to have suffered a local sagging which has left the land to the westward at a much lower lever than that of the terrace proper. Shore-lines—With the exception of the long sandy beach on 1 Bull. Dept. Geol. Univ. Cal., Vol. 1, p. 245. 148 University of California. [Vor. 2. the western side of the peninsula all the shores are steep or precip- itous. The cliffs bordering Drake’s Bay have a nearly uniform height of 200 feet. On both sides of the northern promontory the cliffs range from 200 to 400 feet in height, and this continues along a large part of the western shore of Tomales Bay. Submarine Topography.—Although there is nothing particularly instructive in the submarine topography immediately bordering the peninsula, yet this body being but a part of a crustal block that is quite extensive it is not amiss to go a little beyond its boundaries for information regarding its orographic history. The maps of the Coast and Geodetic Survey furnish valuable data for studying these problems. Westward from the peninsular border the bottom of the sea slopes rather steeply for a mile or more until a depth of nearly 200 feet is reached, beyond which line the inclination is less than twenty feet per mile to the edge of the great submarine bench, some twenty miles off shore, where the floor plunges suddenly downward. Toward the south, between the Farallone Islands and the mainland, the submarine terrace is still better developed. Its average depth is about 200 feet. Although this portion of the submarine terrace is opposite the Golden Gate, from which issue the waters of the bay of San Francisco with all its drainage, there is but little in its topography to indicate a great accumu- lation of sediments from that source. When compared to the adjoining portions of the terrace north and south, it is approxi- mately a perfect continuation of the same level. A depression or channel extends inwardly between the Farallones and Point Reyes peninsula which possibly marks a former channel of the emboguing river. Essentially this channel accords with the interpretation of this submarine shelf, which regards it as an earlier terrace formed when the land stood at a higher level. 5 Drainage.—The drainage of the peninsula is in two opposite directions and the features of its topography accord with those of the general topographic development. The courses of all the streams may readily be divided into three portions. There are the ordinary steeper cafions at the head, the stretch of narrow gorge with a gentler slope, and lastly a usual stretch of a level ANDERSON. ] Point Reyes Peninsula. 149 semimarsh portion through which the current is ordinarily sluggish. The drainage of the eastern margin is directly into Tomales Bay by short and tolerably rapid streams. That of the western portion is by longer streams, most of which find their way into Drake’s Bay either directly or indirectly. Many of them converge into Drake’s Estero, the outline of which beautifully illustrates the effect of a drowned valley. DYNAMIC HISTORY. Granitic Intrusion.—Evidences of the earlier disturbances of the coast, either epeirogenic or orogenic, are not well shown upon the peninsula. The earliest of which there is any clear record to be found is that of the granitic intrusion into the older crust of sedi- mentary rocks which has resulted in the distortion and metamor- phism of the latter. There is no evidence yet recognized that fixes with any certainty the date of this event. In the absence, therefore, of contradictory facts it may be supposed to be contemporaneous with some of the granites of the Sierra Nevada. At the same time the relatively slight metamorphism of much of the Franciscan (Golden Gate) series, even in actual contact with the granites, makes it evident that the intusion took place prior to the deposition of these rocks, which mark the next epoch of which there is any record here. Subsequent Movements.—After the erosion, which followed the granitic up-thrust, there was a prolonged period of subsidence, during which the strata of the Franciscan rocks were laid down. This event is recorded not only by the small body of limestone and slate found west of Olema, but also by the whole Franciscan ter- rane lying to the eastward of the peninsula. From our knowledge of oscillations that have affected other and neighboring portions of the coast, it would seem that there must have been movements here during the Cretaceous and early Tertiary which have not left legible records. From the beginning of the Miocene, however, our knowledge is more perfect. The character and order of the Miocene deposits show that at the beginning and throughout the Miocene the move- ment of the land was downward. 150 University of California. [Vor. 2. The regular and normal succession of these strata indicate a gradual subsidence and retreat of the shore line, which probably extended considerably eastward of the Olema Valley, as shown by the character of the later Miocene sediments, which could hardly have been deposited near shore, and by the fact also that farther eastward the Miocene is known to occur upon the mainland. Following the Miocene depression was an uplift and period of erosion, during which the strata just deposited were subjected to erosion, the extent of which cannot here be seen. There are reasons, however, for believing it was considerable. Perhaps, also, a portion of the folding of the series took place with this uplift, though it may have been subsequently very much increased. As to the faulting that forms so conspicuous a feature of the topography, it is not known to have had even its inception prior to the close of this post-Miocene land period, but apparently it was connected with the next succeeding movements of the land, the records of which are best known outside of this field. The Plio- cene ‘of the Coast Ranges is known to contain at least two series of deposits, the San Pablo' and the Merced,’ which are unconform- ably related to each other. Both appear to be represented in the near vicinity, though neither of them within the boundaries of the peninsula. Near the town of Tomales are beds supposed to be of San Pablo age, while near Baulinas are others that are probably to be classed with the Merced. If these suppositions are correct, the development of the fault seems to have been progressive from the beginning of the Pliocene. The San Pablo formation is not known to the west of this fault-line, either here or elsewhere, while the Merced seems to be confined in its distribution to the immediate vicinity of the coast. The evidence afforded by this peculiar circumstance seems to indicate that the oscillations of the two -contiguous blocks have been independent throughout the Pliocene, and that the faulting began with a subsidence which covered at least a large portion of the mainland with San Pablo marine deposits. The re-elevation of this block was perhaps accompanied by a ! Bull. Dept. Geol. Univ. Cal., Vol. 2, No. 4; Jour. Geol., Vol. 6, No. 6. 215th An. Rept. U. S. Geol. Sur., pp. 409-476. ANDERSON. ] Point Reyes Peninsula. ISI downward movement of the other, which resulted in an accumula- tion of the Merced deposits of considerable thickness, in its typical locality south of the Golden Gate. Following the Merced subsidence, there was probably a wide- spread orogenic movement, which quite singularly seems to have disturbed and tilted the lately-formed Pliocene strata, without greatly increasing their elevation. The nature of these movements is not very clear, but evidently the land both east and west, that is to say, both orographic blocks, were simultaneously left at a level, considerably below the present one, from which they slowly emerged, forming the terraces previously described, and the corre- sponding deposits of Pleistocene gravels, which have been called by Professor Lawson the ‘‘ terrace formations.” These deposits, how- ever, appear to have been formed only during the earlier stages of the uplift, or rather only the earlier deposits are at present observ- able, the latter being now submerged by a subsequent inundation. The Miocene beds of the peninsula have been deeply scarred by the long-continued atmospheric action, probably in part effected during the period of terracing and elevation, but mainly as it seems at a prior epoch, since the detritus of the terraces is mostly con- fined to the valleys previously excavated. Three quite distinct terraces are recognizable, marking the principal pauses in the process of this elevation. These have already been described, two of which are to be seen along the hills, while the third is entirely submarine. It appears, therefore, that the gradual rise of land which is marked by these benches continued until the shore-line was thrown westward, nearly to the verge of the continental bench, at which time the land must have stood at a level of more than 200 feet above its present position. This is shown by the broad sub- marine terraces just alluded to. From this altitude there has been a sinking, more or less general, which is probably yet in action. This subsidence has resulted in two well-marked effects: (1) The beveling of the submarine terrace, which is in part, at least, due to such causes; and (2) the inundation of the stream valleys, which is illustrated in Drake’s Estero. CNM SE ee 152 University of California. [Vot. 2. SUMMARY AND CONCLUSION. The additions made to our former knowledge of west coast geology by the present study are not great. Aside from the contribution to areal geology they are mainly of the nature of suggestions. An effort has been made to confirm as far as possible by facts gathered in this field, what appear to be. correct conclu- sions reached by studies of other portions of the coast. Diverse conclusions have been reached concerning certain problems here met with, and in so far as the facts observed in this field bear upon them they have been given their due weight. Granite -——The petrographical characters of the granite of the peninsula harmonize essentially with most that is met with in the Coast Ranges southward and with them it forms a more or less satisfactory unit. It differs from the rocks of the Sierra Nevada that have been termed granodiorite both mineralogically and, as far as can be told, chemically. It has its nearest allies in granites of the Klamath Mountains which have not yet been formally described. The age is uncertain but it is, perhaps, contempora- neous with some of the granites, both in the Sierra Nevada and in the Klamath Mountains. If so, it is probably of an age younger than the Mariposa Beds of the Jurassic and earlier than the deposition of the Franciscan (Golden Gate) series. Ancient Crust—The rocks of the pre-granite crust so far as they can be found form a series of limestone, quartzite and a highly metamorphosed crystalline schist. .Their physical and petrographical constants, as far as they can be learned, ally these rocks to the Paleozoic, and there is an analogy between them and certain phases of the Devonian rocks of northern California. Miocene.—Of the later formations only the Miocene has furnished evidence of any important bearing upon lithology. Certain occurrences upon the peninsula are interpreted to confirm the organic origin of the bituminous shales, as was suggested by earlier writers and more recently advocated by Fairbanks. The highly siliceous character of the shales is thus accounted for while at the same time the structureless and amorphous condition of the silica described by both Lawson and Fairbanks is readily ANDERSON. ] Point Reyes Peninsula. 153 explained as a reactionary result of humous acids that are known to originate in the decomposition of organic tissues. The effects of these acids upon organic silica have been the subject of a study by Julien to which reference .is made. The volcanic origin of much of the total volume of rocks in this series (Monterey) is also fully recognized for other portions of the coast. The Miocene sediments lie in a broad syncline resting at both margins upon the granite. Its folding has been affected by move- ments of the orographic block during post-Miocene times which at the same time resulted in a great amount of faulting and the vertical displacement of one of the contiguous blocks to the extent of at least 2,000 feet and perhaps more. Pleistocene deposits are strewn over the peninsula and _ rest generally in an undisturbed position uponall parts, making it appar- ent that the last great movements of the region have affected equally both orographic blocks here referred to, showing plainly that the faulting antedates entirely the Pleistocene Terrace Forma- tions and that it was probably progressive in its development from the opening of the San Pablo epoch, beginning with the subsidence of that time Geological Laboratory, University of California, May, 1899. Me a MP MC PURER Hee Naa IR, ct HoAnme(t” Robe Nah aw a lagy nt hegee | iy 16 6 ? UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology Vol. 2, No. 6, pp. 155-178 ANDREW C. LAWSON, Editor Some Aspects of Erosion Relation to the Theory of the Peneplain. BY W. S. TANGIER SMITH. <> ken She “\ VEp™ ERS Ss ys ly as Z, he > 2 Bz rh SSS Ss Pa ce CANTIED cr ANT? Dae BERKELEY PUBLISHED BY THE UNIVERSITY OCTOBER, 1899. PRICE, 20 CENTS eae EPAU GA ce 06 WTI ( \s UNIVERSITY OF CALIFORNIA. Bulletin of the Department of Geology. Vol. 2, No. 6, pp. 155*178. ANDREW C. LAWSON, Bditor. SOME: ASPECIS) OF EROSION IN REA MON * TO: Toby THEORY OF) THE’ PENEPLAIN.* BY W. S. TANGIER SMITH. CONTENTS. Page APU U GE OMe iia: once ducaskee mee ens alts te eetesaids ontuis cs cede Sacsrh ste suc cis consi nlas snedectne oat 155 Weta mothe: Merny Herepladgen ns ics cer cerastrasdutle etch doses cc's ocioteieotiousensts codons cs 156 Objections! tothe DheonysomPeneplamations.:.csvassesss-tos--2culesecNceceres ape -ces ss 157 Pe MOSeHCe Ol MLeESONG RE eNeplalns msssccuesssseseaseuse ates -otss tneaneevaratecsccsinst a> ser 157 Difficulty of Fulfilling Necessary Conditions.............cscssssceseceeceeseeeeeees 158 ApEn pican Of thie inlicnmee etme Maa taehtad ch cst Redesei aes ses asekeBayecsee cceehee 161 WSerotmtne: MertnyBevel772G:ni.2..-eatessscserch-estiasssens ss Fy Oe RE a eegena tess vedo es 162 Considerations Modifying Use of Term.. ................:0eeeeee a tae 163 Graded! SlOMES cay. we sec tee wecsstenstetosec eens ceteemtebeemen kgs eee AG ask tea ee st 40-6164 Wittenen tial BOTOstOns.ceer- acct e ecu ccieweiwoge se vese hates saseeeseriatiaetunassCe ec areas 166 OnroremiG MOVeMents tsctenccse-begteeesllcceecdneatacceee tee erase sahpsincneacacacoth 171 CDSN GR secon ak nace se etMnat ct Leet a ioeMes docniaaMeny teh atcacttiot adc aciaces teasers 171 SOlltremcteratnce: saaschee vec csees taste oucasubewel es coesesenatesn sah tuls Uuwsttonsbartecstadiets 173 \WGRFETEITI ON ccncde Ibdstindd Ascuno Bed poea Bae ranean BBO Scart ac RO HOHS Roe era ee 173 Conc USlOM emia ec te steas semrediecstine ceca ck shoes Gebetnmbipllcetusesisueds @anasbecibesseewetesacees kits 175 INTRODUCTION. A RECENT article by Prof. R. S. Tarr} has raised a question as to the validity of the theory of peneplains, and at the same time pro- posed a different explanation for the same phenomena, under the *Since this paper was written, an article has been published by Prof. N. S. Shaler (Bulletin of the Geological Society of America, Vol. 10, pp. 263-276, ‘‘ Spacing of Rivers with Reference to Hypothesis of Base-leveling’’), in which he reaches conclusions similar to some of those presented here, though by a different line of reasoning. ‘ + The Peneplain, Am. Geol., Vol. XXI, June, 1898, pp. 351-370. 156 University of California. [Vor. 2, term develing. A later article by Prof. W. M. Davis,* in reply to Professor Tarr, fails (partly through misinterpretation) to meet fully his objections to the established theory, or to overthrow his argu- ments for a new one, and the outcome of the discussion leaves it clear that we should not continue to hold to the peneplain idea without a further sifting of the evidence both for and against it. It remains, therefore, to be determined how far the accepted theory of peneplains may still be applied, and how far the phenom- ena usually classed under that head may or should be accounted for by laws of erosion working under ordinary conditions. To offer some suggestions on these two points is the object of the present paper. DEFINITION OF THE TERM PENEPLAIN. It is well, first of all, to review the definition of this term, since it has been used loosely by some writers. Davis} has defined it as ‘‘a nearly featureless plain” produced by subaerial denudation. The use of the term is thus strictly limited to those topographic forms, whether of local or greater extent, which -are produced by subaerial erosion alone, excluding all other forms of erosion, and all topographic forms due to deposition alone. It is apparent, from further discussion of the term, that the essential point of the defini- tion is the wearing down of the land to an attitude approaching base-level—and therefore no plains, however formed, which do not fulfil this condition, can be called peneplains, even though other- wise similar in character. Finally, although the term does not include plains of submarine erosion or deposition, peneplains formed near the border of a continent would, of necessity, be asso- ciated with these other features to a greater or less extent. The conception of peneplanation on which the following argu- ments are based may be stated thus: the reduction of a limited portion of land, by subaerial processes alone, to a condition of very moderate relief, near ultimate base-level. By “a limited portion of land” is meant here such an area as would form a natural geo- graphical unit. This will usually be a mountain range, or other * The Peneplain, Am. Geol., Vol. XXIII, April, 1899, pp. 207-239. + Am. Journ. Sci., 1889, Ser. III, Vol. XXXVIL fp. 430. won dec nes, TP vVely ei (1 ae i we a SMiTH.] Some Aspects of Erosion. : 157 mountainous area. mS gy koe Yj a = . 0” oo ss BERKELEY PUBLISHED BY THE UNIVERSITY SEPTEMBER, 1900. PRICE, 40 CENTS 7 uN AP Os Cie ct dl a aaa UNIVERSITY OF CALIFORNIA. Bulletin of the Department of Geology. Vol. 2, No. 7, pp. 179-230, Plate 5. ANDREW C. LAWSON, Bditor. A TOEROGRAPHICy Si UDN OF LHERISLANDS OF SOUTHERN CALIFORNIA-* BY %, W. S. TANGIER SMITH. CONTENTS. Page. MiNtFOAUCHONI 0:0. cee eee s0. corsets Petr ioc nciacianeroseerscccee snake cas oaeOslocarsensinmrcesns css 179 Grouping of the ielendss ACH GON IH HEDOOOCE SCE RE a Cee CCE E ET Do nOSaS DUDE CRBEE ECT OH Coane Reo 180 Description of the Islands with Simple Mo pogpaphiyvcrtsccsacsateesres = ocace esses 184 semi soe GmSlandStesauccssseraestorccncrccee-ceseerce teaaetanes ssleaarcaressnocescuscees snes 189 bees inal slan AS. wtenwaceeccns cccccte ses ace eulesmen eee etlsacence ors ces vets tocnslcsie« 195 SUbManinenMeaturesacevcsatecrecccsthcecsccvecnotecsscnstecosieccussabtsesvoscseccrnascecods 196 CoastalaMopogtapiypseecs ccs cteeseesce ewe cecccsdoctessdees socetavcssccecetesssusscacooree 205 Developm entiof iWave-CUty MenraCeShecrasc-ecse oss: encaloleceessisaconcecsicesess coves ecice 208 Preservation of Elevated Wave-cut Terraces .............. Pease coctoncurtsurnsactoesss 216 Nianerandi Current built Meatunesiamecscs-asedvesdescescsetss:.coarcsceascasesaccscseseere 219 MD GOwMedmVallleySeemeetasccste- soe eeee se cceceliccetc scelscnececanscnsesesscesin. | Rb SL ay 2b “13 bs 2 Sees aot 692 iW Cortes Bank 5, 289 \ es 10 " 60 . Sai cally, Bishop Rock 386 Ficure 1.—Cortes Bank and Tanner Bank, former islands, truncated by wave cutting in post- Pliocene times. The soundings are in fathoms. VOL. 2, PL, 5 BULL. DEPT. GEOL. UNIV. CAL Fron U. S. C. & G. S. Chorta, SAN MIGUEL, SANTA ROSA. SANTA CRUZ. = SAN NICOLAS. SANTA BARBARA, eae een SAN CLEMENTE. OSBORN BANK, ‘ SANTA CATALINA. BULL. DEPT. GEOL. UNIV. CAL. VOL. 2, PL. 5 From U. S. C. & G. S. Charte. SAN MIGUEL. JPA. | SAN CLEMENTE. wy ute it a hatte a MW re ede ss p Wao glia SN SmitH.] Tslands of Southern California. 181 stack to San Nicolas. These four islands are widely separated, but each one of them, as well as the group of northern islands as a whole, has a general trend parallel to that portion of the coast to which each is nearest. A submergence of the coast of 100 feet would add to the southern group of islands San Pedro Hill, situated on the main coast to the north of Santa Catalina; while a minimum eleva- tion of about 175 feet would add to the group as islands what are now three submarine elevations known as Cortes, Tanner, and Osborn Banks. Cortes Bank is situated about forty miles southwest of San Clemente, Tanner Bank lying about ten miles to the north of Cortes Bank (see fig. 1). Osborn Bank lies about five miles south of Santa Barbara Island, and has a northwesterly and southeasterly trend, which, like that of the islands in general, is roughly parallel to the neighboring mainland coast. Besides the islands already named, there is a small group, Los Coronados Islands, about ten miles off the coast of San Diego county. An elevation of the coast amounting to 175 feet would join this entire group to the mainland. On account of their size and situation, these islands will not be further considered. Only San Pedro Hill, Santa Catalina* and San Clemente Islands have been visited by the writer. The information concern- ing the other islands is therefore indirect, gleaned in small part from the meager notes which have been published concerning them by the Geological Survey of California, the California Academy of Sciences, and in the various annual reports of the State Mineral- ogist. Nearly all of what follows, however, is based on a study of their topography as shown on the charts of the United States Coast and Geodetic Survey. The islands may be divided topographically into two groups, independently of their geographical arrangement. The one group has simple topography, with comparatively gentle slopes and moderate or slight dissection; the other has rugged, sharply *The study of Santa Catalina (see Proc. Calif. Acad. Sci., Third Series, Geol., Vol. I, No. 1, 1897) was made independently, without any attempt to correlate its features with those of the neighboring land areas. Further inves- tigation has led to some modifications of the views therein put forth, as indi- cated by the statements made in this paper. 182 University of California. . [Vot. 2. incised and serrated forms. The differences are dependent in part on differences in topographic age, and in part on differences in the character of the rocks. Topographic age is estimated by the amount and character of the contrast due to subaerial erosion, allowance being made in this estimate for differences in the resistance of the rocks to, such erosion. Where the rocks are hard, the contrasts will be greater, the subaerial slopes less gentle and the topography more rugged, for a given stage of development, than where the rocks are less resistant. The influence of marine abrasion as a factor in deter- mining topographic age depends upon circumstances. Given an isolated elevated mass, standing on a coast line, or forming an island, wave action, by decreasing the volume of the mass, aids subaerial erosion in bringing the elevation nearer the condition of ultimate base-level, and in this way tends to increase topographic age. On the other hand, when a coast line is depressed, wave action tends to obliterate the contrasts produced by previous subaerial erosion, and to simplify the general topographic form, Therefore, on re-elevation, the youth of the topography will have been renewed, to a greater or less degree, so far as the surface has been brought within reach of wave action. The forms of the Coast Range, in general, approach maturity, and are characterized, for the most part, by narrow ridges and V-shaped valleys. It is generally held by Pacific Coast geologists that these forms belong mainly to the period of erosion following the close of the Miocene, the land then standing at a greater eleva- tion than now. Although the coastal forms are, on the whole, quite rugged, there are many variations in the amount and character of the dissection, due mainly to differences in the resistance of the rocks from which the topography is carved. Some of the forms in the less resistant rocks, especially where isolated, present, compara- tively, very gentle slopes, and are not deeply dissected, although the forms may still be called mature for that particular rock. Along the immediate coast line the more rugged topographic forms do not appear to have been greatly modified by wave action in post-Pliocene times; the less resistant the rocks, the gentler the SmITH.] /slands of Southern California. 183 slopes and the less the contrasts due to subaerial erosion, the greater has been the modification. Most of the islands of southern California present forms similar to those found along the mainland coast, with the variations which would’ naturally result from the differences in the resistance of the rocks, and the possible modification of the forms by wave action during progressive elevation. For this reason it is believed that most of the islands (among which it is intended to include San Pedro Hill, throughout this paper) possessed nearly mature topog- raphy at the close of the post-Miocene period of erosion, this having since been more or less modified (especially in the case of those islands with less resistant rocks) by wave action, and to a less extent by Pliocene and later deposits. Two of the islands with simple topography are exceptional in presenting extremely young topographic forms, their masses not having been elevated till after the close of the post-Miocene erosion period. One of these islands, San Clemente, is developed in hard, the other, San Nicolas, in soft rocks. The rugged forms along the coast and among the islands are always nearly mature and developed in rather resistant rocks. The simple forms, however (as indicated by what has been already given) are either (a) very young, in either hard or soft rocks, or (6) originally mature, or nearly mature, forms, in soft rocks, modified, toa greater or less extent, by later deposits and by wave action. This latter class now presents forms which range from those near youth to those well advanced toward maturity, depending on the amount of modification of the original form. Classifying the islands on the basis already given, we have belonging to the group with simple topography: San Clemente, with extremely young topography in generally hard rocks; San Nicolas, with young topography in soft rocks; San Pedro Hill, with modified mature topography, now presenting, on the whole, the forms of adolescence, developed in moderately soft rocks; San Miguel, with modified mature topography, now rather youthful in character, developed in soft rocks; also Santa Rosa, in part, shows modified mature topography, though belonging, according to its general character, with the more rugged islands. 184 University of California. [Vor. 2, To the group with rugged topographic forms belong Santa Catalina, Santa Cruz, and the larger part of Santa Rosa. Santa Barbara and Anacapa Islands are of doubtful grouping, owing to their small size. It is probable that all of the islands originated through crustal deformation, for the most part as tilted blocks, though with the information at present at hand, it can not be definitely asserted for them all. San Clemente and San Nicolas are without doubt faulted blocks; and Santa Catalina seems to be, in part at least, due to faulting. San Miguel and Santa Rosa, with a minimum depth of water of not more than 100 feet between them, would appear to be a single faulted block, probably modified by differ- ential movements within the mass. Whether the remaining islands of this northern group, Santa Cruz and Anacapa, which apparently forma single unit, originated at the same time and in the same way as San Miguel and Santa Rosa, future field work alone can decide, The remaining island, Santa Barbara, shows no block-like character. Description of the Islands with Simple Topography —Of the islands of the first group, San Clemente has been described by Dr. Lawson* and the writer as a tilted orographic block. It is characterized by gentle slopes on the seaward side and abrupt slopes on the landward side. The seaward slope is marked by an unusually well defined series of terraces, up to an altitude of about 1,500 feet;—a series which (for reasons given later) is unequaled elsewhere on the California coast. On the landward side only fragmentary terracing occurs, where the slopes are locally com- paratively gentle, as toward the northwestern end, where the rocks are folded rather than faulted. Along the steeper parts of this side not even traces of terraces are to be seen. The rocks of the island are for the most part hard volcanics, only a small proportion consisting of less resistant sedimentary deposits. The drainage of San Clemente Island is of post-Pliocene age, *The Post-Pliocene Diastrophism of the Coast of Southern California, Bull. Dept. Geol., Univ. Calif., Vol. I, No. 4, 1893, p. 129. +A Sketch of the Geology of San Clemente Island, 18th Ann. Rept., U.S. Geol. Surv., 1896-97, Pt. II, p. 467. SmitH.] /slands of Southern California. 185 and is still in its infancy. It consists, on the southern side—where well developed—of long, trough-like forms, having a general direc- tion at right angles to the trend of the island, and separated by broad stretches of undissected, terraced surface. Some of the channels on this side of the island scarcely more than notch the terraces over which they flow; few have cut down to sea level. A small lagoon is formed near the mouth of at least one stream, near the southeastern end of the island, which has cut its channel, in its lower reaches, in soft Miocene shale, and in a region of considerable shore drift. The drainage of the northern slope consists of numerous short, steep-graded streams, which have scored this side of the island, in the steeper and higher parts, with comparatively shallow valleys. The description of the general topographic features of San Clemente would apply, with little modification, to San Nicolas, which lies to the northwest of it. San Nicolas differs mainly in size, and in having its fault scarp facing the ocean instead of facing the land. The island is nearly nine miles in length, with a maximum width of three and three-quarters miles. Its highest point is 890 feet in altitude, and lies in the ridge which extends the whole length of the island, nearer the southern side, at an average distance of a mile from the shore. The rocks of the island are sandstone (according to Dr. Cooper { and Dr. Stephen Bowers7), and are therefore readily weathered. Bowers gives the dip as northerly, about 13° to 15°. The gentle slope of the island is toward the north, and this side is distinctly terraced. So far as known to the writer, however, no definite terraces occur on the southern and more exposed side, where, if the development of terraces depended on the power of the waves alone, we should most expect to find them. Cooper has mentioned three “raised beaches” on the island, at elevations of 30, 80, and 300 feet. The flat-topped summit, also, is without * Geol. Surv. of Calif., Geol., Vol. I, 1865, p. 184. } Calif. State Mining Bureau, 9th Ann. Rept., State Mineralogist, for 1889, p. 57 TelcOc. cit, 186 University of California. (Vou. 2. doubt due to terracing. San Nicolas must have been at one time higher than at present, the island having been completely cut away at one stage in the coastal uplift. The same thing is now, again, taking place; for, judging from the submarine shelf on the northern side, the greater part of the island has been cut away in recent geological times, and were the present rate of cutting to continue, it would not be long before the whole of the island, with its records of earlier terracing, would be planed off. (Cortes, Tanner, and Osborn Banks are examples of islands whose tops have been wholly removed during the recent stages of wave- cutting. They will be treated more fully later, under the head of submarine features.) The small number of well-developed terraces found on San Nicolas as compared with the number on San Clemente may be accounted for by rapid cutting in the soft rocks forming this island, the cliffs on the terraced side having been cut back so rapidly that many of the previously-formed terraces were wholly obliterated. The drainage of San Nicolas is much like that of San Clemente. Numerous steep-graded channels score the shorter slope of the island, tending to the formation of cirques; while few, long, narrow and apparently shallow troughs characterize the northern slopes. There are a few indentations on the northern coast, but it is probable that none of them represent drowned valleys of the present cycle of erosion. That the island is a faulted block needs little more proof than its form, which is as definitely that of a tilted crust-block as is that of San Clemente. Below sea-level the contrast between the two slopes is even greater than in the case of San Clemente. The topography of the island has been called young. This conclusion is based not only on the character of the chiseling due to subaerial erosion, but also on the apparently slight modification of the fault scarp,—a striking feature, in view of the fact that the island is composed of soft sandstone, and faces the open ocean, and, therefore, the direction of greatest waves. The abruptness of the fault scarp can not be due wholly to rapid wave-cutting, for the submarine contours show only a comparatively small amount of wave-cutting on this side of the island, and the high angle is SMITH.) /slands of Southern California. 187 continued below sea-level to a depth of at least 300 fathoms. Begg’s Rock, forty feet in height, and lying nine miles north- west of San Nicolas, has been already spoken of as a distant off-shore stack belonging to that island. It lies within the 300-foot ‘submarine contour. San Pedro Hill has been described by Dr. Lawson.* It has a length of about nine and a half miles, and an average width of nearly five miles, its highest part having an elevation of 1,482 feet. The rocks of the hill are largely Miocene shales, and are charac- terized by rather gentle subaerial slopes, showing moderate con- trasts due to dissection. The forms of San Pedro Hill, like those of the Coast Range in general, were doubtless mature previous to the Pliocene depression of the coast. These matured forms have been modified by wave action, which has given rise to a series of well-developed and well-preserved elevated terraces. This modi- fication of the subaerial forms has been greatest at either end of the hill. Near the middle of the hill on the seaward side, and on the landward side, the modification has been least, and the condi- tions most nearly approach the original mature forms. The valleys due to dissection are not deep, nor would they ever, it is probable, become large and open, on an isolated hill of this size, and in rocks of such a character, during the complete physio- graphic cycle. Considering the softness of the rocks of which the bulk of the hill is composed, the general effect of the topog- raphy is seen to be at least that of adolescence. The great terraces on the seaward flanks of the hill are still fresh and young, as terraces, but the topographic age of the surface as a whole, that is, its progress from infancy to old age, is fairly well advanced. San Miguel, the westernmost island of the northern group, lies about twenty-six miles from the mainland, and about three anda half miles west of Santa Rosa, from which it is separated by San Miguel Passage, with a maximum depth, in the middle, of less than 100 feet. So shallow are the channels between all the islands of this group, that an elevation of from 160 to 180 feet would make a single island of them all. *The Post-Pliocene Diastrophism of the Coast of Southern California, Bull. Dept. Geol., Univ. Calif., Vol. I, No. 4, 1893, pp. 122-128. 188 University of California. [Vot. 2. San Miguel has a length of about eight miles, and a width of about four. Its two principal peaks, 861 and 850 feet in altitude, respectively, are situated near the center of the island, and separa- ted by a saddle. From these points the surface slopes gently in all directions. Steep cliffs mark the southern side of the island, rising to a height of from 400 to 600 feet along the middle of this side. For a distance of over three miles on this side there is a low and rather broad platform, the rear of which has an elevation of only forty to eighty feet. The summit of the island is nearer the southern side, and the longer and gentler slopes are to the north. This side of the island is but slightly dissected, and shows only three definite stream courses for its entire length. Since the gentler slopes face the north, and since the open ocean is on the west, we should expect, on the principles set forth later, to find the greatest amount of cutting on the west and northwest; and, judging from the sub- marine contours, this is the case. For the same reason, the best developed elevated terraces, if any are to be found, must be looked for on the same part of the island. The small U.S. C. & G. S. map has rough indications of terraces on the northern side of the island, besides the low platform on the southern side, and a sug- gestion of terracing near the eastern extremity. On the large contoured manuscript map of the U. S.C. & G. S. (scale 1:20,000) this apparent terrace at the eastern end is seen to be at an elevation of 240 feet. North of the island’s center, terrace-like platforms are seen at elevations of 440-480 feet and 520-600 feet. The most pronounced terrace-like structures, however, lie along a line run- ning from the western summit toward the western end of the island. Along this general direction there are nearly level stretches at 220— 240 feet, 320 feet, 480 feet, and 560 feet. At 320 feet the nearly level area has a width from front to rear of over a mile; the interval between the 440- and. 480-foot contours is three-quarters of a mile, and that between the 520- and 560-foot contours is more than half a mile. In all cases these level stretches are marked by a more rapid rise at their rear. These features certainly simulate terracing, and although the above facts are not sufficient for an absolute statement, there is little doubt in the mind of the writer, especially SMitH.] Islands of Southern California. 189 in view of the general topographic character of this side of the island, that these are true raised beaches, cut in very slightly resist- ant rocks, and their outlines softened by erosion. For purposes of the present discussion this will be assumed to be true. Drifting sand is indicated on the map, at the western end of the island, for a distance of about a mile and a half towards the summit; also, to a less extent, at other points. These zolian sands would naturally tend still further to render any terrace features indistinct; but evidently this factor, even in combination with the ready ero- sion of the rocks, has not been sufficient entirely to destroy the terraced character of the topography. The abrupt cliff on the southern side of San Miguel (forming the sea-cliff for the western half of this side, and marking the rear of the 40-80-foot terrace for the eastern half) may or may not be genetically a fault scarp; but its height and abruptness are due, in part, at least, to wave action, undercutting previously formed ter- races, and eating back into the base of the cliff. This conclusion is based on the breadth of the submarine platform on this side of the island, and on the presence of an elevated terrace. Whatever terraces may have been previously formed on this side of the island, were obliterated by the cutting which developed the 40—80-foot terrace, just as this terrace, in turn, has been largely destroyed by the most recent cliff cutting. The Rugged Islands.—Of the islands of the second group, a description of the features of Santa Catalina has been given else- where by the writer.* The main characteristics are the mature and very rugged topography, developed in generally resistant rocks (mainly quartzites and igneous rocks); the leveled character of the summit, at an average altitude of 1,500 feet; the drowning of many of the stream valleys, particularly the largest, at their mouths; the terraced character of the Little Harbor region, this region representing an older, structural valley (with gentle slopes), a con- tinuation of which is shown by the submarine contours; the appar- ent absence of terraces elsewhere. One of these points—the apparent absence of terraces—needs *The Geology of Santa Catalina Island, Proc. Calif. Acad. Sci., 3d. Series, Geol. Vol. I, No. 1, 1897. 190 University of California. [Vou. 2. further comment. In a foot-note in the above-mentioned descrip- tion* the writer mentions the occurrence of rolled pebbles near the southeastern end of the island, at altitudes of 1,000 and 1,400 feet, but considers their character doubtful. It is possible that these rolled pebbles are not shore deposits, but it seems now to the writer hardly probable, especially in the case of those at the 1,000- foot level, which rest on a terrace-like portion of one of the branch ridges running from the main ridge. This branch ridge and the others near it have a roughly terraced character at several points. On the ridge where the pebbles were found, such benches occur at 800 feet, 1,000 feet, and 1,060 feet. The 1,060-foot bench is one of the most pronounced of these, and it agrees pretty closely with the altitude of the corresponding notches on the neighboring ridges. As determined by a hand-level, this bench was a very little lower on the ridge to the north, and a little higher on the ridge to the south, than on the ridge where the pebbles are. On another minor ridge about a mile to the south of this, notching was seen at the altitudes 865 feet, 1,060 feet, 1,300 feet, and 1,400 feet, as determined by aneroid. These benches are not very pronounced, especially as they occur on sharp ridges where they would more readily suffer obliteration than on little dissected surfaces. It is of course possible that some of these readings do not represent defi- nite former ocean levels, but, taking all the evidence into considera- tion, it is improbable that some of them are not true terraces. Further evidence to the same end is to be found in the plana- tion of the summit of the island (in addition to the terracing of the Little Harbor region, already mentioned). This character has been ascribed by the writerf to peneplanation; but more mature con- sideration has convinced him that it could be due neither to pene- planation nor primarily to beveling{, but that it must have been caused mainly by marine abrasion during a depression of the island, and after the present topographic forms had been largely developed. *ICOGNClta ps 12: t Loc. cit., p. 69. tSee, Tarr, The Peneplain, Am. Geol. Vol. XXI,. June, 1898, pp. 351-370, and, Smith, Some Aspects of Erosion in Relation to the Theory of the Pene- plain, Bull. Dept. Geol., Univ. Calif., Vol. 2, No. 6, 1899, p. 162.: SMITH. ] Islands of Southern California. 191 (In support of this view it may be mentioned that a patch of loose, water-worn pebbles was observed at one point on the main ridge near the eastern end of the island.) The summits over the larger part of the island were planed away, leaving a small and nearly centrally situated nucleus, now shown in the two prominent peaks a little to the east of the center of the main division of the island. * Some of the canyons furnish further evidence as to the later movements of the island. The rugged topographic forms of Santa Catalina are, without doubt, of the same age as the coastal forms, that is, mainly belonging to the post-Miocene interval of erosion. In a number of the canyons deposits were formed which have been cut into by the present streams. One of these canyons is a tribu- tary of Avalon Canyon, having a length of about one and one-half miles, with a fall in the stream bed of about 1,300 feet in that dis- tance, thus giving a steep-graded stream, and for the greater part of its length, a narrow, V-shaped canyon. Up to an altitude of 250 feet (as far as it was followed by the writer) the stream has been cutting through earlier deposits to a depth varying from three to eight feet. How much higher the same thing may be found, is not known. Between the altitudes of 150 feet and 175 feet the deposits had a width of about forty feet at the surface (in the narrow, V- shaped canyon), and a maximum thickness of about eight feet. In the center of this deposit the present stream had made a narrow cut several yards in width, and, at most points, down to bed-rock. Practically no impression had been made on the underlying rocks, thus indicating the short time that the stream has been cutting since the deposits were laid down. The rocks do not vary greatly in character for the entire length of the stream course, and, so far as known, there has been no barrier to cause deposits in the bed of the channel. The only satisfactory explanation, therefore, is that of depression since the canyon was cut, followed by elevation caus- ing renewed cutting. This later elevation was prior to the depres- sion which caused the drowning of Avalon Canyon at its mouth. In another V-shaped canyon, in the Little Harbor region, at an altitude of several hundred feet, the present stream has cut through an earlier stream deposit to a depth of about twenty-five feet. At two other points in this same region, but in the broader parts of 192 University of California, [Von. 2. the canyons, similar cutting in earlier deposits has taken place, to about the same depth. The upper limits of the deposits in the Little Harbor region were not determined, but they were noted up to about 300 feet. Santa Rosa, the second in size of the islands of the northern group, is roughly rhombic in outline, with a length of about seven- teen miles, and a width of about eleven. Its main watershed con- nects the eastern and western extremities of the island, bending to the south, and lying considerably nearer to the southern than to the northern coast throughout its length. The minor ridges have a general radial arrangement about the central portion of this divide. That portion of the main divide which forms the island’s crest is a little to the southwest of the center of the island, and runs in an easterly and westerly direction. This region has an average alti- tude of a little over 1,500 feet, a height not even approximated by any other portion of the island. The main ridge here is almost level, having a variation of not more than seventy-five feet for a distance of over three miles. In nearly four miles the variation is less than 175 feet. It would thus appear that Santa Rosa, like Santa Catalina, has suffered planation at an altitude of about 1,500 feet. The southern half of Santa Rosa is quite rugged, with topo- graphic forms closely resembling those of Santa Catalina. In the northern half the summits are broader and platform-like, the general slope is gentler, the relief not so marked, and the whole character is that of forms cut in much softer rocks than those of the southern half. The effect of the whole is of mature topography, the differ- ences being due to differences in the rocks. The softer rocks are less resistant than those of San Pedro Hill, if the character of the dissection may be taken as a criterion. The forms of the northern half, as in the case of San Pedro Hill, have doubtless been more or less simplified by wave action. The topographic age is believed to be not far from maturity for such soft rocks. The general form of the island as a whole is suggestive of a faulted crust-block, though considerably modified by erosion. According to the principles set forth later, pronounced terrac- ing, if it occurs at all, would be looked for only on the gentler, Smitu.] Islands of Southern California. 193 northern slopes of the island. On the small hachured map (U. S. C. & G. S.) of Santa Rosa, the appearance of this half of the island is that of a platform dissected by numerous streams flowing in comparatively open valleys. It would seem that these platform-like areas could be ascribed only to marine action, either deposition or abrasion or both. No very decided indications of terraces, how- ever, appear on the map for this part of the island, except close to the northern shore. At the western extremity and at various points along the northern shore a narrow elevated terrace appears, of the marine origin of which there can be little doubt. The main ridge descends gradually from the island’s crest to the northwest, and along its course are found several nearly level stretches. At about 1,000 feet the ridge is nearly level for over a mile; the inter- val between the 540- and 580-foot contours, along the ridge, is more than half a mile, while that between the 420- and 440-foot contours, near the western extremity of the island, is a mile anda half. The forms near this western extremity are probably more or less modi- fied by drifting sand, as indicated on the small map. Santa Rosa faces the mainland, which is distant only about thirty miles, so that the waves on the landward side have not the sweep that they have in the case of San Nicolas, distant about sixty miles from that part of the coast which it faces. In the case of both islands, the waves from the open sea can strike the northern coast only at a considerable angle. Judging from the submarine contours, the greatest cutting in the case of San Nicolas is on the northwestern extremity, where a low angle of slope is presented toward the open sea. The same is true of San Miguel Island, to the west of Santa Rosa; and the cutting in the case of Santa Rosa would doubtless be more pronounced were it not that the western end of the island is somewhat protected from wave action by San Miguel. Santa Rosa has one broad and open bay, which is not con- nected with the present stream valleys of the island. There are no bays at the mouths of the present stream valleys, comparable in size to the harbors at Avalon and at the Isthmus on Santa Catalina, but this is apparently due to a lack of valleys of sufficient size and devel- opment. The same thing is true of Santa Cruz Island. Small bays 194 University of California. |Vou. 2. similar to the coves of Catalina are found on Santa Rosa at the mouths of a number of the stream valleys, and present evidence of submergence as unmistakable as in the case of Santa Catalina. Lagoons, also, are to be found at the mouths of several of the stream courses, where drifting sand is abundant. Santa Cruz Island, a little to the east of Santa Rosa, is the largest of all the islands of the two groups. It consists, like Santa Catalina, of a larger and a smaller division connected by a narrow neck. The larger division, comprising about two-thirds of the length of the island, has an average width of six anda half miles, the narrower portion averaging about three miles in width. The total length of the island is a little over twenty-three miles. The smaller division, including the neck, has a prominent axis, having the same trend as this part of the island, and nearly centrally situated. It is crossed by a prominent transverse axis a little over three miles from the eastern end of the island. The western and larger division shows two principal ridges, running parallel with the general trend of the island. The northern and higher ridge extends the entire length of this portion of the island, and not far from its middle point is connected with the southern ridge. The latter at its eastern extremity is connected by a short spur with the axis of the smaller division. Along the length of the last two ridges, taken together, we find the following altitudes given for prominent points, on the small hachured map of the U. S. Coast and Geodetic Survey, 1,329 feet, 1,374 feet, 1,406 feet; 1,549 feet. On the northern ridge the altitudes 1,800 feet, 2,407 feet, and 2,144 feet are given. Unfortunately, the writer had access to no larger map of Santa Cruz than this (scale 1:200,000), so that no statement can be made as to the uniformity of altitude of the summits. The northwestern part of the island presents topographic forms closely resembling those of Santa Catalina. The central, southern, and eastern portions, however, show few or no branches on the streams flowing from the main divides, the forms being long, simple, and trough-like. The effect of the whole is of a generally rugged, mature topography, developed in rather resistant rocks. Smith] tslands of Southern California. 195 Goodyear* states that more than three-fourths of Santa Cruz consists of volcanic material. The stream courses of Santa Cruz are well developed and numerous, and many of them show evidence of submergence at their mouths, in the formation of small bays. These flooded stream valleys are more numerous than in the case of Santa Catalina. Nothing is known to the writer concerning possible terracing on Santa Cruz. From the character of the topography it is probable that, if any terraces do occur, they are not well-developed. The chief characteristics of the second group of islands are: a rugged topography; a drowning of many of the stream valleys (when they are of sufficient size and development) at their mouths; an absence of pronounced terracing, which does not preclude, however, some evidence of such features, where comparatively gentle slopes have been exposed to vigorous wave action; and, in the case of Santa Catalina and Santa Rosa, at least, a planation of the summits at an approximate altitude of 1,500 feet. The Small [slands.—Two islands remain unclassified —Anacapa of the northern group, and Santa Barbara of the southern. Although Anacapa is composed of three small islands, these are hardly to be separated, as they lie in a nearly straight line, with very narrow channels between them. They are usually, therefore, considered as a singleisland. The group has a length of about five miles, and a maximum width of a litthe more than half a mile. West Anacapa is the largest, and rises to a height of 980 feet. The chief features of the group are the abrupt cliffs on the south, rising nearly or quite to the summits of the islands, with gentler slopes toward the north. The cliffs are nearly continuous on all sides, but lowest on the north. The rocks of Anacapa are volcanic, according to Dr. L. G. Yates.} According to Davidson’s description and sketch,{ Anacapa is *Calif. State Mining Bureau, 9th Ann. Rept. for 1889, p. 155. +Calif. State Mining Bureau, 9th Ann. Rept. for 1889, pp. 171-174. t The Abrasions of the Continental Shores of Northwest America, and the Supposed Ancient Sea Levels, Proc. Calif. Acad. Sci., Vol. V, 1873-74, p- 93; and Plate V. 190 University of California. [Vor. 2. terraced at an altitude of about 300 feet. Yates* speaks of finding rolled pebbles ‘on the table-land of Middle Island” and also at.one point on Western Anacapa. As Santa Cruz and Anacapa are without doubt genetically parts of the same mass, it is probable that the movements indicated by the terracing of Anacapa were participated in by Santa Cruz. . The northern slopes of Anacapa are not marked by definite channels, except on the western island. Here there are several apparently shallow channels, one of which has a corresponding notch in the shore contour. Santa Barbara has an area of about a square mile, and is roughly triangular in shape, with the base of the triangle toward the east. Parallel to this base, and about midway between base and apex, is the saddle-shaped main axis, from which the surface slopes gently to the east and west. The island is surrounded by cliffs, which reach their maximum height where they cut across the main axis. The eastern slopes are marked by a few small and shallow channels, but none are shown on the west. Cooper f states that this island shows three or four imperfect terraces. He men- tions one in particular, on the eastern side, at an elevation of thirty feet, on which shells are found. This terrace is shown on the map as a narrow shelf at an elevation of forty feet (by the nearest contour). Other terracing, not so definite, is shown both g, on the west and on the east, at elevations of 180 feet and about 280 feet. Santa Barbara is 547 feet in altitude, and, according to the same authority, is composed of volcanic rocks. Submarine Features —Bordering the entire length of the Cali- fornia coast and closely following its general configuration, is a com- paratively narrow submarine platform or terrace, with very gentle outward slopes, and its outer margin, in general, marked approxi- mately by the 600-foot submarine contour. From the outer edge of this platform the descent to oceanic depths is at a greatly increased, though by no means uniform angle. This platform not only follows the general outline of the main coast, but is found surrounding all the islands of southern California. Its width is * oc, Cit. Dp. 1723, 172- { loc. cit:, p.13. SmiTH.] !slands of Southern California. 197 variable. From Point Conception to San Diego it varies from a minimum of about a mile, to the southwest of Point Vincente, to a maximum of ten or eleven miles, found at several points. The usual width is from three to five miles. Along the northern coast of California the descent from the platform just described to oceanic depths is without noticeable break (as shown by the few soundings on the published maps of the U. S. Coast and Geodetic Survey). Between Monterey Bay and Point Conception, however, there is in addition to this, which may be called the upper platform, a second and lower platform, more or less pronounced in its development, the outer edge of which is roughly marked by the 3,000-foot submarine contour. The distance of the 3,000-foot submarine contour from Cayucos is about 43 miles;* from Point Sal 40 miles, and from Point Arguello, 32 miles. Southward to Point Conception the outer edge of the lower platform, like that of the upper one, follows the general direction of the coast line. South of Point Conception, however, the coast makes an abrupt change from the general southeasterly direction which it has been following for more than 500 miles, to a general direction, between Point Conception and San Diego, of east-southeast; while the outer edge of the lower platform still keeps the same general direction as before, to a point about oppo- site the southern boundary of the state, where it, too, makes an abrupt change to an easterly direction. The result is a great curving embayment of the southern California coast line, about 250 miles in length, facing a broad submarine shelf (the lower platform), which has a maximum width in this region of about 120 miles. From the outer edge of this platform the descent is comparatively rapid to oceanic depths of 10,000 to 12,000 feet or more. The depth of the ocean floor, off the Pacific Coast of the United States, varies considerably, showing a gradual decrease as we go northward. Opposite San Diego the depths reached off the coastal platform are from 12,000 to 15,000 feet; while opposite the mouth of the Columbia River the depth is only 9,200 feet at a distance of about 225 miles from the shore. * All distances are given in sta¢wfe miles, unless otherwise indicated. 198 University of California. [Vor. 2. The descent from the upper or lower platform to the ocean floor seems abrupt, on the map, and is suggestive of a great fault or flexure, dying out to the northward. Estimated in degrees, the slope is seen to be very gradual, the maximum being about seven degrees, found at several points off the California coast. In general the slope is considerably less than that, the average probably lying between three and four degrees. The broad lower shelf opposite the embayment of the southern California coast appears to have been an area of great orogenic disturbance, giving rise to many irregularities in the surface form of the shelf. Locally, many parts of this great area are broad and platform-like, but as a whole it is quite uneven, with many depres- sions and elevations. The most pronounced of the latter are, of course, the islands and banks. The marked depressions in this area, as given on the map, are as follows: To the north of San Nicolas Island, at a distance of about twenty miles, there is a depression with a depth of more than 5,400 feet; between San Nicolas and San Clemente Islands, a broad depression with a depth of about 5,700 feet; southeasterly from San Clemente a depression with a depth of more than 6,000 feet; northwesterly from San Nicolas, and near the outer edge of the platform, is a long but not pronounced depression with a depth of about 4,000 feet. On the other hand, there is apparently a broad submarine ridge between San Nicolas and Santa Rosa Islands, with a maximum depth of water of some 1,200 feet. About thirty-five miles south- west of San Nicolas there is a shoaling of the water, to a depth of about 2,400 feet. About thirty-five miles west of the coast of San Diego County is a submarine elevation of considerable size, with a depth of water of from 1,200 to 1,800 feet. Southwesterly from San Clemente Island, and at a distance of about twenty-five miles, another shoaling of the water is indicated by a depth of only 1,944 feet. Cortes and Tanner Banks, and Osborn Bank to the south of Santa Barbara Island, have been already mentioned. Southwest of Cortes Bank, and evidently near the outer edge of the lower plat- form, we find a depth of only 1,770 feet. Considering the upper platform in more detail, for the southern SmitH.] Islands of Southern California. 199 portion of the California coast, the description given by the writer * for the submarine features of Santa Catalina Island would serve as a general description for this entire region. (See fig. 2.) The slope FiGuRE 2.—Submarine profile, southern side of Santa Catalina Island. of the platform is generally least between the depths of 200 and 400 feet. Above 100 or 200 feet the slope is in general a little greater, to the present coast line. Below 300 or 400 feet the slope increases rapidly, being usually more or less uniform, below 600 feet, till the lower platform is reached. These features are not equally well developed at all points, nor in quite the same way. At some points the gentlest grade is between the 100- and 300-foot submarine contours; occasionally the grade is more or less uniform from the shore to a depth of 300 or 400 feet, and exceptionally the rise from the lower platform to the shore line is not marked by any pronounced terrace. The upper submarine platform is believed by the writer to be due to marine action,—in part deposition, though largely abrasion. The conclusion is based on the following reasons: (1) It borders continent and islands alike, and its general characteristics are the same wherever found. Since it follows the general irregularities of . the continental shore line and encircles all the islands, it can not be due to crustal deformation. 2) It is widest in the regions of greatest deposition (e. g., to the northwest and southeast of San Pedro Hill) and of most active cliff-cutting; the latter cases corresponding, in general, to the best development of the elevated terraces. These points of greatest development of both terraces and submarine platform are the salients and the gentler slopes in general. It may be said that the greater breadth of the submarine * The Geology of Santa Catalina Island, pp. 65, 66. 200 University of Cattfornia. [Vol. 2. platform on gentle slopes may be accounted for by considering the submarine slope as simply a continuation of the subaerial slope, since a low grade would normally give a greater distance from the shore line toa given contour than woulda higher grade. But it must be remembered that this platform has in no case (except where deposition appears to be the controlling factor in its forma- tion) the character of a mere continuation of the subaerial slope; it has everywhere the bench or terrace form. This taken in connec- tion with the fact (which will be shown later).that wave cutting is greater on gentle slopes than on steep ones (as the terraces bear witness), and the close correspondence of the platform’s develop- ment with that of the terraces, would go far to establish the origin of the platform through wave action. The platform* as developed about San Pedro Hill is widest off the western and southeastern salients, above which are found the broadest and best developed elevated terraces. In the case of Santa Catalina Island, the platform is wider on the side facing the open ocean than on the landward side (the average width on the landward side being a little over a mile, on the ocean side, nearly two miles). It is, on the whole, wider in the igneous rocks than in the harder quartzites; and it is widest of all on the salients. At the northwestern end of the island the platform has a width of two anda half miles; at the southeastern end, a width of about four miles; and at the salient south of the Little Harbor region, a width of somewhat more than four miles. Along the southwestern face of San Clemente Island, the plat- form has an average width of three miles, while on the northeastern side of the island the average width is about half a mile. The best development of the platform on this side is found near the northern end of the island, where folding in place of faulting has given rise to somewhat gentler slopes. Along that part of the northeastern coast where the fault scarp is most abrupt, the submarine platform is inconspicuous. It reaches its greatest width, for this island, off the salients at either extremity of the island, the maximum being *In what follows the width of the submarine platform is estimated from the shore line to the 600-foot submarine contour, since the position of this contour varies but little from that of the outer edge of the platform. SmitH.] [slands of Southern Caltfornia. 20t off China Point. Thus the development about San Clemente corresponds with that of the elevated terraces, since they are best developed on the southwestern facing, and but little developed on the northeastern side of the island. From a map of San Clemente on which the principal elevated shore lines have been plotted, it is readily seen that during the various stages in the elevation of the island the greatest width of the submarine platform has always been, as now, at the extremities of the island. The platform is broadest on the landward side of San Nicolas, where the slopes are gentle, and narrowest on the abrupt, ocean side, where it averages between a mile and a half and two miles in width. It reaches its maximum width off the salients at either end of the island, being about fifteen miles wide at the end facing the ocean, though considerably narrower than this off the landward end. The submarine platform is wider about San Nicolas than about any of the other islands. This is to be accounted for in part by the greater exposure to wave action, and in part by the softness of the rocks of which the island is composed. The average width of the platform about Santa Barbara Island is between two and three miles. Its greatest development is on the east and west, on the slopes away from the main axis, where the cliffs are lowest. The maximum width is on the west, facing the open ocean. , In the case of all the islands of the northern group, the average distance of the 600-foot contour from the shore is greater on the north than on the south. The slopes of San Miguel Island are most abrupt on the south. The submarine platform reaches a maximum width of some thirteen miles to the northwest of this isiand; while it is narrowest to the southwest of the western end of the island, having a minimum width here of about three miles. The distance to the 600-foot contour on the north of Santa Rosa Island ranges from about five to about eight miles. The platform is narrowest on the southwest, where the range is from two and a half to five miles. The maximum width is to the south- east, where it is probably due to structural conditions. If Santa Rosa and San Miguel Islands together constitute a faulted crust block, as already suggested, with the fault scarp on the southwest, 202 University of California. [Vot. 2. the maximum width of the submarine platform is at either end of the block, while the minimum width is along the fault scarp. The 600-foot contour runs in a northwesterly and southeasterly direction. As shown by the soundings in figure 1 and Plate 5, Cortes, Tanner, and Osborn banks exhibit characters identical with those of the upper submarine platform. They are more or less platform-like in character, and at an average depth corresponding to that of the submarine platform, and the descent beyond the 600-foot contour is generally rapid. There can be little doubt, therefore, that these banks were islands, only a short time ago, geologically speaking, and that they have been completely truncated by wave action during the most recent stages of marine abrasion. If the coastal platform is wave-cut and -built, as the writer believes and as the above details would go to show, then the follow- ing conclusions with regard to the later history of the coast may be drawn from its general character. The broad surface with gen- tle gradient between the 200- and 400-foot submarine contours would indicate a considerable period during which the land stood near one level. This evidence is strengthened by the fact that this in- terval is comparatively wide even where the rocks are hard and the cliffs high and abrupt; for, as will be shown later, cutting along such a coast line is comparatively very slow. The generally steeper slope between the 200-foot contour and the shore line would indicate a much shorter period during which the land was sinking. Whether or not the depression is now in progress can not be stated. These conclusions are in accordance with the evidence furnished by drowned valleys in the case of those islands whose topography admits of such features. The exceptional width of the submarine platform as compared with that of the elevated terraces may be accounted for in part by a prolonged period of wave action at or near one level, as already indicated; in part, also, by the fact that the last formed of a series of terraces is apt to be broader than those previously formed, at higher levels, because each succeeding terrace in cutting back its cliff tends to cut away and obliterate the platform of the terrace next above. ‘ft Wane SmitH.] Islands of Southern Caltfornia., 203 It may be objected that such submarine features as are here described might normally be developed by wave action and coastal currents along any coast line, with sea level nearly stationary for a considerable period. It is to be noted, however, that where cliff cutting is taking place the general features as described are best developed; and where deposition, not cutting, is in progress, as in the embayments, and along those parts of the main coast where wave- and current-built features are forming, the submarine fea- tures depart most widely from the general type. Where shore drift is furnished in comparative abundance, the off-shore depths may be built up rapidly to those normal to the present sea-level Where drift is rapidly removed by waves and currents from a region of active cutting, and in particular along the rugged coasts where cutting is slow and the amount of shore drift inconsiderable, the features in general conform most closely to the description of the whole. It is for these reasons, in addition to the fact of the drowning of the lower parts of the broader valleys, along parts of the island coasts, that the submarine features are believed to indicate a comparatively recent coastal depression. Well-developed beaches are uncommon on the California coast. We should expect them to be more numerous, considering the width of the submarine platform, if the land had stood at or near the same level throughout the time of its formation. If, however, a recent depression of the coast is postulated, the scarcity of beaches is easily accounted for. Since the general characteristics of the upper platform are sim- ilar about all the islands considered here, and along the main coast of this part of the state, it is concluded that the latest recorded movements have been uniform for all of this part of the California coast. Notching the upper platform and its outer escarpment, along the Pacific Coast between San Diego and the Columbia River, are a number of submarine valleys, which have been described in con- siderable detail by Professor Davidson.* Some nine of those de- *The Submerged Valleys of the Coast of California, U. S. A., and of Lower California, Mexico. Proc. Calif. Acad. Sci., Third Series, Geol. Vui. I, No. 2, 1897. 204 University of California. Wer: scribed and figured by him occur within the area under considera- tion. In explanation: of the origin of these submarine valleys on the California coast, two views have been put forward by Pacific Coast geologists—one that they are structural in origin, and the other that they are submerged stream valleys. Neither of these views is wholly satisfactory, especially in accounting for those valleys which head close to the shore line, as the majority of them do. While there can be little doubt that some of the valleys are due to crustal deformation, it would seem that the majority are to be accounted for in some other way—though it by no means follows that this way is the submergence of stream valleys. Further, each valley must be considered by itself, since the explanation for any one is not necessarily the explanation for all. Probably a final and satis- factory explanation can be given, if at all, only after a careful study of the geology in the region about each one of the submarine valleys. The northern group of islands is separated from the mainland by the Santa Barbara Channel, the deepest part of which, forming a basin-like depression, lies to the north of Santa Rosa Island, and has a maximum depth of about 2,200 feet. To the west of that depression a broad submarine ridge extends from San Miguel Island northward toward Point Conception, the lowest part being at a depth of about 1,450 feet. At the eastern end of the channel, between Anacapa Island and San Buenaventura on the mainland, and connecting the upper coastal platform with that of the islands, though at a somewhat lower level, is another short submarine ridge, whose lowest part, about one-third of the distance between the islands and the mainland, shows a depth of water of only 700 feet. As the passages between the islands themselves are in no case of greater depth than 200 feet, an elevation of the coast of a little more than 700 feet would connect the entire group with the mainland. The submarine ridges across either end of the Santa Barbara Channel have doubtless been formed through deposition due to conflicting currents at these points. If caused in this way, both ridges (especially the eastern one) are now and must have been in SMITH. ] Islands of Southern California. 205 the past variable structures, changing with the strength and char- acter of the currents in and about the channel, and with the amount of detritus transported by them. The eastern end of the channel is opposite the mouth of the Santa Clara Valley of the South. During the recent depression of the coast the stream of this valley would have been engaged rather in building up its grade than in corrading its channel. During the post-Pliocene elevation, how- ever, the conditions must have been, in general, different, and during at least a part of that time the stream has been engaged in re-excavating its valley, partially filled during the Pliocene depres- sion. At such times it must have furnished considerable detritus to the neighboring coastal currents. It is not at all improbable, therefore, that at some time (or times) during the later stages of the coastal elevation, when drift was abundant or other conditions were especially favorable, the eastern ridge was built to the very surface of the ocean, so as to make a land connection with, at least, the eastern islands of the group, and afterward broken down by waves and currents during later movements of the land. The broad embayment of the southern part of the California coast had, during Pliocene and a part, at least, of post-Pliocene times, a much greater extent than at present, since it included a broad area of comparatively shallow water, extending from the present coast line inland to the eastward of Los Angeles. Along shore it extended from just north of Santa Monica to Newport Bay. This area, which will be spoken of as the Los Angeles embayment, is now a low plain, bordered by mountains on all sides except the seaward facing; and near the center of its coastal border stands the isolated mass of San Pedro Hill. Coastal Topography—The comparative value of the various factors concerned in the evolution of coastal topography can best be learned from the study of actual occurrences where one or more of these factors, through unusual development, become of prime importance in the formation of certain coastal features, or where, through the variation of some other factor or factors, the factor under consideration becomes of relatively greater importance. Such has been made the main basis for the following conclusions. Owing to the variety of conditions presented, the field under-discussion. is an 206 University of Calfornia. [Vot. 2. unusually favorable one for the study of certain shore features, particularly terraces. The conclusions drawn from the study of the phenomena in this region have been verified, as far as possible, by comparison with other regions of the United States where similar features are found. Gilbert’s classic work* has, of course, furnished most of the fundamental principles involved. The principle which it is desired to emphasize throughout this section of the paper is the dependence of the development of shore features on the character of the subaerial coastal topography. If a given region long subjected to the forces of subaerial ero- sion is depressed, the off-shore slopes will necessarily be those characteristic of subaerial erosion. Along the immediate coast line the subaerial slopes, before depression, will of course have been modified to a greater or less extent through marine action in the process of forming sea cliffs, so that they may present a consider- ably steeper angle than that due to subaerial erosion alone. In any case, however, the erosion slopes will be gentler in the less resistant rocks, and the off-shore slopes after submergence will therefore be less, than in the case of the more resistant rocks. The more resist- ant the rocks to erosion, the greater will be the angle of slope. The least submarine slope will be given by areas of sedimentation, as the floors of broad valleys carried beneath sea level. If, on the other hand, after a long period of comparative quies- cence, a moderate elevation occurs, the immediate on- and off-shore slopes will be those characteristic of the subaqueous platform pro- duced by marine abrasion, and therefore of a very low angle. This is the present condition on the Atlantic Coast, while the former con- dition prevails on the California coast. At the close of the Miocene the California coast was elevated more than at present, in all prob- ability some 3,000 feet. After a prolonged period of erosion it was submerged, and in the rise that followed, the. post-Miocene elevation of the land was only in part recovered. It is therefore assumed that the average on- and off-shore slopes of the California coast are in general those characteristic of subaerial erosion, modi- fied near the present sea-level by a prolonged period of wave action which has formed the submarine platform, or ‘‘continental shelf,” *U.S. Geol. Surv., Monograph I, 1890. Lake Bonneville. SMITH. ] Islands of Southern California. 207 already described. Thus, while the platform itself is due to marine abrasion, its outer scarp presents slopes characteristic of subaerial erosion, modified to a greater or less extent by deposition through marine action. This is believed to have been the condition in gen- eral, also, throughout the post-Pliocene elevation of the coast; that is, that the off-shore slopes, as successive elevations of the land occurred, were largely those characteristic of subaerial degradation, and therefore greater in the more resistant than in the less resistant rocks. Where young subaerial topography is found along a coast line, gentle slopes and slightly dissected surfaces are ordinarily pre- sented, whether the rocks are hard or soft. Exceptionally, such forms may present high, abrupt slopes to wave action, as in the case of a fault scarp facing the ocean. Old subaerial forms are also characterized by gentle slopes and moderate contrasts. Such . forms along a coast line present a variable, though always moder- ate, angle of slope to wave action. Mature subaerial forms present the greatest contrasts, such topography, in rocks of varying degrees of resistance, being gener- ally rugged, as a whole. Where the rocks are hard it will be characterized by a generally bold shore line, with high, precipitous cliffs, though softer rocks will give gentler slopes and lower cliffs, If gentle subaerial slopes with little dissection (and therefore young) are found in the more resistant rocks along such a coast, they can be ascribed only to accident (e. g., faulting). Along the California coastal region, the harder rocks present normally steep and well- dissected subaerial slopes, while the softer ones show slopes of very moderate angle, and usually much less dissected. The gentle slopes found on the slightly dissected ocean facing of San Clemente Island, in rather resistant volcanics, are therefore abnormal and accidental, being due to faulting. With only slight original elevation above sea level, mature forms in rocks of any degree of resistance would differ to a greater or less extent from forms developed in the same rocks with greater original elevation. The matured forms considered in this paper are those resulting from a considerable original elevation, as exempli- fied in the Coast Ranges of California. 208 University of California. [Vou. 2. As a general rule, the gentler the slopes, in a given region, the less resistant the rocks, the gentlest slopes being found in incoher- ent, readily eroded material. The exceptions to this are as indi- cated above, on some very young surfaces. Such very gentle slopes are readily cut by the waves, and usually furnish abundant shore drift. The least shore drift is furnished by abrupt slopes in resistant rocks, such as form a considerable proportion of the Cali- fornia coast. As regards the age of coastal topography, we may have young, mature, or old coast lines characteristic of any given age of the subaerial topography; and the coastal forms of a given age will differ with the age and character of the subaerial forms on which they are imposed. For example, a young coast line in a region of generally young topography will differ in character from an equally young coast line in a generally mature region. Also, since the characteristics of inland topography of any given age differ accord- ing to the resistance to erosion of the rocks in which they are cut, the original amount of elevation of the surface, etc., the coastal forms of a given age will vary to correspond with such differences. Development of Wave-Cut Terraces.—The laws governing the development of a series of terraces on a rising coast must be deduced from a study of the single terrace and the single shore line. Cliff erosion, with the consequent development of a sub- aqueous platform, the principal shore feature with which we have here to deal, is dependent on the action of the waves, concerned principally in erosion, and on the character of the coastal currents, concerned mainly in the transportation of the eroded material. The strength of wave action in cliff erosion is dependent on the direction of the prevailing winds, the distance from which the waves come, the direction in which they approach the shore, and on the character and slope of the bottom, as well as on the amount and character of the detritus along the immediate shore line. The stronger the waves the more active will be the erosion; and the swifter the shore currents the more rapid the transportation of the débris, too much of which acts only as a clog to further cliff cutting. Wave action is greatest, other things being equal, where there is —— SMITH. ] [slands of Southern California. 209 is a moderate off-shore slope. Too low an angle of slope, how- ever, will act as a complete, though temporary, check to cliff cutting, the force of the waves being dissipated over a broad and shallow zone, which must be worn down before cliff cutting can take place. Wherever continuous cliff cutting is taking place, the off-shore slopes must be worn down at the same time, in order that the waves may continue to do effective work on the cliffs. Where the original slope of the bottom is at a high angle, the energy of the waves at first must be devoted to the task of building up the off-shore slopes, before active cliff cutting can take place. Abundant detritus (however derived) is essential to this process. Where such detritus is comparatively scanty (as is the case along the California coast in general), the effective work of the waves in cliff cutting, on a steep slope, would be, of course, very greatly delayed. The conditions might be such, in some cases, that while a comparatively broad terrace would develop on a low slope, no terrace at all would be formed in the same time on a steep slope. It has already been shown that, accidents excepted, the general on- and off-shore slopes are roughly the same, at the outset of terrace development at any given level. With low on-shore angle of slope the sea cliffs are necessarily lower than where the subaerial angle is high—the angle being, as stated, normally dependent on the resistance of the rocks, in regions of mature topography. With waves of equal strength, cliff cutting, even after the necessary conditions are attained (see above), will be slower on the high than on the low cliff, not only on account of the greater hardness of the rocks normally forming such slopes,, but also because, with the high cliff, more material must be cut away and transported for every horizontal foot of cutting; and, since, on the whole, erosion can not exceed the removal of the material cut, the lower the cliffs the greater the advantage in this respect. Asa natural result of slower erosion, terraces developed, on a steep slope will be narrower than those ona gentler slope, other things being equal. High cliffs with abrupt off-shore slopes, even in the case of soft rocks (an exceptional condition in a region of mature topography), will be cut back very slowly, as would follow from the statements already made. 210 University of California. [Von. 2. On a rising coast, where the subaerial and submarine slopes are at a high angle, and the cliffs correspondingly high, the compara- tively narrow terraces formed are more rapidly obliterated through marine abrasion, after uplift, than in the case of a low angle of subaerial and submarine slope, and correspondingly low cliffs, with the resulting broader platforms, provided other factors are the same in both instances. This may be illustrated by the following example. Given two cliffs such that the ratio of the volumes of the material cut in the two cases, for every horizontal foot cut back, along a given length of coast line, is as one to five. This ratio will be given by slopes with a rise of ten feet and fifty feet, respectively, in every hundred feet—corresponding to angles of 5° 42’ 38” and 26° 33’ 54” (angles A’ C’ D’ and ACD in figure): FIGURE 3. To simplify the conditions of the problem, the cutting may be assumed to be in homogeneous rocks, and all other factors except slope (such as character of rocks, fetch of the waves, strength and character of the off-shore currents, etc.) may be considered as the same in the two cases. Further, we may neglect the fact that the sea cliffs are not perpendicular, and also the amount of coastal detritus deposited on the submarine slopes beyond the platform cut by the waves, since neither of these factors (uncertain in any case) would materially affect the general result. Since, at the outset, with the sea-level C’B’/—CB, the submarine slope CD is the steeper, the waves will be longer in making an active start in cliff cutting than on the slope A’C’D’. Although this difference is an important one, it may be set aside for the present, as it will be taken into account later. Considering, then, that in a prolonged period of wave cutting, equal volumes are removed ina given time in the two cases, it follows that when a distance C’B’ of 1,500 feet has been cut in the gentler slope, a Smite] /slands of Southern California. PEM distance CB of, roughly, 675 feet will have been cut in the other slope. If, at this point, an elevation of 100 feet occurs (indicated by the new sea level D’E’—DE), the shore line, for the gentler slope, will be shifted from B’ to D’, a horizontal distance of 2,500 feet €B/C’—1,500 feet, and ID’F’—1,000 feet, for the angle assumed). The shore line of the steeper slope will be transferred from B to D, a horizontal distance of about 875 feet (CB=about 675 feet, DF = 200 feet, for the angle assumed). As before, the waves will be somewhat longer in making a start at D than at D’, on account of the steeper off-shore slope, but this difference in the beginning of the destruction of the two terraces, C’B’ and CB, will be practically offset by the corre- sponding difference at the beginning of their cozstruction, when the sea made its first attack at C’ and C. Since DF is smaller than D/F’ (the ratio being one to five in the example under consideration), and since the altitudes F’C’ and FC are approximately the same, the volume to be removed in cutting back from D to F is less than that to be removed in cutting back from D’ to F’ (roughly one-fifth, in the present case); so that the point F will have been reached by the waves before the point F’ has been reached. After the waves have cut back in both cases to the terrace platforms, C’B’ and CB, the further cutting wiil be at approximately the same rate for both, since the cliffs now have equal altitudes (about 100 feet above sea-level),* and other conditions are the same in the two cases, except that there will be a greater width of submarine platform to be worn down in con- nection with the cliff cutting in the obliteration of the terrace formed on the gentler slope than in the case of the steeper slope. This will offset the corresponding difference in the formation of the terraces. * These first platforms were not level from front to rear, but had a seaward inclination, owing to the abrasion of the platform surface off-shore; so that after elevation the height of the cliffs is less than too feet above sea-level, on the average. This is offset, however, by the fact that in the cutting at the second level the second platform must be worn down by a corresponding amount. 2i2 University of California. [Vor. 2. Since, then, the waves will have cut back to F before they have reached F’, and since the cutting away of the terraces themselves is at approximately equal rates, and since, further, the terrace CB is much narrower than the terrace C’B’ (the ratio of the widths being about 7:15), it follows that the waves will have cut back to the first sea cliff, AB, long before the corresponding point in the other case will have been reached. Thus we conclude that not only are narrower terraces formed where the angle of slope is high, but they are sooner destroyed by wave action, after elevation. The angles assumed in this illustration are such as are not at all uncommon on the coastal slopes of California, in moderately hard and soft rocks, respectively. : As a rule such differences of slope as are shown in these figures would be accompanied by a difference in the resistance of the rocks to erosion. But even if the rocks forming the slope A’C’D’ were much less resistant than those forming the slope ACD, the conclu- sions just reached would not be changed. For, regardless of rock character, if the distance C’B’, with low angle of slope and low cliffs, is equivalent to the distance CB, with higher angle of slope and higher cliffs, then with cliffs of equal height in both cases, CD will have been cut back to BE long before C’/D’ will have been cut back to B/E’. Or, looked at in another way, while a terrace formed on gentle slopes in softer rocks will be more readily obliterated on elevation than one formed on the same slopes in harder rocks, this will be largely offset by the more rapid cutting in the formation of the terrace, which will give a comparatively greater width of platform to begin with. The chief factor in wave cutting Do?) as illustrated above, is the amount of material removed for every foot cut. This depends on the height of the cliff, and this, in turn, depends, normally, on the angle of slope. Hence slope is spoken of as the essential factor, but it must be remembered that it is considered in connection with cliff height. An example of the extent to which the elevated terraces have been obliterated by those formed at lower levels may be taken from San.Clemente Island, where the 80-foot terrace now ranges from nothing to a maximum width of about one-third of a mile. SmitH.] !slands of Southern California. 213 Its outlines are still sharp and clear, but it is only a remnant of its original form; for its width before it had been cut into by, the succeeding lower terraces could not have been greatly less than that of the present submarine terrace, so that we may assume it to have been at least two miles. If, then, the best developed and preserved of the elevated terraces are at the present time compara- tively mere remnants, as on the lower slopes of the ocean facing of San Pedro Hill and San Clemente Island, where the angle of slope was low (5° to 7°), and the conditions in general more than usually favorable to terrace development and preservation, we could scarcely expect to find pronounced elevated terraces, or in most cases even traces of terracing ge, where the original angle of slope was high (25° or more). The present period of wave cutting has been a long one, to judge from the development of the submarine platform, so that there has been ample opportunity for the obliteration through wave action of the comparatively narrow terraces which would be formed on the rugged coast line. This submarine terrace is pronounced off Santa Catalina Island, and in its development cliffs have been produced running up to 1,000 feet or more in height. In any case, it is certain that, whatever height the present actual sea-cliff attains, on that shore no terraces can be found below its upper edge. Other things being equal, cliff cutting is more rapid on the side from which the greatest waves come. That this factor, however, (beyond a certain minimum fetch of the waves which must be assumed in order that they may develop in sufficient size for active cutting) is not so important as the slope of the surface on which the cutting takes place, is seen on San Nicolas Island. Here the side from which the greatest waves come exhibits only a narrow submarine terrace, and no elevated terraces have been recorded on this side of the island; while on the northern or landward side this submarine terrace is of remarkable development (though here best developed where there is the greatest exposure to the waves from the open ocean). In the writer’s opinion, whatever movements may have taken place since the first elevation of San Clemente and San Nicolas, these have been insufficient to prevent the possibility of terracing on 214 University of California. [Vot. 2. the steep faces of these islands. At the present sea-level a terrace of greater or less extent has been developed (see fig. 4) on the 2000 ft 1000 ft FIGURE 4.—Subaerial and submarine slope on the northern side of San Clemente Island, where the submarine platform is least developed. steeper sides of both islands. Further, in the case of San Clemente, elevated terraces are found on the steeper side, toward the north- western end of the island, where the slopes are somewhat gentler. Other things being equal, cliff erosion is more rapid in soft than in hard rocks. The more resistant character of the harder rocks will be somewhat offset by the greater hardness of the cutting tools furnished by its disintegration. But the beach material at any given point may be composed toa greater or less extent of drift from other parts of the coast, in addition to the material of its own cliff This would render the influence of the difference in cutting tools more or less uncertain. The differences resulting from differ- ence in the character of the rocks are seen in the cases of San Clemente and San Nicolas, where the conditions are somewhat similar, except that the gentle slope of San Nicolas faces the land, while that of San Clemente faces the ocean. The submarine plat- form of San Clemente, though broad, is much less so than that of San Nicolas. That a moderate slope, with its consequent low cliffs, and there- fore more rapid cutting, is of more importance (up to a certain limit) than the character of the material eroded, is seen by comparing Santa Catalina and San Clemente Islands, both of which are com- posed largely of hard rocks. San Clemente, with its gentle slope on the southern side, is terraced in a remarkable degree, while Santa Catalina, with its high, sheer cliffs, shows only one pro- SmiTH.] Islands of Southern California. 275 nounced terrace, and that submarine. Further, in the case of San Nicolas, no pronounced terraces have been developed on the steep southern face, notwithstanding the softness of its rocks. Thus marine abrasion in the softer rocks, where the subaerial topography is generally mature, is more rapid, not only on account of the greater resistance of the harder rocks, but also on account of the gentler slopes which characterize the softer areas. Further, given a submergence of both harder and softer areas, the terraces formed on the latter are more nearly continuous (or sooner become so), and therefore more evident to the eye, than those formed on the surfaces of the harder rocks, since the general subaerial dissec- tion is less pronounced in the softer than in the harder areas. If a deeply dissected area of resistant rocks, characterized by steep slopes and V-shaped canyons, is submerged, the terracing will occur at first mainly along the submerged divides, which now form the salients of the coast line. This notching of the crests can never form so marked a feature as continuous terracing even of the same development in other respects, and where such broken ter- races are worn down by erosion their recognition is sometimes very difficult. This will account, in part at least, for the doubtful character of the notching near the southeastern end of Santa Catalina (see page 190). If, in such a case as that just referred to, the ocean remained for a sufficient length of time at one level, the salients would, of course, be cut back, so as to give a more or less continuous terrace. Cutting is most rapid, other things being equal, where the material composing the sea cliffs is most nearly in the condition for transportation, or is most readily brought into that condition, as in the case of a friable sandstone, or a loose-textured rock of any sort. Rapid removal of the material cut away by wave action is essen- tial to further rapid and continuous cutting, the most favorable con- dition being that in which the material is disposed of by currents as rapidly as it is furnished by the waves. It would therefore follow that wherever rapid cutting is taking place, there is also rapid removal of the eroded material. The finer the particles transported by littoral or other currents, or the more powerful the currents, other things being equal, the more widespread will be the 216 University of California. [Vou. z. distribution and deposition of the eroded material, and therefore the less the deposition immediately off shore or along shore. It may be noted here that, in general, the greater the amount of drift passing any given point along a coast line and derived from other parts of the coast, the less rapid will be the cutting at that point; since the drift thus transported must be disposed of by waves and currents, in addition to that derived from the immediately adjacent shore line. A terrace formed during a slow depression will be broader, other things being equal, than one formed during a slow elevation. For, during depression the off-shore depths are slowly increased as the cliffs recede under the attack of the waves, thus avoiding, toa greater or less extent, the continuous submarine erosion otherwise necessary to continuous cliff cutting. On the other hand, elevation only increases the difficulty to be overcome, necessitating more than the normal erosion to keep the off-shore depths sufficiently great for active cliff cutting. It is possible that the width of the present submarine terrace is due in part to a very slow depression of the coast during the earlier stages of its development: From the comparative study made of wave-cut shore features, it appears that, of all the foregoing single factors concerned in the production of pronounced terracing, that of cliff height, normally dependent on slope, is the most important, provided the waves have the minimum fetch necessary for active cutting. Preservation of Elevated Wave-Cut Terraces.—We have next to consider under what conditions terraces, after elevation, best resist the subaerial forces of destruction. If terraces are equally well developed in hard and soft rocks, on surfaces of moderate slope and not greatly dissected, they would be better preserved in the hard rock. For, in order to have equal development in the two cases, it would be necessary, in general, that the slope in the harder rocks should be at least as low as that in the softer; and, with equal slopes, general subaerial erosion (and consequently ter- race obliteration) is more rapid in the soft than in the hard rocks, With equally abrupt cliffs at the rear of the terraces, those in the harder rocks would preserve their sharp outlines for a longer time, those in the soft rocks soon becoming softened and rounded in SMITH. ] Islands of Southern Caltfornia. 217 their outlines. In comparing the terraces of San Clemente, San Pedro Hill, and San Nicolas, their present sharpness is seen to vary with the resistance to erosion of the rocks in which they have been cut. The best preserved and sharpest terraces are cut in the vol- canics of San Clemente, while those cut in the sandstones of San Nicolas have been most modified through general subaerial erosion. The rounding of terrace forms may take place in part through the falling away of the upper portion of the cliff, with deposition of talus at the angle of cliff and terrace, and in part through stream erosion wearing away the upper portion of the cliff, and forming alluvial fans at its base. Terraces are better preserved where they form continuous benches, on little dissected surfaces, than where they are discon- tinuous, forming merely a series of notches on the sharp ridges of a well-dissected surface (in hard rocks). In the latter case, erosion on the slopes of the ridges, by narrowing their crests, soon tends to obliterate the imperfect terraces. At the outset the dissected area is in a condition (as regards the preservation of the terraces) similar to that of the undissected area after a considerable period of subaerial erosion. Where, along the coast line of well-dissected areas of hard rocks, with high angle of slope, the cutting has been sufficient to produce continuous terraces (which will be narrower, as has been shown, than those formed under similar conditions on gentler slopes), these terraces, on account of the more incisive cutting due to sub- aerial erosion in these resistant rocks, will soon become discontinu- ous, and therefore more readily obscured. With cliffs of varying height or platforms of varying width, in a given rock, the higher the cliff or the broader the platform, the longer will the terraced character be evident. Where a narrow terrace with comparatively high cliffs at its rear is developed (in hard rocks), it may soon be buried by detritus from the cliff above, and its character thus be lost. Thus breadth of platform is seen to be more important than height of cliff to the preservation of terrace character. All things considered, then, in a region of mature topography (accidents excepted), a rock of only a moderate degree of resist- 218 University of California. [Vot. 2. ance, with its accompanying moderate dissection and moderate angle of on- and off-shore slope, is best fitted for the development and preservation of wave-cut features. Some of the best developed and preserved terraces along the California coast are in the Miocene shales,* which furnish the conditions just laid down. The principles here stated are illustrated along the California coast generally, as well as on the islands which have been espe- cially considered. Terraces are found well developed in the softer, iittle dissected rocks, where moderate slopes are presented to wave action. They are found little or not at all developed in the more rugged forms, with high angle of slope, characteristic of mature topography in hard rocks; and where developed, they are, in general, but imperfectly preserved. The difference in the character of the topography and evidence of terracing is not, therefore, a certain indication that the two forms have not been subjected to the same conditions, as regards both subaerial erosion and terrac- ing. So that the more recent movements of the islands as a whole have not been the same, can not be predicated from the presence or absence of terraces, so long as the topographic forms are such as to warrant, on the principles already laid down, a terraced structure in one case, and a non-terraced, or but slightly terraced, condition in another. There are many miles of rugged, unterraced topography along the mainland coast of California, adjacent to forms yielding pronounced terraces. The position of San Clemente Island, as regards terracing, is exceptional for the California coast, primarily because of the com- bination of hard rocks with low angle of slope. This combination, on a generally mature coast, could be due only to accident. Through faulting, a very slightly dissected surface of low angle of slope has been presented to wave action in the direction from _which the greatest waves come. As we have thus a combination of the most important factors in both the development and preser- vation of terraces, the natural result is a remarkably well-developed and well-preserved series. *See, Lawson, The Gsomorphogeny of the Coast of Northern California, Bull. Dept. Geol., Univ. Calif., Vol. I, No. 8, 1894, p. 247. Smita. ] Lslands of Southern California. 219 Wave- and Current-Built Features.—The essential factors in the formation of darriers aside from the necessary waves and current —are (1) abundance of drift, (2) gentle off-shore slopes, (3) nearly unbroken shore contour. (1) The chief of these three factors is an abundance of drift, of such size as to be readily transported by shore currents, the supply being continuous and greater in amount than may be readily disposed of off shore by wave and current action. This supply may come from neighboring sources, or it may come from a distance, transported to the point of deposition by shore currents. When so transported, a practically continuous road-bed, either beach, barrier, or embankment, from the point of supply to the point of deposit, is also necessary. This supply of drift may come from the shores through wave cutting, or it may be furnished by rivers, or it may come partly from both sources. In no case can the supply of drift come from the part of the shore where deposition is taking place; for active cutting and deposition can not occur at the same place at the same time. The barrier can persist only so long as the supply of drift is continuous. If this fails, through any cause, the barrier will be cut away, the submarine shelf worn down, and the shore line itself attacked. (2) The steeper the subaqueous slopes the nearer the shore will any wave-built deposit form. For off-shore barriers, therefore, a very gentle off-shore slope is necessary, so that the wave attack may be at a distance from the shore. Such gentle slopes may be normal, or they may have been built up by abundant drift. Where such very gentle slopes occur they can be preserved only by an abundance of drift; for without this the subaqueous slope will be gradually worn down, and the waves will cut back shoreward. (3) A nearly unbroken shore contour for considerable stretches is essential for the development of extezszve barriers. Such a shore contour may be formed originally, as by the elevation of the sub- marine platform, or it may be developed by modification of an uneven shore line through the accumulation of shore drift, where this is abundant. The conditions along the California coast appear to have been very unfavorable to the formation of barriers during the period in which the terraces were formed. The rocks along this coast do 220 University of California. [Vor. 2. not in general yield abundant drift. Extensive incoherent deposits along the main coast are not common, and there are very few streams bringing to the ocean any considerable supply of detritus. The material brought within reach of wave action is in general readily disposed of, so that active cliff cutting is now taking place at nearly all points of the California coast. The same has been true, apparently, during all the time that the terraces were forming. For, along the coast, in general, where the slopes are gentle, active cutting and not deposition is shown by the wave-cut terraces. Where the slopes are steeper and the coast more rugged, though no terracing or only imperfect terracing is found, the conditions must have been still more unfavorable to the formation of wave- built barriers, on account of the steeper on- and off-shore slopes, and the more resistant rocks, supplying a very limited amount of drift. Where barriers have been well developed, and are associated with low landward slopes (as would normally be the case), these features, on elevation, may preserve their chief characteristics for a long time. When built of loose, incoherent material, the forms may be greatly altered by winds, unless soon covered with a protecting mat of vegetation. However, where barriers are not now being developed to any considerable extent, as along the California coast, and where the conditions have been extremely . unfavorable to their extensive formation in the past, such fossil features can not be expected on elevated parts of the coast, espe- cially where the topography is rugged, and the slopes nowhere approach the low angle necessary for their development. In the formation of éars as distinguished from barriers, the first essential is an irregular shore line, for in order to have a bar there must first be an interval to be spanned. In order that a bar may form across any opening or embayment of the coast, the entrance must have a certain width proportioned to the size of the opening itself. If the entrance is narrow and the embayment large, the entrance will not be barred, on a seacoast, on account of the tidal scour. If the embayment is very broad and open, and the water sufficiently deep, the shore drift will follow the coast line, instead of crossing from point to point. SmirH.] Tstands of Southern Caltfornia. 221 Given a suitable embayment to be barred, the most important factor, as in the case of the barrier, is an abundance of material, of a size for ready transportation by the shore currents. The condi- tions with regard to this factor are similar to those already given for the barrier. The formation of the bar is further dependent on the character of the coastal currents, their direction and strength, in relation to each other and to the other factors concerned. With a strong littoral current, sufficient material for the formation of a bar (hook, spit, &c.) may be transported, when with a weaker current the material might be ground up by the waves and disposed of off shore. The bar is essentially a current-built feature, while the barrier is essentially wave-built. We may have a structure built across a very shallow embayment, which, though functionally a bar, 1s gen- etically a barrier, being due to wave action in shoal water. Though these two forms of coastal deposit are typically different, there are all gradations between the two extremes, through different com- binations of the essential conditions on which each depends. A region of mature topographic forms in generally hard rocks, yielding narrow and comparatively steep-graded valleys, and steep on- and off-shore slopes, gives in general very unfavorable condi- tions for the formation of bars. Beaches for the transportation of material will not be numerous or continuous. Detritus will not be readily or rapidly formed, and most of what is furnished will be disposed of off shore. If such a region is depressed, bars may be thrown across the mouths of many of the narrow canyons or of the streams, forming lagoons. These will not be long-lived, being filled sooner or later with sediments brought down by the high- grade streams; or else the embayments may be destroyed through the rapid cutting back of the sea cliffs. ven on such a coast, however, there will probably be exceptions, and favorable condi- tions may be found here and there for the formation of compara- tively extensive bars. It is to be noted that, along a sea coast, a moderate depression, general or local, is usually a condition necessary to well-formed bars, and that during a general movement of elevation, even after a bo bo NO University of California. [vious prior depression, the conditions would tend to grow more and more unfavorable to the production of bars. Since bars are usually formed at the mouths or in the lower stretches of the stream valleys, if these valleys are narrow and com- paratively steep-graded, the bars will soon be removed by the ero- sion of the streams, on elevation, just as the deposits made by the streams themselves during depression are removed on elevation. As the valleys broaden and their grade decreases, the bars formed will tend to preserve their character for a longer time. As their destruction will be due largely to the cutting of the stream which occupies the valley, the length of time during which they will be preserved will depend on the corrasive power of the stream, and on the extent of its wandering to and fro over the valley floor. The general conditions governing the formation and preserva- tion of other wave- and current-built features (spits, hooks, &c.), are similar to those for the features already described, and need not be considered separately. Along the California coast the present conditions are in general unfavorable to bar construction. Large embayments are not numerous, the majority of the drainage lines reaching the ocean being minor ones. Most of the larger openings are too wide and the water of too great depth for the bay to be spanned by a bar; wave- or current-built features may, however, be found in such bays, along the curving shore line, partially or completely closing the mouth of some stream emptying into the bay. San Francisco Bay has its entrance kept open by the powerful tidal currents flow- ing through the Golden Gate. Ina few instances where the cir- cumstances have been favorable well-developed bars have formed, as, for example, at Humboldt Bay and San Diego Bay. Most of the minor valleys have probably not been flooded; but where bays have been formed at their mouths they have in most cases been destroyed, either by rapid cutting back of the cliffs, or by filling in with the deposits of the stream. Some of the larger and more open of these minor valleys are now drowned, without being barred; while a comparatively small number have bars formed at their mouths. Similar conditions to these for the minor valleys are found among the rugged islands off the coast, bars being uncom- SMITH.] Lslands of Southern California. 223 mon features, notwithstanding the fact that some of the canyons are drowned at their mouths. Wherever bars are formed across the mouths of the minor drainage lines, they are in such positions that they might readily be destroyed on elevation. The Los Angeles embayment forms a marked exception to the rest of the California coast. During post-Pliocene times this was, at certain stages, a very shallow and extensive bay, with gentle off-shore slopes, furnishing especially favorable conditions for the formation of wave- and current-built features. Further, owing to the width of this great embayment, and the gentle slopes of its floor, the conditions since elevation are favorable to the preserva- tion of any such features, On the Redondo and adjacent sheets of the Topographic Atlas of the U. S. Geological Survey are seen what appear to be two extensive wave- or current-built embankments or series of embank- ments, within the Los Angeles embayment. One of these extends northward, along and near the coast, from the northern slopes of San Pedro Hill, for a distance of about eleven miles, when it turns to the east, running inland for about four miles, to join an elevated isolated mass southwest of Los Angeles. The structure is not simple, but consists of two distinct, parallel ridges, broad, flat- topped and mesa-like, separated by a series of slight depressions. Of these two ridges, the one nearer the coast has an average alti- tude of 150 to 175 feet, while the average altitude of the other is about 125 feet. The average width of the entire structure is about two miles. The other structure referred to lies at a distance from the coast for the greater part of its length. It begins at the north about five miles east of Santa Monica, and extends, as a low and broad ridge, southeasterly across the entire Los Angeles embayment, a distance of about forty miles. In its course and near its northern end (southwest of Los Angeles) lies the isolated elevation already referred to, the height of which is 517 feet. From this hill the ridge runs to the present shore at Anaheim Landing, about ten miles east of San Pedro Hill. From this point its course is along the shore to Newport Bay, at the southern end of the Los Angeles embayment. The ridge has an average width at its base of, 224 University of California, [Vor. 2. roughly, two miles, and an average elevation of about 200 feet. It is generally flat-topped, and at various points it is modified by terraces at different levels. It has also been cut through at a num- ber of points by the present streams of this region, whereas the first structure described has been cut through at only one point, at the base of the isolated hill already referred to. While it is prob- able that this last-described structure, as a whole, is a former wave- or current-built embankment, it is possible that, in addition to the hill just mentioned, there are other outstanding remnants along its length, for example, Los Cerritos, to the east of San Pedro Hill. So far as known to the writer, no elevated wave- or current- built features occur along the rugged parts of the coast, but those parts of the mainland showing no elevated coastal features whatso- ever are frequently adjacent to areas presenting well-defined terraces or other coastal forms. This, taken in connection with the evidence afforded by the present coast line, in this respect, leads to the con- clusion that the absence of any elevated coastal features, built as well as cut, in areas of rugged topographic forms, is not in itself an indication of a different history from that of a neighboring region where such features are found. Drowned Valleys —If a stream valley is flooded on depression, the amount of the flooding and size of the embayment formed are dependent on (1) the amount of the depression, (2) the width of the valley, (3) the grade of the valley near its mouth; the gentler the grade the greater will be the amount of flooding. The length of time during which a flooded valley remains in that condition depends on (1) the rate of deposition of detritus brought into the embayment by streams or through marine action, as related to the factors above. The smaller the embayment formed, and the more abundant the detritus, the sooner will it be filled. Drowned valleys may be barred at their mouths, forming lagoons which can not always be distinguished from lagoons resulting from a heaping up of shore drift at the mouths of streams which have not been depressed. For although the lagoon formed by depression would have had its bottom originally below sea-level, deposition would have led toa gradual shoaling of the water. The length of time during which a valley will remain flooded depends on (2) the rate of cliff recession, SMITH.] Islands of Southern California. 225 as related to the other factors. The lower the cliffs, the softer the rocks, or the greater the exposure to. wave action, other things being equal, the sooner the embayment will be destroyed. Whether or not a stream valley will be flooded on depression is dependent on (1) the rate of depression as related to the size and grade of the valley, and to the rate of coastal deposition and cliff recession. If the rate of depression is sufficiently slow, the rate of coastal deposition and cliff recession may be such that, for a given coast line, no valleys will be drowned. The broader the valley and the gentler its grade near its mouth, the greater the amount of flooding, and hence the slower the rate of depression necessary to avoid flooding. Thus where valley width and grade vary along a coast line, a given rate of depression, irrespective of rate of cliff erosion and coastal deposition, might drown the valleys of greatest width and least grade, while the narrower and steeper valleys would not be flooded. The flooding of stream valleys on depression is dependent (2) on amount of depression. Where the mouths of the streams are above sea-level prior to depression,—owing to rapid recession of the sea cliffs, or any other cause,—the depression may be insufficient to carry them below sea-level, and in that event there can, of course, be no valley flooding. Broad valleys of low grade, so situated that cliff recession is slow and shore drift scanty, are most favorable to valley flooding on depression and to the continuance of the flooded condition. On the other hand, small and narrow valleys of comparatively high grade, opening on a shore line favorable to rapid cliff recession, or in a region of abundant drift, or where much detritus is furnished by the stream occupying the valley, furnish conditions unfavorable to valley flooding or its continuance. Where, then, along such unfavorable shore lines, no flooded valleys are found, it can not be asserted, in the absence of any positive evidence to that effect, that no depression has occurred. None of the islands belonging to the group with simple topog- raphy give any positive and unmistakable evidence of depression, through valley flooding, since the conditions along their shore lines are unfavorable to that phenomenon. Their stream valleys, either on account of youth or of the softness of the rocks in which they 226 University of California. (VoL. 2. are carved, are small and comparatively shallow, for the most part merely notching the surface just above the shore line. These surfaces, further, have a gentle slope favorable to rapid cliff reces- sion. On the steeper slopes of San Nicolas and San Clemente Islands the stream courses are short and of unusually high grade, and the slight development of their valleys gives conditions still more unfavorable to flooding. Anacapa and Santa Barbara Islands are similar to the islands with simple topography, as regards stream development. Their small size precludes any large streams, and the conditions are therefore unfavorable to valley flooding. The conditions most favorable to valley flooding, among the islands, are found among those with rugged topography. Many of their valleys, as compared with those of the islands in general, are broad and deep, with moderate grade near their mouths. The rocks of these islands being comparatively resistant and their sea cliffs comparatively high, the conditions are also favorable to the continuance of the drowned valleys, especially where the exposure to wave action is least. All of these islands show drowned valleys, those of Santa Catalina being the largest and most pronounced, while those of Santa Rosa, as might be expected from the char- acter of its topography, are the least evident. Thus the evidence from valley flooding is positive on the more rugged islands, and favorable to a comparatively recent depression. Since the evidence on the other islands is merely negative, it can not be stated that they have not suffered recent depression. Judg- ing, then, from the positive evidence of their submarine features,— identical in character with those about the more rugged islands,— it seems that the recent depression has been general for this part of the coast. Historical Sketch.—It is generally assumed that the broad physical features of the Pacific Coast were largely developed during the prolonged period of erosion between the Miocene and Pliocene, and that these forms have been modified more or less by subse- quent movements, both general and local, as well as by subsequent erosion and deposition. During the Miocene the land was depressed, as indicated by the Miocene deposits, the nonconformity between these and the Pliocene deposits showing a period of subaerial SMITH.] Tslands of Southern California. 225, erosion, during which the land was more elevated than at present. This period of elevation and erosion was followed by the Pliocene depression, during which deposits of great thickness were laid down in favorable localities, the larger Miocene valleys being filled to a greater or less extent with deposits which have since been re-excavated to a greater or less extent. During the post-Miocene erosion interval, it is probable that all the islands then differentiated were mountainous masses belonging to the mainland. Judging from their topography, and the apparent genetic relationships of those of the northern group, the forms then existing probably included all the present islands, except San Nicolas and San Clemente. The latter appears not to have been elevated till the close of the post-Miocene erosion period, or early in the Pliocene depression, and it is probable that the elevation of San Nicolas occurred at about the same time. The disturbance at this time seems to have been general for this whole region, includ- ing both faulting and folding, and leading, not only to the differen- tiation of these two islands, but also, probably, to a greater elevation of all the other islands. Although the forces operative in these movements are believed to have acted intermittently from that time to the present, it is thought that they were mainly effective then, and that any later movements have been of minor importance in relation to the general movements of the California coast, since the highest elevated terraces of San Clemente and the leveled summits of Santa Catalina and Santa Rosa still closely correspond in altitude with the highest terraces on the mainland, and, going further north, with the upper limit of the Pliocene delta deposits along the Tres Pinos Creek.* The post-Miocene elevation of the coast was followed by the Pliocene depression, during which the sea stood for a long time some 1,500 feet below its present level, as shown by the highest terraces, the planation of the island summits, and the delta deposits just referred to. Whether this was the full extent of this depres- sion for the southern coast, can not be stated from the evidence at present available. During this depression, at first Santa Catalina, *See, Lawson, The Post-Pliocene Diastrophism of the Coast of Southern California, Bull. Dept. Geol., Univ. Calif., Vol. I, No. 4, 1893, p. 153. 228 University of California. [Vol. 2. San Clemente, San Pedro Hill, Santa Cruz, and Santa Rosa all ‘probably existed as islands, or in the case of Santa Cruz and Santa Catalina, as two or more small islands. At this level the ocean remained, cutting away the tops of these islands, till, in the case of San Pedro Hill and perhaps of Santa Rosa, also, they were prob- ably wholly truncated, leaving submarine banks, like those of the region to-day. It is possible that San Nicolas was also above sea level at that time, and has since been planed off to its present lower level. Of San Clemente there remained a small nucleus, near the center of the northern half of the island. Santa Catalina was reduced to a small island lying to the north of the center of the present larger division of the island, with, probably, one or more distant rocks or smaller islands, toward the present extremities of the island. Santa Cruz, at that time, probably existed as a single narrow island, or a line of islands, with a length of at least seven miles, and formed from the northern ridge of the western or main division of the present island. Then, as now, Santa Cruz was probably the highest, if not the largest, of the existing islands. This depression was followed by a post-Pliocene elevation, as shown both by the present elevation of the Pliocene deposits, and by the elevated coastal terraces. Dr. Lawson* has described one general elevation of the coast in post-Pliocene times, while two such elevations, both greater than the present, and with a depres- sion of 1,200-1,500 feet between them, have been advocated by Dr. Fairbanks.f| A more thorough knowledge of the geology of the coast as a whole can alone decide between these two hypoth- eses. The writer is inclined, from present information, to the view of one general elevation of the California coast in post-Pliocene times, accompanied by minor oscillations, and by local differential movements, such as that called for, for example, in the formation of San Francisco Bay. According to Fairbanks,{ re-excavation *The Post-Pliocene Diastrophism of the Coast of Southern California, Bull. Dept. Geol., Univ. Calif., Vol. I, No. 4, 1893; and The Geomorphogeny of the Coast of Northern California, Bull. Dept. Geol., Univ. Calif., Vol. I, No. 8, 1894. f Oscillations of the Coast of California during the Pliocene and Pleistocene, Am. Geol., Vol. XX, October, 1897, pp. 213-245. t Loe. cit., p. 245. jie a SmiTH.] Islands of Southern California. 229 of the Pliocene valley deposits was largely accomplished during the first post-Pliocene elevation, while the coastal terraces were formed during the second. If the deposits along the Tres Pinos Creek are of Pliocene age,* then, since a well-defined series of stream-cut terraces has been developed in these gravels by the stream which has trenched the present valley, and from the upper limit of the deposits down, a single general elevation since these deposits were laid down would seem to be indicated. For it is reasonable to suppose that these stream-terraces were formed at the same time as the coastal wave-cut terraces; and since sucha series of stream-cut terraces, on the sides of a narrow valley, could not well be formed after the valley as a whole (or even in large part) had been carved, the present form of this valley, at least, must have been developed during the elevation of the coast which gave rise to the series of wave-cut terraces.. The same will hold true for other valleys of the coast where Pliocene deposits have been terraced by stream cutting. It is generally assumed that, to produce terraces along a sea coast, periods of movement must alternate with periods of com- parative quiescence. If variation in movement must be postulated, in order that terraces may be formed during a general elevation, we can not limit these variations to periods of temporary cessation of movement or irregularity in the rate of upward movement, but we must also include the possibility of reverse movements. For, the same causes which give rise to cessation or variation in rate of motion may also be capable of producing reverse movements,—for example, oscillations or movements of depression during a general elevation,—and the possibility of such oscillations must be taken account of in any working hypothesis. Such oscillations would explain the presence of Elephas remains on Santa Rosa Island. For, irrespective of variations in the height of the submarine ridge at the eastern end of the Santa Barbara Channel (see page 204), an elevation somewhat above the present level would be required to connect Santa Rosa with Santa Cruz Island, and thus with the mainland; while a depression on the *See, Lawson, The Post-Pliocene Diastrophism of the Coast of Southern California, Bull. Dept. Geol., Univ. Calif., Vol. I, No. 4, 1893, p. 152. 230 University of California. [Vot. 2. coast below the present sea level would appear to be indicated by the deposits on Santa Rosa in which these remains are found. It should be noted that the only fossil, other than vertebrate remains, which has been described as occurring in these deposits is a fresh-water mollusk (Physa).* It is evident, from the meager descriptions which we have of these deposits, that they should be more thoroughly examined before any definite conclusions con- cerning the latter coastal movements can be drawn from them. It is probable that, while the oscillations of post-Pliocene times have been sufficient to connect the northern islands with the mainland, none of the southern islands have had such connection since the post-Miocene period of erosion. The most recent movement of the coast, as indicated by drowned valleys and submarine features, is a comparatively slight depression, the evidence for which, on the southern California coast, has already been given in detail. The later history of the coast seems, therefore, to be most satisfactorily summed up in a single post-Pliocene elevation, interrupted by minor reverse move- ments, of which this most recent depression is probably one. Whether or not future investigation shall lead to modification of the details of the coastal movements as here outlined, is imma- terial to the main conclusions of the present paper, the principal point which it aims to establish being the fact that the latest gezeral movements of the islands and coast line of southern California have been the same. ~ Oniversity of California, June, 1900. * Am. Geol., Vol. V, 1890, p. 51. _ UNIVERSITY OF CALIFORNIA Bulletin of the Derren of Geology : jh Vol. 2, No. 8, pp. 231-267. ANDREW C. LAWSON, Editor : hele >t f sanity 5 ae Wn AA bly ih ‘N Pit OF he ; Cn ‘a Mig ~ } 2° * ; i . Panama . ee ' : i é i s ; am OSCAR H. HERSHEY. é: 4 ; ae \ sal \ g f Ree is Ve i iS Fen ‘4 - 1S), S “ , “ ee. a 20 y i . ; * “ey, on 4 CES Aids ‘ $ Bs. ra Ponceau : IZM 2 ue ak BERKELEY | one Z PUBLISHED BY THE UNIVERSITY base ‘ MARCH, 1901. PRICE, 30 CENTS UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology Vol. 2, No. 8, pp. 231-267 ANDREW C. LAWSON, Editor THE: GEOLOGY OF THE CENTRAL PORTION OF THE ISTHMUS OF PANAMA. BY Oscar H. HERSHEY. CONTENTS: Page MmMEKOCUCtION, Sracarsastccoitonceesssetedass sgeosccrousdacisssse cca ncevasdeieaedsacacenaraucssieces 232 PAT EARSTUGIER! sicsadcececoced cboqeneseeoscctaciers eeme seamen tetas sesacerscorsstscoscnecse tices 233 “TN OIDOPATEIO ONY cesos.cdadoo spdiutice ones4dabi00) copadbods ceeeab UNE aCe SoO don HUCCHn Don COuGe CEE CBee 234 Rogmations® Earlier Dhani the: PleiStocene:......c-...0-.cscosceesseeeoaocrescscasesuccees 237 Pah ePAZUErOVMOLMatlon! jy. cscrhsseccidevees taller «cteevGeeestscecosssenesacesteesacesesens 237 sWnewROniOMBIMestomec es tesa rice celmertecrcitaseces sesh desedactesecedcocessansecsns 239 pbhes Montijo, Conclomeraterc..-c.ccersevesascccst ecctsenes dascssesspessesesseeses cesses 241 Mer Santia SOP MOLMaAtlOMy. cerecccestsccestoelscsecises > acecseeares cospemsteuscasessasalace 241 hhemertianye basalt CONClOMETATE....ccs.s- Tater-Extinct Floras, p. 85, pl. LVI, Bic. ie VEIL Tiga t. £898.[1890 |. Platanus aspera Newb. Hlatanus sp. Crategus flavescens Newb. Myrica diversifolia Lesq., Cret. & Tert. FI., p..241, pl. L, Fig.-10, 1883. Grewra ermata Newb. Fraxinus integrifola Newb. ROAD-CROSSING AT CHERRY CREEK. [Locality Soq.] Asplenium substmplex (Lesq.) Kn. Lygodium kaulfusi Heer. Lquisetum oregonense Newb. Juglans rugosa Lesq. Flicoria? Nn. sp. Rhamnus cleburni? Lesq. Fragments. ONE AND ONE-HALF MILES EAST OF CLARNO’S FERRY. [Locality 832. ] Sequoia langsdorfi (Brgt.) Heer. Alnus corrallina? Lesq. Alnus carpinoides? Lesq. Olmus? Sp. Acer sp. Fragments. THREE MILES ABOVE CLARNO’S FERRY. [Locality 84o.] Equisetum oregonense Newb. Zizyphus longifolia? Newb. Aralia sp. Aralia? Fragments, 290 University of California. [VoL. 2. ONE-HALF MILE NORTHEAST OF FOSSIL. [Locality 844.] Sequoia langsdorfi (Brgt.) Heer. Alnus carpinoides Lesq. Myrica? n. sp. Fragments. “In attempting to work out the bearing of the plants above enumerated on the question of the age of the beds, it should not be overlooked that any conclusions drawn might be quite different from what they would be were the whole flora of each of the locali- ties to be considered. For example Dr. Merriam’s collection from Bridge Creek embraces only fourteen previously named species, whereas the complete known flora of this locality includes over forty species. And further it is impossible at the present time, without having worked out the affinities of the Tertiary floras of California and elsewhere, to give with any degree of completeness the outside relationships of the flora of the John Day region. The following conclusions, however, are not likely to be greatly modi- fied by subsequent work. “The oldest horizon represented by these collections seems to be that near the crossing of Cherry Creek [loc. 804]. The species though few in number seem to have their greatest affinities with forms from the lower Tertiary, and it is probable that this horizon should be referred to the lower or middle Eocene. There area few species in common with Bridge Creek but in general its flora has a slightly older facies. “ The Bridge Creek [locality 811] as already suggested has an ample flora which is represented by a wealth of individuals. A large proportion of its species are endemic but on considering the ovovious relations of these, as well as the forms known from other localities, an upper Eocene age is indicated. “ Several other of the localities seem to be of the same age as the Bridge Creek beds, namely: one and one-half miles east of Clarno’s Ferry [loc. 832]; three miles above Clarno’s Ferry [loc. 840]; and one-half mile northeast of Fossil [loc. 844]. Not more than three previously-named species are known from either of these localities, a MrrRiAM.] John Day Basin. 291 and not rarely the identification of some of these is more or less doubtful, but as nearly as can be made out they should be of the same age as Bridge Creek.” It will be noticed that the determination of the plant remains, both as regards the flora as a whole and with respect to its sub- divisions, agrees with the statement relating to stratigraphic suc- cession. The Bridge Creek beds, with the few specimens from the shales one and one-half miles east of Clarno’s Ferry, are considered upper Eocene, while those from Cherry Creek are held to be an earlier facies. JOHN DAY SERIES. Resting upon the Clarno formation and extending over the greater portion of the John Day basin, is a thick series of sedi- ments which Marsh* called the deposits of the “John Day Lake.” It has generally been referred to in geological and paleontological literature as the John Day beds. Kingt correlates this series with his Truckee beds as a part of the deposit of his Pah Ute Lake. In the statement regarding this correlation, King has, however, recog- nized Marsh’s name, so that, if a correlation is attempted, Pah Ute should be displaced by John Day. General Characters—Nearly the whole of the John Day formation consists of ashy or tufaceous materials. Only toward the top of the section do we find typical products of ero- sion. At Haystack, Spray, and in the lower end of Turtle Cove, good exposures show the highest portion of the series to be com- posed of one or two hundred feet of hard, blocky tuff, below which is about the same thickness of sand and gravel. The gravels are in some places quite coarse, containing pebbles four or five inches in diameter. The sands sometimes show cross-bedding. Included in these deposits are worn fragments of bones and teeth, which probably represent forms similar to those in the beds immediately below. Rhyolite flows are found toward the lower part of the Middle John Day at Bridge Creek, near the top of this division in Turtle *O. C. Marsh, Am. Jour. Sc., 1875, 2d Ser., Vol. 9, p. 52. +C. King. Survey goth Parallel, Vol. 1, p. 458. 292 University of California. [Vor. 2. Cove, and overlying what is probably Middle John Day on Pine Creek, about three miles northwest of Spanish Gulch. The tuffs and ashes seem in some cases to have been worked over somewhat by air or water. At other points, beds many feet thick have apparently been deposited directly, without much, if any, working over by either wind or water. The source of the ash and tuff is as yet unknown. It probably came from vents not very distant from this basin of deposition. Excepting the beds of sand and gravel near the top of the section, the stratification throughout the whole thickness of the John Day is very regular. Numerous beds of almost pure ash or tuff compose uniform, hard, and prominent layers, between which in the softer beds the regular deposition of thin layers is plainly indicated by delicate variations in color. Nodular layers, possibly produced in part by contained organic remains, are not infrequent in some localities, and small nodules are usually scattered through a large part of the Middle John Day. The erosion forms and coloration of the John Day strata are quite characteristic when compared with those of other formations in the basin. In general the beds are colored various shades of red, green, blue, or yellow. In some cases they are white or gray. As will be shown later, the coloration is an important character in distinguishing the subdivisions of the system. The beds are usually quite soft and disintegrate very rapidly, forming a layer of mud several inches thick over a large part of the exposed surface. A moderately heavy rain starts the mud almost in streams, and, as it is soon formed again, erosion must proceed very rapidly. At several localities visited by the writer, groups of unrelated bone fragments, evidently brought together. by collectors, were found resting on small pinnacles several inches in height, showing that in ten to twenty years erosion had progressed at least four or five inches in fairly favorable localities. In the Lower John Day the tendency of erosion is almost always to produce dome-like, mud-covered hills, with scarcely a fragment of the bed-rock protruding anywhere. In the middle division steep, pinnacled bluffs, exhibiting beautifully the typical bad-land_ structure, are common, and in the uppermost division they are the rule. MERRIAM. | John Day Basin. 293 Without having accurately measured the John Day section, the writer would not be willing to consider the exposures north of the southern range of mountains as representing a ‘thickness much greater than 2,000 feet. Perhaps it is not more than 1,500 feet thick. At Sheep Rock, near Picture Gorge, the whole section is shown rather sharply tilted, and all but the lower division would be included in the column between the cap rock and the level of the river. At Bridge Creek, also, the section includes the whole of the series. It may reach a thickness some- what over 2,000 feet at that locality. Classification on Basis of Lithologic and Stratigraphic Characters. —Owing to the importance of determining the vertical range of the fossil forms contained in this series, it has been desirable to find some marks of recognition, besides purely palaontologic charac- ters, by which the beds of widely-separated sections may be correlated. Though no sharply-defined dividing lines can be drawn inside the series, it is still possible, on the basis of both palaonto- logic and lithologic characters, to subdivide it into several fairly well-marked divisions. Wherever the John Day is well exposed in the central and western portion of the basin, it seems to be divisible into three stages, which have been designated * the Lower, Middle, and Upper John Day. The lower division consists usually of highly-colored shale, which breaks down readily, forming characteristic mud-covered domes. These beds are in the main a deep red, with occa- sional alternating strata of buff or white ash. At Bridge Creek alternating beds of red, white, and green, occurring in a group of the typical hills of this division, form a striking feature of the landscape, the colored strata making sharply-defined rings about the hills. At Clarno’s Ferry numerous alternations of con- torted and faulted, red and white beds are splendidly exposed in prominent hills at the bottom of the section. The beds of this group appear usually to show more deform- ation than those higher up in the series. This may be due in part *Science, New Series, Feb., 1900, Vol. XI, p. 219. 294 University of California. [Vou. 2. to their being softer and having offered less resistance to disturb- ances than the more rigid strata above them. The Lower John Day is almost barren of fossil remains at all points where it was visited, and has never, so far as ‘can be dis-. covered, furnished many good specimens. Diligent search by the writer at several localities has been rewarded by the discovery of two or three fragments of rhinoceros teeth. An Oreodon skull was found at this horizon, many years ago, by Mr. L. S. Davis, but definite information regarding it is not now obtainable. The lower division was estimated to be 250 to 300 feet thick at Clarno’s Ferry. Its maximum thickness will probably exceed that limit. It is not impossible that the Lower John Day will sometime be found to be separated by an unconformity from the middle division. Such fossil remains as have so far been found in it indi- cate, however, that it belongs to the John Day series. The middle portion of the John Day section at Bridge Creek, Clarno’s Ferry, and Turtle Cove, consists of drab to bluish-green beds, sometimes forming rounded hills, but more frequently exposed as steep, pinnacled, and ribbed bluffs. Nodular layers and thick beds with small nodules scattered through them are common in this group, while they are rare, if not entirely absent, in the lower division, and are not common in the uppermost beds. The strata of this group are never so sharply contorted as those of the lower division, though they may stand at a fairly high angle and may show considerable faulting. This stage has probably furnished more fossil remains than the upper division, partly because the remains are here frequently found in hard nodules, which have protected the bones and held them together. At Bridge Creek a rhyolite flow is interbedded with the lower part of the Middle John Day, or possibly separates it from the lower division. In Turtle Cove a similar flow is found at the top of this division and possibly separates it from the upper group. At many places, particularly in Turtle Cove, hard beds of white to greenish ash and tuff are intercalated between the softer and usually more fossiliferous strata. (See Fig. 2, Pl. 7.) The middle division is at least 500 feet thick in Turtle Cove, and possibly as much as 800 to 1,000 feet at Bridge Creek. BULE DERI WOles Za Ire. & GEOL. UNIV. CAL, EROSION Upper JOHN Day, HAYSTACK VALLEY, SHOWING SANDS AND GRAVEL, FORMS NOT PARTICULARLY CHARACTERISTIC OF THIS HORIZON. Fig. I, FIG. 2, MASCALL FORMATION WITH UNCONFORMABLY OVERLYING RATTLESNAKE BEDS. NEAR MOUTH OF RATTLESNAKE CREEK. ie Fas ar MERRIAM. | John Day Basin. 295 At most John Day localities, including Bridge Creek, Turtle Cove, and the entire region of the North Fork, the uppermost beds in the section are buff, tufaceous, or ashy deposits, sometimes with sand and gravels near the top. These beds show a thickness of at least 300 to 400 feet, and perhaps much more in some localities. They are usually harder and are generally exposed as steeper bluffs than the strata of the lower divisions. The steepness of the bluffs is sometimes partly due to the fact that they are protected by the lavas above, but even where there is no protective covering they tend to assume the same erosion forms. In the North Fork region, at Monument and Hamilton, red and pinkish beds, resembling the Lower John Day somewhat in color, are found next to and grading into the uppermost division. It is quite certain that some of these exposures at Monument are really Upper John Day, and a close examination shows the rock to be lithologically different from the typical basal shales. At Hamilton a considerable thickness of red beds, looking at a distance much like the typical lower division, was seen to be apparently immedi- ately below the upper beds. it was not possible to examine the exposures and it is not known whether the middle division is miss- ing here or whether the beds are Upper John Day similar to the red phase at Monument. This division contains the only typical sands and gravels in the John Day and the only known remains of fresh-water mollusca occur here. Excepting a single leaf, the only plant remains known to occur in the series are in the upper division. While it has not been possible for the writer to draw sharp lines between the divisions discussed, the lithologic characters are in general sufficiently well marked so that one is enabled to deter- mine the horizon in the series to which beds in question belong. Paleontologic Classification —That the fauna of the John Day region changed considerably during the period of deposition of this series has already been shown by Wortman,* who has proposed a division of the series on a paleontological basis into lower or Diceratherium beds and upper or Merycochcerus beds. Wortman * Extinct Camelidz of N. America, Bull. Am. Mus., V. Io, p. 120. 206 University of California. [Vor. 2 mentions two species of Merycochwrus, Gomphotherium cameloides, Elotherium humerosum, and Mesohippus prestans, as characteristic of the upper division, while Decerathertum is the typical form of the lower division. Dr. W. D. Matthew has recently shown that the John Day Oreodons referred to Merycochwrus are generically distinct from Leidy’s type. Dr. Matthew has kindly furnished the following note, in which it is shown that these species should be included in a new genus, for which he has proposed the name Paracotylops:— MERYCOCHGRUS Leidy. | PARACOTYLOPS new|EpPOREODON Marsh. | genus. Type, M. proprius | Type P. (Oreodon, Mery-| Type &. occidentalis (Leidy). cocherus) superbus | (Marsh). (Leidy). Premaxille coossified| Premaxille coossified| Premaxille not coossi- along their entire inner| at tips. fied. margins. Nasals much reduced. Nasa/s unreduced. Nasals unreduced. Infraorbital foramen | Infraorbital foramen | Infraorbital foramen above m.!~* above p.‘ m.! above p.° Face suddenly narrowed | “ace more gradually nar- in front of orbits. rowed in front of orbits. Zygomata greatly ex-| Zygomata_ greatly or panded. , moderately expanded. | Mastoid process greatly | Mastoid process of mod- expanded into a broad|_ erate size. transverse plate. Occiput broad and short, | Occiput high and narrow, sagittal and transverse sagittal and transverse crests nearly buried crests very prominent. in cellular tissue. Cellular bony tissue Little or no cellular bony extensively developed! issue on posterior part on posterior part of of skull. skull. | Neck very short. eects rather — short’”’ | (Scott). | Face gradually narrowed in front of orbits. |Zygomata moderately expanded. _Mastoid process not ex- panded. Occiput high and narrow, sagittal and transverse, crests prominent. No cellular bony tissue on posterior part of skull. Neck of moderate length. Owing to the change in the name of the characteristic fossil of the Upper John Day, the writer suggests that this division would more appropriately be denominated the Paracotylops beds. In correspondence regarding the relation of his classification on MEeRRIAM. | John Day Basin. 297 the basis of faunas to that of the writer, Dr. Wortman states that his Paracotylops (Merycochcerus) beds are doubtless the same as the upper division here proposed, and that his Diceratherium beds would correspond to the middle division. This leaves the lower division without a palazontologic designation, until its fauna shall be discovered. Attention is called in this connection to the fact that in most classifications of the continental Tertiary beds of North America this division is .omitted. The collections made by the University of California parties have all been labeled as accurately as possible in the field with reference to horizons, and it is hoped that when the material is finally gotten into form for study it will be possible to obtain more information regarding the vertical distribution of species. Judging from field observations alone, Dr. Wortman would be justified in his classification. The large Paracotylops forms were found to be principally, if not entirely, confined to the upper beds, the Oreodons being principally represented by Zporeodon in the middle division. Remains of the large Elotheres are most abundant in the buff beds, though they are known also from much lower horizons. Remains of Gomphotherium, probably camelotdes, were found only in the upper division, where they are quite abundant near the junction of the North and South Forks. Dv¢ceratherium is certainly more abundant in the middle division, though it probably occurs in the highest beds as well. In a special report on the purely paleontological results of the work of the expedition, this question will receive further consider- ation. Extent and Stratigraphic Relations—The John Day beds are found exposed interruptedly along the John Day River and its tributaries from Clarno’s Ferry up to the Picture Gorge, just below Dayville on the South Fork, and probably as far east as Granite Creek on the Middle and North Fork. North of the mountains unmistakable John Day is seen at Fossil and Lone Rock. Expo- sures near the town of Antelope are possibly also a part of this series. South of the mountains typical deposits are known at Logan Butte near Price. At Bridge Creek and in Turtle Cove the whole section is 2098 University of California. [Vor. 2. exposed. At Clarno’s Ferry the lower and middle beds are well shown, and possibly the upper beds in part. About five miles below the ferry lava beds rest directly upon the middle division. Along the main river from Haystack Valley to the junction of the North and South Forks, and from there along the North Fork to Monument, it is principally the upper beds, occasionally with the middle division, that are found. Onthe Middle Fork the upper beds seem to be the only part of the section present between the pre-Tertiary basement and the lava. At Fossil several hundred feet of the upper division appear between the Clarno and the Columbia lava. At Lone Rock only the Upper John Day is exposed, though the other divisions may also be present. Mr. V. C. Osmont states that south of the moun- tains at Logan Butte there is a great thickness of John Day beds, estimated at between 3,000 and 4,000 feet, composed of the upper and middle divisions, with possibly a portion of the lower one. The bottom of the section is not exposed. Though the exposures are not continuous, Mr. Osmont thinks that the beds are pretty certainly not repeated by faulting. Aside from the exposures at Logan Butte, the writer is not aware of the existence of any out- crops of typical John Day south of the Blue Mountains. The widening of the basin of deposition indicated by greater extent of the upper beds may have been only toward the north, but if the southern section is, as it appears, much thicker than the northern, it is only reasonable to suppose that the basin extended for a considerable distance to the south beyond the farthest point to which it has been traced. The John Day beds are usually slightly disturbed. They are generally tilted five to ten degrees. From the observations made by the writer, no definite system of folds: could be made out, though there seem to be several which trend east and west. Fault- ing is not uncommon and in some places there has been much friction along the fault planes, so that the soft beds have been changed into hard slate bands several inches in thickness. Both the normal and reverse types of faults are represented. Toward the west end of Haystack Valley a break of unknown extent brings what are probably Middle John Day strata up to the level of MERRIAM.] John Day Basin. 299 the highest beds of the series. At another locality, some miles east of this point, numerous thrusts are beautifully shown in cliff sections. Along the North Fork two systems of fractures were noticed. One trends north and south and the other appears to cross it at nearly a right angle. As has already been indicated, the series is evidently uncon- formable upon the Clarno. In the whole of the region occupied by John Day north of the southern range of the Blue Mountains, it is covered by the Colum- bian lavas, being accessible only in the deep canons, where it has been exposed by extensive stream corrasion. At every locality in the basin where the series can be seen, its relations to the overlying formations are beautifully shown. In several places, notably at Sheep Rock in the upper end of Turtle Cove, and on the main river below Spray, residual hills in the middle of the valley are capped by portions of the lower flows, which have served to protect the softer beds beneath. j The Columbia lavas are in some places seen to be decidedly non-conformable to the John Day. Near Haystack the fossil beds form a fairly sharp anticline below lavas which are almost horizon- tal. At Clarno’s Ferry lava flows are seen at one locality to rest upon the middle beds, the typical upper division being absent. At many points where the contacts of Columbia lava and John Day were examined, fossil wood was found to be abundant. In one place at the lower end of Turtle Cove, where there was much petrified wood at the contact, branches of trees were found pushed up into the lava beds. Some of these stems showed an interesting mode of preservation, being unaltered charcoal on the outside, while the interior was petrified. Evidently the John Day had been slightly crumpled, had suf- fered erosion for a considerable period, and was at least partially covered by forest when the first lava floods were poured out. Mode of Deposttion—The John Day beds have generally been considered as entirely of lacustrine origin, and probably a part of the series has been formed in that way. There are, however, cer- tain peculiarities about a considerable portion of the section which it is difficult to explain by this theory. 300 Oniversity of California. [VoL. 2. As has previously been stated, the John Day is largely made up of volcanic ash and tuff, which does not appear to have suffered much from working over. Sands, gravels, and muds, such as belong to characteristic lake beds, are confined to the top of the series. While molluscan remains are quite common at many hori- zons, fresh-water forms are known only in the sands and gravels mentioned above. The numerous molluscan shells, found in the ash and tuff beds, are of land forms. Plant remains, also, which characterize lake beds are, excepting some petrified wood, confined to the highest strata. A solitary leaf, found many years ago in the middle stage at Turtle Cove, is the only known exception to this rule. Fish remains have not been found at all in this series. Tortoise bones are very abundant, but so far the writer has not learned of the existence of any water forms of this order. The only aquatic mammalia which have been found are rodents. Remains belonging to members of the beaver family seem to occur at several horizons through the section. In short, while organic remains are abundant in the greater portion of the John Day, aquatic forms are found only in limited sections of the series. One could account for the absence of water forms by supposing the lake to have been salt or alkaline, though there does not appear to be any definite evidence in support of this view. An objection to the lacustrine hypothesis as applied to the ashy beds is found in the fact that, while the greater part of the deposit is composed of fine material, large, isolated mammalian bones are scattered all through it and over wide areas of the same horizon. Many of these bones are evidently parts of skeletons which were torn apart and scattered about on a land surface before they were finally buried. If they were carried out into a lake it is hard to understand how they could be selected for distribution in deposits from which all other large fragments of detrital material are absent. Occasionally carcasses might be floated out into a lake and finally buried in fine deep-water deposits. In such cases many, if not all, of the bones would be found together. The pres- ence of a considerable portion of the fossil material could not be accounted for in this way. A possible explanation of these occurrences is that a shallow MerRriAM. | John Day Basin. 301 lake on a wide plain might by expansion and contraction, or shift- ing its position, ultimately cover and bury bones which had been resting for a long time on the land. The same thing could be accomplished by flowing water ina basin where cutting had largely ceased, or by accumulation of wind-carried dust or ash. The strongest argument in favor of the lacustrine hypothesis ts found in the character of the bedding of the series. The stratifica- tion is nearly everywhere absolutely regular and the beds are fre- quently very thin. Bedding of this kind could be developed only on a floor free from all irregularities. Such deposits, where they are not shown to have accumulated rapidly, are usually considered as having been formed in water. Recently W. D. Matthew has suggested* that the White River beds, which the John Day resembles in a measure, are in part of eolian origin. Except for the regularity and thinness of the bedding, such an hypothesis as this applied to the question of the origin of the John Day would have much in its favor. The material being largely ash, there would be no difficulty in account- ing for its origin. If the deposits were formed rapidly enough to prevent dissection, absolute regularity of bedding could be main- tained. Here again, however, we meet with a difficulty, as it is hardly probable that a region subjected to frequent ash showers would be inhabited by such numbers of large mammals as would seem to have lived there. If the deposition took place at intervals infrequent enough so that the region could be a desirable place of habitation, it is probable that under ordinary conditions irregulari- ties of the surface would cause noticeable unevenness in the bed- ding. That the accumulation of the John Day beds occupied a long period is brought out by a study of the vertical distribution of the species, which changed considerably during this epoch. The thinness of the bedding in places might be urged as an argument against a purely eolian mode of deposition. The writer is not familiar with any zeolian deposits that have accumu- lated slowly, which show thin and well-marked bedding planes. A theory of fluviatile origin of the series would be open to * Am. Naturalist, May, 1899, Vol. 33, p. 403. w 302 University of California. [Vol. 2. some of the same objections that have been made to the zolian theory. A large part of the John Day seems to have been deposited under conditions somewhat different from any that have been gen- erally recognized as governing the accumulation of extensive forma- tions. Other somewhat similar deposits on this side of the con- tinent appear to have been formed in much the same way. Having originally held to the lacustrine theory of origin for the whole series, it would seem to the writer, after consideration in lights most favorable to this theory of all the evidence obtainable, that, as commonly accepted, it fails to meet fully the necessities of the case for a large part of the section. If it is retained for these beds it will be in some modified form. ‘The writer would suggest that showers of ash, with tuff deposits, on a plain, occupied perhaps in part by shallow lakes, like the so-called lake-beds of the prairie region of the central plains, might form accumulations similar to those in a large part of the series. If the basin were kept close to base level, irregularities of the sur- face would hardly be noticeable. Rapid deposition of ash or tuff would occasionally form homogeneous beds of considerable thick- ness, and would, perhaps, make the region temporarily uninhabit- able for most forms of animal or plant life. During the intervals between such periods of rapid deposition, the surface might be partially covered with vegetation and become the home of such animal forms as have left their remains in the fossil beds. The deposition of small quantities of ash during these periods would not necessarily be a hindrance to the occupation of the region by animals or plants, more than the deposition of loess-like dust in the central plains region has prevented its habitation by a complex fauna and flora. Future investigations may show that some of the very thin-bedded portions of the ash deposits were laid down in water, and that the less distinctly stratified beds are largely A£olian. Fossil Remains.—The mammalian and molluscan faunas of the John Day are already fairly well known from the numerous con- tributions to the paleontology of this region by Marsh, Cope, Scott, Wortman, Stearns, and others, and the objects of this paper do not require a further consideration of this subject. MERRIAM. | John Day Basin. 303 The flora of the John Day was unknown until the summer of 1900, when a small collection of leaves was obtained by the Uni- versity of California party from the upper beds near Lone Rock. These specimens were examined by Professor Knowlton, who reports upon them as follows :— “Three and one-half miles south of Lone Rock [locality 86r ]. Sequoia langsdorfit (Brgt.) Heer. Juglans n. sp. Salix sp. Phyllites n. sp. Fragments. “The locality south of Lone Rock [loc. 861] is represented by a single known species. It is impossible to settle the age from these data, but judging from the affinities of certain of the new forms detected this horizon is possibly not far from that of the Van Horn’s ranch* material. Much larger collections must be made before the age can be satisfactorily determined by the plants.” COLUMBIA LAVA. The name given to the lava formation above the John Day was first used by I. C. Russell}, who applied it to the series of eruptives which forms such a prominent feature of the geology in the area drained by the Columbia River. In the region discussed by Russell there are several distinct horizons of Columbia lava, sepa- rated by important formations belonging to different geological periods. Obviously only one of them can retain the name, if it is to be used as a series or formation name in geological classification. This one should be the horizon which is most prominent along the Columbia River, as it was this formation which suggested the name. In the John Day basin it is found that the lavas of the Columbia form a well-defined series which lies between the John Day and the Mascall formations. Other eruptives in this region are hardly to be confused with it. This series is, moreover, that one of the several to which the name is applied which has the greatest lateral *Mascall formation. { Bull. No. 1o8 U. S. Geol. Survey, p. 20. 304 University of California. [Vov. 2. extent, forming probably the largest lava field of the world and one of the most important formations on this continent. It would seem advisable to restrict the name Columbia lava to this horizon. The lava series is composed of a large number of basalt flows which are sometimes separated by beds of tuff. At Turtle Cove twenty-three flows were counted in the bluff. Nowhere does it seem to be less than 1,000 feet thick, and it would average much above that over the greater part of the basin. Though no attempt was made to trace out any of the flows, it was noted that some of them seem to extend for many miles. A hint as to the mode of exit of the lava is furnished by the occurrence of basaltic dikes in the John Day beds at many locali- ties. The largest and most important of those that have come to the writer's notice are the Davis dikes, which run in nearly a straight line, with few if any breaks, for about fifteen miles through the lower end of Turtle Cove and out into the valley of the main river. The dike shows transverse columnar structure at most points. At the only place where its thickness was estimated, it was about twelve feet in diameter, but it certainly reaches several times that width along a good part of its course. In most places where the contact of dikes with the fossil beds was observed, the bounding walls seem to have suffered little, if any, change. At one point, however, on the west side of Turtle Cove, where the Davis dikes cut the Upper John Day, a most interesting contact phenomenon is noticeable. The ashy fossil beds here exhibit a most remarkable development of columnar structure for a distance of about fifteen feet from the lava on each side. The columns are approximately normal to the surface of the dike and fairly straight. The faces are very even, the columns being as regular and sharply cut as the most perfect structures developed in basalt. The dike at this point is multiple, and por- tions of the fossil beds caught between the leaves have also developed columnar structure, with this exception, that the columns are there much larger than those bounding the dike on the outside. The outer columns are noticeably small, averaging about two inches in diameter, even when ten or more feet in length; while some of those developed in a band of John Day ed MrrriAM.] John Day Basin. 305 deposit about two feet thick, caught in the midst of the dike, show a diameter of about five inches. Evidently the greater heat and slower cooling tended to increase the size of the columns. As far east as the writer’s observations extend, viz., to Dale on the north and Mt. Vernon on the south, the Columbia lava has formerly covered the whole country. There do not appear to have been any islands in this sea of stone. Over most of this region the lava beds still remain fairly flat. They are rarely inclined more than five or ten degrees. Along the north side of the East Fork Valley from Mt. Vernon to Picture Gorge, and from there westerly toward Caleb, the Columbia lavas are inclined sharply to the south. Along the valley they pass beneath the river and below the Mascall formation. At Picture Gorge, where the lavas are cut through by the river, they show a dip of about twenty degrees or more to the south. On the south side of this valley the southern range of the Blue Mountains is capped with Columbia lava. In the Crooked River region the lavas appear again beneath the Mascall formation. Viewing the East Fork Valley from near Caleb it is quite evident that the Columbia lavas are sharply faulted or bent along its south side, the downthrow being to the north. Near the west- ern end of the valley a number of nearly vertical beds are exposed high up on the southern slope. Persons who have visited these outcrops inform me that they are lava, and I have supposed them to be beds dragged down along the plane of a fault or sharp fold. In the depression to the north of the fault plane there rest several post-Columbia lava formations which, as will be shown later, have also been affected by this disturbance. MASCALL FORMATION. Nomenclature-—Along the valley of the East Fork and south of the Blue Mountains, there is found, resting upon the Columbia lava, a series of sediments which have been known in the literature as the Cottonwood * beds, the Loup Fork? beds, the Ticholeptus *Bull. Am. Mus. Nat. Hist., Vol. XII, p. 23, also Jour. Geol., V. IX, p. 72. + Manual of Geology, 4th Ed., J. D. Dana., p. 895. tE. D. Cope, Am. Nat., 1886, V. 20, p. 367. 306 University of California. [Vor. 2, beds (in part), and the Amyzon* beds. Recently Wortman has placed his paleontological horizon, known as the Protolabist beds in this formation. None of these names appear to be applica- ble to the formation considered as a stratigraphic unit. The term Cottonwood is pre-occupied, having been used for a car- boniferous formation by Prof. C. S. Prosser. It is very doubtful whether it can ever be shown that this series and the true Loup Fork occupy the same horizon in the standard geological scale. As yet it has not been done. The Ticholeptus beds probably belong to another horizon than the one with which we are dealing. The correlation of this series with the Amyzon beds was due to its confusion with the Clarno at Bridge Creek. Wortman’s Protolabis beds will doubtless be found to cover a considerable portion of this formation, but as the section is perhaps a thousand feet or more in thickness it is almost probable that it will be found to represent more than one paleontological horizon. It is, moreover, advisable to separate paleontological horizon names from those used for formations or stratigraphic units. It is, therefore, proposed to des- ignate these beds as the Mascall formation. The typical exposure is near the Mascall Ranch, four miles below Dayville. Occurrence and Stratigraphic Relations—In the valley of the East Fork the Mascall formation rests in the depression formed by the deflexed Columbia lavas. (See Fig. 1.) The dip of the lower beds is here approximately the same as that of the lava beds below them; the uppermost strata may be slightly flatter. On Birch Creek and at several other localities, there is some evidence of intercalation of lava flows between the lower strata. The Mascall beds do not reach to the level of the lava plateau to the north, though they may formerly have passed over it. They have suf- fered much erosion and a later formation rests upon their worn edges. So far, the writer has learned of no deposits corresponding to the Mascall in the northern part of the basin. The Ellensburg beds of central Washington, described by Russel,{ are probably *E. D. Cope, Proc. Am. Phil. Soc., 1880, V. I9., p. 61. tJ. L. Wortman, Bull. Am. Mus. Nat. Hist., V. X, pp. 120, 141. t Bull. 108, U. S. Geol. Surv., p. 22., also 20th Ann. Rep., U. S. Geol. Surv., Part II, p. 127. MERRIAM.| John Day Basin. 307 in part of the same age, but may have accumulated in a different basin. At Rattlesnake Creek near Cot- tonwood the Mascall is not less than 800 to 1,000 feet thick. The beds are made up largely of ash and tuff “1 Blyq and are generally light colored, though there are some brownish and reddish strata. Coarse detrital mate- rials are generally absent from the typical section on the north side of the East Fork Valley. Six miles above Dayville there are exposed along the south side of the valley about 400-500 feet of conglom- erate, sand, ash, and tuff, forming a syncline pitching to the southeast. gw The steepest dip seen in the main section here is about 30°, but at the foot of the bluff there are some exposures of gravel beds which are nearly vertical. Pebbles from several horizons in this section were exam- ined, but none seemed to be derived from the Columbia lava. Two other exposures of gravel were seen some niles west of this point, also on the south side of the river. Whether these beds are upper Mascall or whether they belong in some other formation is not clear to the writer. aT[[ANVC pure adios) ainjzdIg UsaMjaq AaeA AVG UYOL Jo yoIexS ‘spaq axeusal}eY Aq paidA0 puv KAT UO SuNseai uoleuUlso} [Bose “BART BIqUIN|OD Ul Nd as105 Fragmentary leaf remains were found about the middle of the section, and sufficient material could possibly be obtained there to throw some light SS \ pt ya yi MN $2 Spsss | upon the age of the horizon. Fossil Remains—The Mascall formation has furnished many fossil remains, including those of mammals, testudinates, fish, and 308 University of California. (VoL. 2. plants. The vertebrate fossils are neither so numerous nor so well preserved as those in the John Day. Teeth and single bones com- prise the greater part of most collections made here. The mamma- lian remains show the fauna to have been of a much more special- ized and higher type than that of the John Day. Fish remains are found associated with plants in the lower part of the formation near the old Van Horn ranch. The single species known from this locality has been referred by Cope* to the genus Plhoplarchus, a member of the perch family. Plant remains are very abundant in the shales at Van Horn ranch and other localities near the bottom of the section. The col- lection made here by Captain Bendire was studied by Professor Lesquereux, who considered it upper Miocene. A collection made by the University party in 1900 was submitted to Prof. F. H. Knowlton, who has furnished the following list, with a statement regarding the probable horizon to which the flora belongs :— “Van Horn’s Ranch, about half way between Cation City and Dayville on East Fork. [Locality 878.] Glyptostrobus ungert Heer. Taxodium distichum miocenum Heer. Idnyites sp. Salix angusta Al. Br. Quercus pseudo-lyrata Lesq. Quercus pseudo-lyrata acutiloba Lesq., Proc. U.S. Nat. Mus., VO). xi; Dp. 17 pl. sa, fie, 1) 1858) Quercus pseudo-lyrata brevifolia Lesq., op. cit. p. 18, pl. x, fig. 2, 1888. Quercus pseudo-lyrata latifolia Lesq., op. cit., p. 18, pl. xii, fig. 1, 1888. Quercus pseudo-lyrata obtustloba \esq., op. cit., p. 18, pl. x, fig. 3, 1888. Quercus n. sp. Quercus 0. sp. Quercus ? sp. Planua ungeri Ett. * Am. Nat., 1889, V. 23, p. 625. MERRIAM.] John Day Pasin. 309 Ficus ? oregoniana Lesq. Laurus n. sp. Aralia whitney? Lesq. Acer bendirei Lesq. Acer dimorphum Lesq: CEVA. Sp: Sapindus obtusifolius Lesq. Prunus n. sp. Prunus n. sp. Hydrangea bendiret (Ward). Marsilea Bendiret Ward, Sketch of Paleobotany, 5th Am. Rept. U. S. Geol. Surv., p. 446, 1883-84. Povana Bendiret (Ward) Lesq., Proc. U.S. Nat. Mus., vol. xi, p. 16, pl. viii, fig. 4, 1888. “Gravel and tuff section, south side of East Fork Valley. Four miles east of Dayville. [Locality 880. ] Carpinus grandis Unger. “The flora of Van Horn ranch [loc. 878] finds its greatest affinity with the Auriferous gravels and allied floras of California and is to be regarded as upper Miocene in age. “The locality four miles east of Dayville [loc. 880] is repre- sented by a single species. A larger collection from this locality will be needed before the age can be satisfactorily determined by the plants.” It is the plant and fish horizon of the lower Mascall which Cope referred to the Amyzon beds. It was apparently supposed to have the same relation to the John Day as the Clarno leaf beds at Bridge Creek. Origin —The numerous remains of plants and fish in the fine white beds at Van Horn Ranch indicate lacustrine conditions at this locality during the early portion of the period. Similar leaf beds in the Crooked River region which have been described to the writer possibly originated in the same way and at or near the same time. In the upper part of the section at Cottonwood, the conditions of deposition, so far as can be ascertained, seem to have been similar to those under which the John Day was laid down. Should 310 University of California. [Vot. 2. the gravels on the south side of the East Fork valley prove to be the uppermost beds of the Mascall formation, the era of deposition would appear to be concluded in a manner similar to that in which the John Day ended. RATTLESNAKE FORMATION. Throughout the length of the Mascall formation exposures in the valley of the East Fork, they are seen everywhere to have been capped at one time by a series of later deposits which have some- times been confused with them. To these beds the name Rattle- snake formation is applied by the writer, the typical occurrence being on Rattlesnake Creek about one mile west of Cottonwood. The Rattlesnake has been referred to by Wortman and Matthew* as the “gravels” at the top of the Cottonwood section. Possibly Cope also refers to them in an indirect way, though the writer is not able to determine certainly just what is meant by his statement. oy} Straugraphy—kIn Fig. 2, Pl. 8, and Fig. 1, p. 307, the typical exposures of the Rattlesnake show it resting unconformably upon the Mascall. It is usually inclined only slightly, having a southerly dip of about five degrees. At one locality on Birch Creek where a section of the Rattlesnake was carefully examined, it was found to comprise 30-40 feet of coarse basal gravels, above this about 25 feet of soft brown tuff, and capping this about 30 feet of rhyolite At other localities more than 100 feet of gravel have been seen upon the rhyolite. The basal gravel beds show a thickness of 200 feet or more in other localities. They are frequently very coarse and contain many pebbles evidently derived from the Columbia lava. In the Birch Creek section the base of the rhyolite flow is filled with angular pebbles of Columbia lava. A stratum about one foot thick at the bottom is largely made up of pebbles, and above that, at least half way up to the top of the flow, pebbles are found scattered through the mass. The rhyolite exhibits everywhere a tendency to split up into large irregular columns about twenty-five feet across. At several localities near the mouth of Beach Creek, a radial or boquet-like columnar structure is beautifully developed *W.D. Matthew, Bull. Am. Mus., V. 12, p. 23. MERRIAM. | John Day Basin. 311 in it. The columns are here about 12-15 inches in diameter. They are sharply separated from each other and show remarkable regularity. The rhyolite extends as a very uniform flow for at least fifty miles westward from Mt. Vernon. It is said by Mr. Osmont to reach up the valley at least 15 miles above Cation City. Osmont also states that it caps the Mascall formation in the Crooked River region. Being much more resistant than the underlying beds, it has tended to form broad tables or terraces wherever it occurs. Fossils—The Rattlesnake gravels contain many vertebrate remains, most of which have heretofore been listed with the Mascall fauna. The Rattlesnake fossils when weathered out are frequently to be found resting upon the Mascall beds below, and as most of the material from both Rattlesnake and Mascall is found detached from the matrix, the difficulties in the way of separating the faunas are considerable. So far no segregated lists of the species have been published. Basin of Deposition—The floor upon which the Rattlesnake was laid down consisted largely of the upturned and eroded Mas- call beds. The basin of deposition was bounded on the north by a range of hills formed by the upper portion of the Columbia lava monocline. At the present time the northern limits of the basin may be clearly seen, as large portions of the deposit have escaped erosion and extend along the northern side of the East Fork valley and westward to the divide some miles beyond Caleb. These considerable remnants all fall into a nearly horizontai plane which abuts against the lava hills to the north. Looking out over the Rattlesnake table-lands from Spanish Gulch one can see an almost continuous series of these deposits, which are in nearly their original position and have not suffered greatly from erosion. It requires no great effort for one to picture to one’s self this part of the basin in its original form. Deformation.—At Picture Gorge, on the north side of the valley, the Rattlesnake rhyolite extends to within a few yards of the Columbia lava and would rest upon it if the section were not interrupted by the gorge. On the south side of the valley it is not well represented, and, where present, is frequently much broken up. 312 University of California. [Vot. 2. The southerly inclination of this bed and its broken character on the south side of the valley indicate that considerable movement has taken place in post-Rattlesnake time along the plane of the fault which has broken the Columbia lava at this point. This movement is a continuation of that which had given the Mascall formation a southerly dip before the Rattlesnake was deposited upon it. , South of the Blue Mountains, according to Osmont, the rhyo- lite flow appears again in its typical form and rests upon the Mascall formation. The present drainage of the John Day must have been estab- lished before the tilting of the Rattlesnake took place, as the river now turns sharply to the north at Picture Gorge, leaving the soft deposits of Mascall and Rattlesnake, which extend farther to the west in the direction which the stream has run for many miles, and cutting straight through the Columbia lava monocline. Had the movement taken place before the cutting of this gap was initiated, the river would probably have been thrown toward the southern side of the valley and would never have come out at this point. Age of the Rattlesnake-—Without making any attempt at exact correlation of the Rattlesnake with any other formation, there seems to be sufficient evidence to show that it should be consid- ered as belonging to the Pliocene of the standard scale; perhaps it represents only the later portion of that period. — Its stratigraphic relations to the Mascall formation are such that it could not be older than early or middle Pliocene, while the amount of erosion which took place between the close of this epoch and the middle or latter part of the Quaternary shows that it could not possibly be later than Pliocene. QUATERNARY. Terraces.—At numerous points along the John Day and its tributaries, one or more terraces are to be found not far above the existing floor of the valley. At the upper end of Haystack Valley on the main John Day, gravels containing numerous large rounded pebbles of rocks not outcropping in that neighborhood are exposed MERRIAM. ] John Day Basin. 313 ona terrace about 75-100 feet above the river. Twenty-five feet below this is the sagebrush flat made up of alluvium with numerous angular boulders and pebbles from the hills near by. At another locality, about two miles farther up the river, water-worn gravels were again seen on well-marked benches. Along a considerable part of the river, terraces representing parts of ancient alluvial fans or slopes are very common. On the north side of Bridge Creek near Allen’s ranch numerous broad, gently-sloping tables separated by gullies sometimes several hun- dred feet deep represent an old and very regular alluvial slope. The stream cuttings here show in places a considerable thickness of the John Day beds capped by irregularly stratified wash from the adjacent lava bluffs. In terrace deposits remains of A/ephas and Eguus have been found at several localities. Near Mt. Vernon, on the East Fork, a nearly complete skeleton of E/ephas primigenins was discovered in an alluvial deposit not much above the level of the river. Whether or not the other remains have been worked over from older depos- its, this skeleton has evidently not been disturbed. Catton Cutting-——The discovery of typical Quaternary forms in deposits so near the valley floor shows that the cafion cutting had been practically finished for some time when Quaternary mammals were still in this region. In other words, the period of active cafion-cutting did not extend to the close of the Qua- ternary. The backward extension of this period is limited by the Rattlesnake. Though the drainage was probably established before the close of that epoch, the great work of corrasion was accomplished after the river began cutting into the uppermost Rattlesnake beds. A palzontological determination of the age of the Rattlesnake would very materially aid in fixing more exactly the probable earlier limit of the era of cafion-cutting. The greatest probable extension of this epoch is from late Pliocene to middle Quaternary. On these broad lines a correla- tion of this period with the Sierran* epoch of Le Conte would seem to be justified. *Jour. Geol., 1899, V.7, p. 525- 314 University of California. [Vot. 2. Ash Beds.—At many localities, particularly in the northern part of the John Day basin, an ash bed of comparatively recent origin is seen in the flood plain deposits or on the alluvial slopes near the streams. In the upper end of Haystack Valley a stratum about 1% feet thick is exposed at several places in the river bank. It is here covered by 6-10 feet of alluvium with angular pebbles. On Rudio Creek there are fine exposures of an ash bed along the bank of the stream. The bed is here much thicker than at Haystack. Similar deposits were seen as far east as the writer has explored. Though deposits somewhat similar to those described might be formed by material washed down from fossil beds or other deposits of volcanic materials, the origin of these beds can not be ascribed to such a cause. Where they have been carefully - examined the ash is perfectly pure and is sharply separated from the deposits above and below. It has apparently not been worked over appreciably and was probably deposited rapidly, otherwise it would be mingled with other detrital material. Its deposition is evidently to be correlated with some catastrophic volcanic outburst occurring in comparatively recent times. Possibly it has been de- rived from the volcanoes of the Cascade Range. University of California, April, rgor. v i ri . a waN, UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology Vol. 2, No. 10, pp. 315-326, PI. 9. ANDREW C. LAWSON, Editor Mineralogical Notes BY e ARTHUR S. EAKLE With Chemical Analyses, by W. T. Schaller Pat F ux wig PX. *,. Gy SSS AD he NIZED a *Peeeeveneeue® %, i? %o, BERKELEY PUBLISHED BY THE UNIVERSITY NOVEMBER, 1901. PRICE, 10 CENTS \ UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology Vol. 2, No. 10, pp. 315-326, PI. 9. ANDREW C. LAWSON, Editor MINERALOGICAL NOTES. BY ARTHUR S. EAKLE. WITH CHEMICAL ANALYSES, BY W.T. SCHALLER. CONTENTS. PAGE. I. Pectolite, Datolite, and Other Minerals occurring near Fort Point, Sanshinan CisGoOs Galles v2. secseen sense ects svcussecacas ovespanecesesasGess esl edons six 315 IRE CLONE Neeser mec heec cacatnle mugen otivs Wa scioiuiv decide Ree Peudum cacicdeaneeteecteness 316 Wat lite gies eescse esses. cco sands cogeec seen weniecdeveaweceessercacelsatecbecade 317 II. Zircon Crystals from Siskiyou County, California...........-ssceeseeeeeeee ees 319 Ill. Esmeraldaite, a New Hydrous Sesquioxide of Iron, from Esmeralda County Nevada ees. cis ccc. cesdisvess cedanetedssccsncsees sovssvsescascen ss seugtaates 320 IV. Coquimbite, from the Redington Mine, Knoxville, Cal..................5 322 V. Altaite Crystals, from Sawmill Flat, Tuolumne County, Cal.............. 324 I. PECTOLITE, DATOLITE, AND OTHER MINERALS OCCURRING NEAR FORT POINT, SAN FRANCISCO. THE coast rock on the southern shore of the Golden Gate, extending for some distance on both sides of Fort Point, consists of serpentine, which represents the northern outcrop of the great serpentine laccolith, extending across the city of San Francisco, intrusive in the Franciscan sandstones. This mass of serpentine has been described by Palache,* and classified by him as a lherzo- lite-serpentine. Numerous boulders of serpentine are strewn along the beach west of the fort, which show manifold varietal differences in color and structure, and contain abundant veins of secondary *““The Lherzolite-serpentine and Associated Rocks of the Potrero, San Francisco,”’ this Bulletin, 1894, Vol. 1, pp. 161-192. 310 University of California. [Vot. 2. minerals, thus offering a very interesting field for mineralogical study. The main mass of serpentine is dark green, with often a mottled appearance, due to numerous phenocrysts of original ensta- tite, which show shining bronze-colored cleavage faces. Narrow veins of very compact light green serpentine traverse the dark green boulders, and these are generally accompanied by thread-like veins of finely-fibrous chrysotile, which form a border on each side of the light green. Among the secondary minerals, forming the white veins, which so abundantly seam the serpentine, magnesite appears the most common. It is snow white and very compact and hard usually, but where the mass of serpentine is much decomposed, the mineral occurs in small botryoidal forms, and is softer, owing, probably, to an alteration in part to hydromagnesite. Calcite is also abundant, mostly in cleavage masses, sometimes in small scalenohedra. Long and slender colorless prisms of aragonite, white tabular crystals of barite and small gypsum needles are also occasionally found in the fissures. Grayish-brown opal occurs in small rounded inclusions in the serpentine on the east side of the fort. A few hundred yards west of the fort a large mass of rock outcrops on the shore of a different nature from the serpentine, and is probably a remnant of an older basic rock included in the serpen- tine. The mass has a foliated or somewhat schistose structure due to shearing, and is highly altered to chlorite, and contains the veins of pectolite and datolite. FPectolite—The numerous pectolite veins are generally very nar- row, sometimes mere white threads, but occasionally they widen out to several inches, the one from. which most of the specimens were collected being about four inches in width. The mineral is fibrous and generally very compact and tough, with a more or less radiated structure. In some parts of the vein the fibers are coarser and not so densely compacted. On one specimen short and rather broad prismatic crystals, considerably rounded by wave action, occur. They apparently consist of a broad base c(oo1), a broad orthopina- coid a(100), and two prisms, perhaps (540) and (140),as indicated by measurements with the contact goniometer. The color of the mineral is snow white, but much of it is stained reddish by varying amounts of ferric oxide. _— — = EAKLE.] Mineralogical Notes. 31 a A mean of two analyses of the whitest mineral is:— SIO gar get mes 53.40 Al,Os | BOuie ec: 3187 CAO Wan tress se 30.56 Na ata ee ones s 7.61 HO} ienitions.... =... 4.46 99.99 Datolite—Veins of datolite are about as numerous as those of pectolite in the rock and the two minerals frequently occur together in the same fissure. Many small druses of clear, colorless datolite crystals occur, and these furnished the best crystals for measure- ments. One vein about six inches wide is composed of calcite, pure white kaolin and datolite, intimately mixed, and some of the datolite crystals in this vein reach a dimension of a_ half cen- timeter in length and width. The orientation for datolite, chosen by Dana in his ‘“‘System of Mineralogy,’* instead of the one commonly adopted by the German mineralogists, is the most natural one for these crystals, and is, therefore, adopted here in the accompanying figures, using his axial ratio also. Owing to the characteristic wavy and striated faces on the crystals, the measured angles with the reflecting goniometer varied considerably, but they served for the complete identification of the forms, a total of nineteen being observed, as follows. — c(oo1) 4(102) A113) a(100) u(104) H(114) m(110) &(102) 116) o( 120) n(111) g(312) Mort) W(T11) A(121) g(012) €(112) 7(231) (Teton? ”) *E.S. Dana, ‘‘System of Mineralogy,’’ 1890, p. 502. 2 318 University of California. [VoL. 2. m(110) is the predominating form and is represented usually by broad wavy faces. c(OO1) is common, with generally small faces which are charac- teristically striated parallel to the positive pyramidal edges. a(100) is not very common, and the faces are generally narrow. n(1i1) and &112) are the common pyramidal forms and are always well developed. M(o11r) is always present and the faces are long and narrow. g(ol2) occurs on but few of the crystals, and then as very narrow faces. This is the unit prism of the German mineralogists. 4(102) rarely occurs, and the faces are always dull or etched. (1. 1.18)? This form was observed on two crystals, as narrow faces. Angles measured. Calculated for symbol. (OOT) Gr i1S m7 at. fie es vis pa The base on both crystals was striated and the readings were consequently not perfect enough to place the symbol for the form out of doubt, since the form makes such a small angle with the base. The remainder of the forms observed are represented by quite narrow faces, and are of rarer occurrence on the crystals, a large majority of the crystals having the combination 77(110), c(oo1), n(111), &(112), and A@(o11). Figure 1, Pl. 9, shows this combination and also the general habit of the crystals. A rarer type is tabular parallel to the base and has a compara- tively broad face of a(100) in addition to the other forms. This is seen in Figure 2, Pl. 9. Figure 3, Pl. 9, represents a type that is more elongated in the vertical direction, and with some of the narrower forms present. Figure 4, Pl. yg, shows a more complete combination of forms with the common habit. EAKLE.] Mineralogical Notes. 319 An analysis of the mineral showed the composition:— Per cent. SiQ pine as freetb stone e071 AO press cise Onl CAOE i cntetneetan ts Bc.03 IB Oars saaveiecne ene < DOA HO ignition... 6.52 99-34 The mineral was dissolved in hydrochloric acid, and then evaporated several times to dryness, on the water bath, with the addition of methylalcohol to expel the boron, and the silica and bases were then determined. The boric acid was determined by distillation with nitric acid, and methylalcohol and the distillate then titrated. All the water was expelled at a low red heat. II. ZIRCON CRYSTALS FROM SISKIYOU COUNTY, CALIFORNIA. Several small zircon crystals obtained from the panning of gold bearing black sands, about forty miles from Fort Jones, Siskiyou Co., Cal., were sent to the writer by Dr. C. S. Cowan, for identifi- cation. The crystals are transparent, and vary from very pale to deep wine in color, resembling quite strongly wine-colored topaz crystals in general appearance. They range from two to five milli- meters in size and are about as long as they are broad. The faces are exceptionally bright and perfect, and yield the most perfect reflections. The forms observed are:— a(100) e(1O1) (110) P11) ale) 2(511) The measurements made with the reflecting goniometer were as follows:— Measured. Calculated. @ : £=(100) : (311) Bu, e413" Sn @-2=(100)): (511) 200021" 20° 25 320 University of California. [Vot. 2. Measured. Calculated. 2 P= Moo)) Ti) 61° 40’ 61° 40! 2 €—(100))- (om) ypaee 24 ype aid! @ :m=(100) : (110) 45° 0! AG Ou Wt: pP=(T1O): (117) 47> 50! AT a5 Ol = (ETO) sai) 86. Ar 3074 is € =( TIO) (tom) 63° 36! 633354 p :#=(11T) : (311) 29° 57’ 29° 57’ p> él De (101) 28° 20° 28-201 ¢: e€=(101): (011) 44° 50! 44° 50! x: p=(311) : (110) 53° 109! 53° To! He e= (301) s (501) 11° 18! 11? 22! The crystals are remarkable for the large development of the ditetragonal pyramid 2+(311). It is present on all of the crystals, with the faces nearly equal in size those of a(100) and e(1or), these three forms predominating. The general habit and relative size of the forms on the crystals are shown in Figure 5, Pl. 9. A few of the crystals are water-worn, but the majority have their edges very little roughened or their faces marred. The nearly colorless ones are evidently bleached out, as very little heating of the deep wine crystals produces perfectly clear colorless ones. The original source of the crystals is unknown to the writer, but, judging from the very slight abrasion they have undergone, they have not been transported a great distance. Ill. ESMERALDAITE, A NEW HYDROUS SESQUIOXIDE OF IRON FROM ESMERALDA COUNTY, NEVADA. Specimens of yellowish-brown earthy material containing small pod-shaped masses of a coal black mineral were sent to the depart- ment, some years ago, by Mr. W. H. Shockley, from Esmeralda County, Nevada, and analyses have lately been made of the material by Mr. Schaller. The brown earthy mass is apparently a highly siliceous limonite containing about 14% Fe,O,. The black mineral proves to be a ferric oxide with a high percentage of water and with considerable impurities, notably of phosphorus and aluminum. It has been deposited in the cavities of the earthy mass in a solid amorphous EAKLE.] Mineralogical Notes. B21 form very similar to opal deposits. The mineral has a coal black color and a bright vitreous luster, showing an occasional iridescent tarnish. It is translucent on its edges, and thin splinters are yellowish-red in transmitted light. The minera.,is exceedingly brittle, and breaks with a conchoidal fracture. It has a hardness of 2.5 anda yellowish-brown streak. It is easily and completely soluble in acids, but infusible, becoming magnetic after ignition. The average of several analyses of the black mineral showed the composition :— Per cent, en OL eh Uc AO ea ye ee eae 56.14 NAO ee eee oa tohrectr ee Aavce culate hays Gries ered CAO sc. ene ons eats Euniastens bak oiere aneeptegee 2.35 gs ©) Prep ecu tec tee eeu ctmeeet cusucy s Enea shay Nearer rte ener 4.49 OGROOMIC tipi fot hoes Patan ae oa aothuns a7 LORY oon ate res sn Wane pane gasaiey sou whales 2.05 H1@rat rio’ Clas Pies toh caey Soha Song anes ane 15.94 EE @eOVer WOw CRewr cers creceyecesboes cia cones ee 10.2 99-35 The specific gravity is 2.578. When the mineral was heated over a blast lamp, the ferric oxide became somewhat reduced, owing probably to the presence of some organic matter. As the amount of water obtained by direct weighing was 26.187, and by ignition at low red heat with- out any apparent reduction was 27.55 //, the difference, 1.37//, prob- ably represents this organic matter. The water expelled at 110° C. was readily reabsorbed by the pulverized mineral, and since the mineral is a solid homogeneous body, all the water driven off may well be considered as belonging to the composition of the mineral. It is impossible to state in just what condition the phosphorus and other oxides exist in the substance, so, if we reckon them as impurities and consider the mineral as a simple hydrous sesqui- oxide of iron, the analysis reduced to 1007 becomes :— Per cent. Ratio. Ton aan) sete iia a.tencais 68.20 A6T 1 Tal) Ry uneie ten. oe omens ase 31.80 17.66 4.14 322 University of California. [Vo. 2, This gives a ratio of ferric oxide to water of approximately 1:4, corresponding to the formula Fe,O, 4H20O. The mineral resembles limonite in the nature of its impurities and color of its powder, but differs from it radically in the amount of water, low specific gravity, hardness, and its clearly amorphous, glassy nature. The analysis approaches more closely to those of limnite. It is the same kind of deposit and probably resembles in appearance melanosiderite, described by J. P. Cooke,* but there is no question about the mineral being an oxide. The mineral has such distinctive characteristics that the name esmeraldaite is proposed, to distinguish it from the other hydrous ferric oxides. Portions of the deposits, while still retaining the structure and general characteristics of the black mineral, have by some change lost the bright vitreous luster and become dull and dark brown in color. A partial analysis of this brown variety gave Fe,O,; 50.26/ and H,O 22.70/. This shows the relative proportion of ferric oxide to water to be about the same as in the black mineral; but a greater amount of impurities is indicated. IV. COQUIMBITE, FROM THE REDINGTON MINE, KNOXVILLE, CAL. A green ferric sulphate, which was found in the Redington mercury mine in a wet, mushy condition, became quite compact and crystalline after a natural drying for several months in the air, and the compact material has been recently analyzed by Mr. Schaller. The color of the sulphate is light yellowish-green with patches of dark green, and the structure is distinctly fine granular. Under the microscope the mass is seen to consist of minute, doubly- refracting plates and grains which resemble rhombohedral plates in form, but the small size of the individual grains prevented any definite conclusions regarding the crystal system. An attempt to recrystallize the mineral produced only a highly deliquescent salt. In its various properties the mineral is similar to coquimbite. The hardness of the more compact portion is about 2-2.5. The *J, P. Cooke, Trans. Amer. Acad. Arts and Sciences, 1875, 10, 451. EAKLE.] Mineralogical Notes. 223 taste is strongly astringent and the water obtained in a closed tube is strongly acid. The mineral is soluble in water, and when the solution is heated, a precipitate of red sesquioxide of iron is formed. It is easily and completely soluble in dilute acids. Two analyses of the mineral gave as its composition :— Mean analysis Per cent. Per cent. Per cent. Ratio. FeO; 12.95 13.03 12.99 Hoh Al,O; 7-30 7:58 7-44 729 SO; 38.44 37-63 38.04 4-755 EO at 110°.) )23/32 24.13 2272 13-179 | 20.796 H,O, ignition 13.40 14.02 a7 TiO, oe FeO 0.13 0.14 0.13 SiO, 0.17 0.24 0.21 Na,O 1.68 1.68 1.68 MgO 1.09 1.14 1.09 98.48 99.59 99.04 The analyses show that the mineral is essentially a hydrous sulphate of iron and aluminum, the other oxides present being simply impurities. In calculating a formula for the mineral, the only difficulty that arises is with respect to the amount of water which really forms a part of the mineral’s composition. It is highly probable, from the fact that the material has been gradually drying out, that the water expelled at 110° C. was partly that of crystallization and partly occluded. The ratio obtained from the mean analysis corresponds very nearly to the formula Fe,SO,); Al,(SO,); 27H,O. Assuming all the H,O present as water of crystallization, then our substance might be viewed as a mixture of the two minerals, coquimbite, Fe,(SO,); +9H,O, and alunogen, Al,(SO,),+18H,O. Such a mixture would require the following percentages of the oxides:— Mean analysis reduced to 100%. FeO; 13.03 13.54 ALLO; 8.30 7.70 SO; 39.10 30.67 H,O 39-57 39-03 100 100 324 University of California. [VoL. 2. The calculated percentages for the mixture agree fairly well with the reduced analysis, but there is nothing to indicate that the substance is other than homogeneous, In view of this fact and the high probability of occluded water in the analyses, the writer is inclined to the belief that the mineral is wholly coquimbite, since it possesses properties so similar. In this case, about one-half of the iron has been replaced by aluminum, and about Io per cent of the water must be regarded as occluded. The analysis, calculated as a pure ferric sulphate containing only the amount of water necessary for coquimbite, becomes:— Required for coquimbite Fe,(SO,);+9H,O FeO; 27.99 28.47 SO; 43.18 42.70 leh) 28.83 28.83 100 100 | The mineral constitutes an additional member of an undoubted series of sulphates, and mixtures of sulphates, in the Redington Mine, resulting from the decomposition of the abundant marcasite. Melville and Lindgren* have reported the occurrence of copia- pite, Knoxvillite, and Redingtonite from this mine, the analyses of which minerals differ quite materially from the coquimbite, no chromium being found in the coquimbite. V. ALTAITE CRYSTALS, FROM SAWMILL FLAT, TUOLUMNE COUNTY, CALIFORNIA. Some delicate little specimens of gold, cementing minute, dark gray isometric crystals, came from a pocket in the Birney pocket mine, near Sawmill Flat, Tuolumne County, Cal., and an analysis of these crystals by Mr. W. J. Sharwood, to whom the writer is indebted for these notes, shows them to be altaite crystals. The gold and altaite are intimately associated, some of the crystals having a gold coating, while the majority are perched on the ends of gold stems or wires. The crystals are from 1-2 mm. in diameter, and are mainly *Melville and Lindgren, Mineralogy of the Pacific Coast, 1890, Bull. 61, U. S. Geological Survey. EAKLE.] Mineralogical Notes. 325 combinations of the octahedron and cube, the former predom- inating. Many of them, however, have the cubo-octahedral edges beveled by narrow faces which measurements show is the trapezohedron, (322). The measurements with the reflecting goniometer were:— Measured. Calculated. (111) (CLry) Toca 70° 32" Cue een) 109° 24’ 109° 28’ Giant \e(ee2 NA eds i 2 The typical appearance of these crystals is illustrated in Figure 6, Pl. 9. The analysis shows the composition of the crystals to be as follows:— Calculated for Pb Te. Per cent. Per cent. Te 32.5 37-7 Pb 65 62.3 (ioe ar liraces up to On An None Fe Trace Se ss S 4c In one portion gold to the amount of 6 per cent was found, but this was doubtless due to a mechanical admixture of the intimately- associated gold, as the purer material gave no test for gold. The analysis differs somewhat from the theoretical composition of altaite, yet it is sufficiently near to indicate that the crystals are altaite. Some of the gold is in the form of highly-distorted octa- hedrons, and partial analyses of these crystals gave 91.2 per cent to 94.2 per cent gold. Crystals of altaite are exceedingly rare in occurrence, and only the cube form has heretofore been observed. Massive altaite showing cubic cleavage occurs at the Stanislaus Mine, Calaveras County, and has also been reported from the Golden Rule Mine, Tuolumne County, by Genth.* University of California, October, Tg0L. *F, A. Genth, Amer. Jour. Science, 1868, 45, 312. UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology 327-348, ANDREW C. LAWSON, Editor CONTRIBUTIONS TO THE ae ey [ yes _ TIINERALOGY OF CALIFORNIA Aa BY WALTER C. BLASDALE e ‘ ' ghee cent * OF ¢ '4>* SHAT’ L oe oN, Ny Yj Yf “i oO YY 7 ly \ Ce WP Z ys, en => ay, My V % NI \\ ay 4 UI A ; _ BERKELEY -PUBLISHED BY THE UNIVERSITY i NOVEMBER, 1901. PRICE, 15 CENTS = UNIVERSITY OF CALIFORNIA Bulletin of the Department of Geology Vol. 2, No. 11, pp. 327-348, ANDREW C. LAWSON, Editor CONTRIBUTION TO THE. MINERALOGY OF “CAT TFORNTA, Se WALTER C. BLASDALE. CONTENTS MMtrOGUCTION:.../...0.c0+0s Sec ehact Chane Reeenetesuave sachasieenes woes ales tpacteenecsarece paw nesee 327 PAMIG LECTIMELOMMb lem Ges sce-cca.cnsces sicdsaccaceioeeseecsssaceeacseccucsetees cessecssecvedsssusees 328 @CCunnen Cen cesseetca ce cecemaast ee ce cueaen cies iecenscenssnaceMecstaresiane semssacacscnsres? 328 GeneralMl) CSGriptiOnl ivccvsces.ssechadescaee sieceeedcseesesciisasancwsnes cosoeseeessere: esse 329 OHticalkRropertleswecesucssaducseccdemer stcclieaersteciscseeseceitesrtewaneenicccenreeciseseeses: 329 (Wohestonal PrOPEctleSii::..csecciccse see jecce se rcelaswcccseccsoecacecsctaeeuetstiescvecceses 330 ChremicalUP ro pentiesMe nec coodeccsctave see ve ores cas scdrssrcepometsanestaeecnecceneres 332 MMB ues orn blen devir.teccvestessessivscctsasssoesesssnseancests isenescesilesdoseves vecwsesen ctl sy 335 @ CCUKENC Ctizeesencoseeroncseses clicce csceey curenstearsoasuecsitestalerisse eres bues teres esti scee 335 Generale cScrlp tomers: neccsvc$>2. Sections parallel to the ver- tical zone sometimes show unequal absorption. A similar phe- nomenon was noted by Palachef in crossite, and by Dalyt in philipstadite. Cohesional Properties —The study of the cohesional properties of minerals has been applied to the members of the hornblende series with marked success by Daly.|| The material under consid- eration yielded only prismatic planes, which were of sufficient dimensions to admit of a satisfactory application of this method. Also the microscopic cracks previously noted rendered it difficult to obtain crystals which did not give rise to abnormal results, since solvent action took place along these planes with great rapidity. The crystals, or cleavage flakes, were etched with strong hydro- fluoric acid at the temperature of boiling water for periods varying from one to five minutes. Examination of the pits thus produced was made with transmitted light, using a magnification of about two hundred diameters. Essentially the same results were obtained from crystals as from cleavage flakes, and no differences were observed in the behavior of the actinolite from the two localities. * Comptes Rendu, Tome 106, p. 777. + This Bulletin, vol. 1, p. 190. t Proc. Am. Acad. Arts and Sciences, vol. 34, p. 434- || Proc. Am. Acad. Arts and Sciences, vol. 34, p. 374. BLASDALE.] Contribution to Mineralogy. 331 The general features of the etch-pits thus obtained are shown in the accompanying figures. No. I represents a partly- and No. 2 a fully-developed pit, No. 3 represents a group of pits one of which has attained its perfected form. The essential character of all the normally-developed pits consists of three curved faces, Cc Fig. 1. Fig. 2 Fig. 4. which form a solid angle near the center of the pit, and intersect the crystal plane in three lines, two of the latter being straight or very nearly so, and of nearly equal length, the third forming a long bow-shaped curve. One of the straight lines forms a slight angle with the prismatic cleavage trace; the other, commonly the longer, is at a considerable angle with it. In general the figures closely resemble those obtained with normal actinolite by Daly, the variations, such as are observed in the curvature of the longest line of the figure, being no greater than those obtained in etching different crystals from the same locality. For the angle between the line AB and the cleavage trace Daly obtained values varying from —2° to +12° according to the stage of development of the figure; the present material gave members ranging from 4° to 8° 15’; for the angle between AC and the cleavage trace Daly obtained from 10° to 16°, while the material under consideration gave from 10° to 16° 36’. The absence of terminal planes in actinolite crystals renders it impossible to correlate with certainty the position assumed by the etch-figures with reference to the crystallographic orientation. A study of the positions assumed by the figures on the four prismatic planes gave results in accord with the orientation adopted by Daly. 32 University of California. [Vor. 2. Os Figure 4 shows the apparent positions, as viewed under the micro- scope, of the figures on the four faces of a crystal, the greater of the prismatic angles lying between A:B and C:D. It is to be noted that the most acute angle of the figure points either up or down according to whether the face is to the front or back (normal orientation) of the crystal. In this respect the figures agree with Daly’s statement that the claw” of the figure points towards the positive hemipyramids. Daly deduces the latter statement from an analogy between the etch-figures of actinolite and those of other varieties of hornblendes of known orientation, and Wright* deduces the same relation from a study of a hornblende from Vesuvius. Accepting the above as the correct correlation, the true orientation of the four planes would be as follows: A=(110), B=(tro), C=(110), D=(1to). It is to be noted, however, that these results do not represent the actual position of the figures on the crystal, since in my own figures, and presumably in those of Daly and Wright, no account is taken of the fact that right and left are interchanged. Chemical Properties.—The mineral is scarcely affected by strong hydrochloric acid and was only partially decomposed by heating in a sealed tube with boiling sulphuric acid. Analyses of two carefully-selected and inclusion-free samples are given in Table I. Sample No. 1 was obtained from the boulder that furnished the material used in the determination of the optical properties; No. 2, from a boulder collected at locality B. The two analyses show in their general features no marked variations, the differences being such as might easily arise from the substitution of isomorphous bases. Compared with typical actinolite from Zillerthal (see analysis No. 3) and with other analyses of glassy actinolite (see analyses 4, 5, and 6) there is still a general agreement, the note- worthy differences being the lower percentage of magnesia, and the presence of considerable amounts of alumina, of the alkalies, and of combined water. The low percentage of magnesia is largely com- pensated for by the higher content of ferrous oxide and lime. The alumina appears to be higher than in any of the analyses of this * Tschermak’s Min. u. Pet. Mitth. Band to, S. 317. BLASDALE.] Contribution to Mineralogy. 333 TABLE No. I. Analyses of Green Hornblendes. I | 2 3 | 4 5 | 6 ae : SS eS Sil@ peccssscecesesstone 55.21 55-56 55-50 55-00 55.01 | 56.33 ANS Ogiasvessessssacasas | 3.45 OO San eeecacceere [51 1.69 1.67 Hes Oijnsesteveessm rare) Medes see | sitetenee |. sOhecenes 99 SO 3] Wueeccetens, GUO iis sencsiaisecesen 7.49 | 5 97 | 6.25 3-46 | 3-46 | 4.30 IMPSOG teeneccsnneenen 18.97 19.45 22.56 23,31 23.85 24.00 GajOursicorsteon teens 10.50 12.13 13.46 10.38 13.60 10.67 Nag Os acecosccne ese as 2.45 Sify. fc stadataee | I.I0 | BSG Noeezeess TRO srtest conc cchecere||| woes acts: Se A) wecdecreee Pari 2 oe eter ibeeaccanee FApeOFAteT OOS cageesasi|t masedseaceeh| | Medeaaeess | Brcisess? ||P ee rsestevaphl bctaracers Wp Weeeeaeeen H, O above 100°... 175 2.58 I.29 2.90 1.02 1.03 NIT © rete cae cesestece || asenstedaes ulllnceese oes eee ee hie || 45 teeeeeees 99-82 99:98 | 99-06 | 100.08 | 100.56 | 98.00 1. Actinolite from Berkeley, California. 2. Actinolite from San Pablo, California. 3. Actinolite from Zillerthal, Rammelsberg, Mineral Chemie, S. 471. 4. Actinolite from Scotland, Heddle, Trans. Roy. Soc. Edinburgh, vol. 28, p. 508. 5. ‘Hornblende”’ from Russia, Michaelson, Journ. ftir Prakt. Chemie, Band Ol,.o. 220. 6. Actinolite from Concord, Mass., Seybert, Am. Journ. Science, vol. 6, p. 333. TABLE, Now il: | Elementary | Atomic | Atomic F | Jleme y homic Atomic | . Analysis 1, compen. ouetlant hatio. | Analysis? | Composition. | Quotient. | Ratio | | | SiO, 55-21/Si 25.96} .g2I1 | 25.00 \si Oy, 55-56|Si 26.12 .9270 | 25.00 Al, O; .3.45/Al 1.83] .0680| 1.84 ||Al,O3 2.05/Al 1.09) .o4o4 1.09 FeO 7.49/Fe 5.83) .1048 2.84 ||FeO 5.97/Fe 4.64) .0835| 2.25 CoO 1o9.50/Ca_ 7.50] .1886 5.12 ||\CoO 12.13/Ca 8.67) .2180 | 5.88 MgO 18.97/Mg 11.43] .4744| 12.87 ||MgO19.45|Mg 11.72; .4863| 13.11 Na,O 2.45.Na_ 1.82} .0795 2.16 ||Na, O 1.94/Na_ 1.44] .0629 | 1.70 KelORMe as eeremnenee st lgeeeete so clitettsse-.< K5.O) a3clK 25) .0064 02 Fs Ore. 175d 720\0 20 5-43 ||H,0 2.58)/H 29 .29 7.80 Seueteser ten sensed O 45.26) 2.85 77230 pptaersisiess O 45.76 2.88 77.66 mineral thus far reported, though it does not greatly exceed the total sesquioxide content reported in analysis No. 4. The presence of alkalies, in amounts sufficient to be considered as important 334 University of California. [Vor. 2. constituents of actinolite, seems to be abnormal, but as a matter of fact many of the more recent and carefully executed analyses show that these bases are commonly present. A similar remark might be made with reference to the water content. That the water here reported is constitutional can not be questioned since hygroscopic water was determined by drying at 100° and the material experi- enced no appreciable loss between 100° and 350°. In Table II are tabulated the results of the calculations leading to the determination of the formula of the mineral. It will be noted at once that the oxygen is but slightly in excess of that corresponding to a metasilicate ratio. Most of the theories for the constitution of the hornblende group ignore entirely the presence of constitutional water, which fact probably rests ultimately upon the decision of Rammelsberg* that this is only to be regarded as the beginning of an alteration. In the present material, and apparently the same remark would apply to all of the other analyses of actinolite reported in Table I, no indications of such alteration could be detected. The fact that water is reported in many other members of the group, and that it has been admitted as an important constituent of the closely-related pyroxene pectolite, would seem to demand that it should be included in any structural theory ef the group. Further difficulties in applying the structural theories of Rammels- berg and Tschermak appear with reference to the sesquioxides and alkalies. According to Tschermak’s theory of the horn- blende group, the alkalies must be accompanied by equivalent amounts of sesquioxides, hence any attempt to explain the struc- ture of the present mineral as a mixture of the glaucophane molecule and the actinolite molecule would fail, since the alkali content in both analyses exceeds the sesquioxide content. The theory proposed by Clarke} might be applied with a greater degree of success since it admits the equivalence of K, Na, H, AlO, Fe’’’O. Representing this group of symbols by R’, the dyad gsroup by R’’, and by X a mixture of Si,0, and SiO, in nearly equivalent proportions, the first analysis may be summed up as : Poggendorfi’s Annalen, Band 103, S. 435. ¢ Bull. 125 U. S. Geol. Survey, p. 94. BLASDALE. ] Contribution to Mineralogy. 335 Rt Nis, Res, and the second as Rog, Xyis) Kise. Dhe composition of the two samples may then be represented thus:— I II A Lies P - 6 Re Xe Re ie Rex 1 =R// 99-84 Xie-s0 R%g-44 ee RX, at =R/y1-24 Xi3-10 R/ 10-60 Finally it may be stated that in crystallization, in optical and in other physical properties, the mineral presents no remarkable features, and its differences of chemical composition are not sufficient to warrant separation from the mineral actinolite. A BLUE HORNBLENDE. Hornblendes of a deep blue color are not uncommon in the rocks of the Coast Ranges. One of these was considered by Lacroix* and later by Becker} to be normal glaucophane; a second, the only one fully described up to the present time, was shown by Palache to be identical with a species from Custer County, Colorado, and was named by him crossite. The material used by Palache was obtained from a locality but a few miles to the north of Berkeley, about midway between the two localities here considered, but, as the sequel shows, differs from the mineral here described. Occurrence.—Unlike the actinolite, the blue hornblende is found in rock masses of considerable extent, which must be regarded as one of the important rock formations of this range of hills. Good exposures are not plentiful, but their extent and the variety of facies they present is evinced by the abundance of float strewn over certain areas of the hill slopes. This material often assumes the form of boulders, not dissimilar to those of the actinolite, but commonly consists of more or less angular masses, most of which show a schistose structure. Many specimens consist wholly of the pure mineral, the crystals varying greatly in size in different speci- mens, and the whole forming an exceedingly hard, compact mass. Other specimens show mixtures of the mineral with albite, chlorite, garnet, or actinolite, mica, and quartz. One large detached rock * Report Cal. State Mineralogist (1884), p. 182. t+ Monograph XIII, U. S. Geol. Survey, p. 76. 336 University of California. [VoL. 2. mass, some twenty feet long by six in thickness and five in width, illustrates the occurrence of the mineral zz sztu. This formed an exceedingly compact rock, composed for the most part of the rela- tively large crystals of the blue hornblende arranged without any common orientation and associated with garnet, chlorite, actinolite, titanite, and albite. The chlorite and actinolite were frequently localized in certain portions of the rock, forming areas of as much as ten centimeters in thickness; the other minerals were more gen- erally distributed through the entire mass. It was from this aggre- gate that the specimen of actinolite already described was obtained; it also furnished one of the specimens used for the study of the blue hornblende and of the chlorite described later on. General Description,—Weathered surfaces of the rock were lus- terless and of a dark gray color, but freshly-exposed portions pre- sented a blue-black color, and showed no evidences of decomposi- tion. Associated with the hornblende were crystals and angular fragments of titanite, often several millimeters in length. The latter mineral, however, was badly decomposed, consisting of a light yel- low opaque mass, though the inner portions of some of the larger crystals were transparent and of acharacteristic reddish-yellow color. Sections of the rock showed a complex intergrowth of the horn- blende crystals, together with small amounts of actinolite, chlorite, and titanite. The hornblende appeared in either rectangular or rhombic areas, and were easily distinguished by their strong pleo- chroism. Inclusions of titanite were sometimes observed. The second specimen examined was a compact polished boulder, com- posed of fine needle-shaped crystals arranged with their longest axes in approximately the same plane. Sections of this showed the entire absence of other minerals either as inclusions or as intergrowths. From the first specimen a few perfect, columnar crystals, some three to five millimeters in cross section and two centimeters in length, which had partially weathered out from the rock mass, were obtained. These presented only prismatic and _ clinopinacoidal faces. Though too dull to give good reflections, an approximate measurement of the prismatic angle gave the value 125° 14’. For the mineral crossite, Palache obtained the value 126° 6’, and for BLASDALE.] Contribution to Mineralogy. 307 typical glaucophane Bodewig found 124° 51’. Strongly-developed prismatic cleavages are shown in all sections of the mineral. Optical Properties. tions were cut parallel, or as nearly so as the nature of the material From some of the most perfect crystals sec- would permit, to the clino- and orthopinacoids. The former extinguished light at an angle of 8° with the cleavage trace and in convergent light gave no interference figure. This position was shown by the use of a quarter-undulation mica plate and also of a plate of gypsum, both of known orientation, to be the direction of least elasticity, in which respect the mineral differs from crossite and agrees with glaucophane, though the extinction angle is greater by two degrees than in any specimen of that mineral which has been examined thus far. Sections cut parallel to the orthopin- acoid gave parallel extinction, and with convergent light gave only a broad brush of interference colors. The optical orientation is, therefore, the same as that found in the majority of hornblendes, that is, ¢:c = 8°, though in the absence of terminal crystallographic planes the exact position of ¢ can not be determined. The pleo- chroism is the most pronounced optical feature of the mineral and furnishes the most valuable criterion for its identification. The color of the ¢ ray is bright sky blue to deep blue, of 6 purple to violet, and of a colorless, or a very faint yellow. In these respects the mineral closely resembles glaucophane, but differs from crossite. In some crystals certain localized areas presented a light green color, probably-due to the presence of actinolite, though no very definite line of separation from the main portion of the crystal could be distinguished. Chemical Properties —A portion of the first-described specimen was crushed in an agate mortar, and treated with hydrochloric acid, washed, and dried, and that portion which passed through an eighty- but was retained by a one-hundred mesh sieve, separated from the remaining titanite by means of Klein’s solution. The purified material had a specific gravity of 3.119. The second specimen was ground for analysis without further preparation; it gave a specific gravity of 3.116. The finely-ground material, which is of a blue- gray color, fused readily with the formation of a dark glass, and was scarcely attacked by strong acids even after long boiling. 338 University of California. [VoL. 2, TABLE No. III. Analyses of Blue Hornblendes. I | 2 3 4 5 6 7 8 NOL OR se teawessceess 54-52 | 52.39 | 57-67] 55.64] 56.49| 57.81 | 55.02 55.06 PATR@ sates aces ct 9-25,| I1.29)|| “10-07 || 15.11 |) 12-239) 12.03%) "ATS -49 Fe, O3 4.44 | 3.74 3.20 BiOG! |hecesceee 2.17 | 10.91 15.48 1M! (Q)oeenas aeesopac 9.81 |. 9.13 9-68 6.85 | 10.91 5-78 | 9.46 7.40 Mics Oe ere cere ceae fe ye%e) || Ie set7/ 9.85 7.80 | 7.97 13.07 | 9.30 11.49 Cal Ouse licen cee 1.98 | 3.03 95 2.40] 2.25 2.20} 2.38 -98 INI (Ol) Soksese tiene: 7-56| 6.14 6.80 9.34| 9.28 || GAP 6.38 KG RO eaees cance es .16 trace 2A2)\|\, assivrecsel|sececoe ssi) ecpdaneiee 27 .80 EV Ovat 1OOetralteeoencssee | Sieacnens EL24) gicaeccved|usseosteall Aeseeseees WNGEt IN eeesess H,O above 100° Teal) 2e5'7 2304) Meyer coaallaesccses|' Geeeccesc|eseeceee 1.98 AG TO esr a6iS) |i SUL). oeonacon ssasaseeleccsssusd|,) orezeeecsl | uescorcee |leeeeeeeaes Minis ©) ier care eesss 46 | trace] «6 56 | 50] seseeeers tracCe. |Meat 100.68 99.80 | 100.18 | 100.78 99.63 100.39 | 99.70 |. 100.06 ' Cont . Glaucophane from Syra, Luedecke, Zeit. d. Deut. Blue hornblende from rock, San Pablo, Galion Blue hornblende from boulder, San Pablo, California. . Glaucophane from Syra, Washington, Am. Journ. of Science [4], 40, vol. 11, p. 4o. Geol. Gesellsch, Band 28, S. 252. Glaucophane from Syra, Schnedermann, Journ. fiir Prakt. Chemie, Band BAIS 2385 Glaucophane from Zermatt, Bodewig, Pogg. Annalen., Band 158, S. 228. Crossite from Berkeley, this Bulletin, vol. 1, p. 188. . Glaucophane from Syra (Rhodus), Toullon, Sitzb. Akad. Wein., Band TOONS sie TABLE No. IV. Calculations Leading to the Formula of the Blue Hornblende. | | . | Elementary | Atomic Atomic wy Elemente ic i Analysis 1. foreeenty | guotient mae Analysis 2. CPG guotient Raan | | Si O, 54.52 | Si 25.64] .9098! 25. SiO> 52:39) Si02 4203 .8740 | 25. Al, O3 9.25 | Al 4.91 .1824 5.01 | Al,O, 11.29 | Al 5.99 .2225| 6.36 Fe,O3 4.44 | Fe 3.11 .0559 .t5 | Fe, O; 3.74 | Fe 2.62 .O471 1.35 FeO 9.81 | Fe 7.63 1372 3.76 | FeO 9.13| Fe 7.10] .1276| 3.65 Mg O 10.33 | Mg 6.23 2585 7.10 | Mg O11.37 | Mg 6.85 2842| 8.13 CaO. 1.98) Ca 1.41 .0354 .97 |CaO 3.03 | Ca 2.16 0543 1.55 Na, O 7.56 | Na 5.61 .2452 6.73 || Na, O 6.14 | Na 4.56 1993 5.70 K,O *10)]| Ko 3 .0033 £09/:| K,'O trace: || ...i..25.5: |B ceconces Namrreeen Hs. © 1.78)\ El) 207-2000 5.49 ||H,O 2.57|H .29 2900 | 8.29 TiO; .39|| Ti 424 |) “aos 14 || TiO, .14 | Ti .o8 0017 .05 MnO .46|Mn_ .36 | .0066 -18\ || Min O'trace: || (.ci.cccecccal! | ancoeseeslllieeeoees Seeneeecemes tanec © 44.53 | 2.8042) 77-00: ||.....2:----5-2+--s| ©) 45.72) |) 210700 oOs73 BLASDALE.] Contribution to Mineralogy. 339 The results of the analyses of the two specimens are given in the first two columns of Table III; for comparison five analyses of glau- cophane, four from the type locality of Syra, and one from Zermat, also the analysis of crossite, are included in the same table. In both of the analyses here reported the close relationship of the mineral to typical glaucophane is apparent. The only features worthy of especial note are the relatively large amounts of combined water and titanium. The latter element is easily accounted for in the first analysis by its inclusions; probably these were also present in the second specimen but escaped detection. Apparently the water is due to hydrogen which displaces the alkali metals to a certain extent as in the actinolite. Even larger percentages of water (namely four) are reported by Barrois.* Compared with the analysis of crossite, striking differences of the sesquioxide content are worthy of note. From a chemical standpoint the most impor- tant difference between the two minerals consists in the substitution of nearly equivalent amounts of ferric oxide for alumina. Presum- ably this difference is directly connected with the difference in the optical orientation, and though the data is too incomplete to be con- clusive, there are indications that there is a direct connection between the position of the acute bisectrix and the relative amounts of ferric oxide and alumina. In this connection, analysis No. 8, representing a variety of glaucophane from Syra (Rhodus), is of especial interest; the difference in the relative percentage of the sesquioxides is here even more strongly accentuated, but, unfortu- nately, no account of the optical properties of this variety appear to have been published. In Table IV are given the calculations leading to the formula of the mineral. It will be noted that the ratio of oxygen to silicon is in both analyses slightly greater than corresponds to a metasilicate. If, as in the actinolite, we represent the diad metals by. RY’ the elements HH, Na, K, AlO, Fe’’O by R’, and by Xa mixture of Si,O, and SiO, in nearly equivalent proportions, but with a slight excess of SiOQ,, the composition of the two samples would correspond to the formulas R/19.). Xi25 R’iga and R’15.95 * Barrois, Comptes Rendu, Tome 103, p. 221. 340 University of California. [Vor. 2. Xyes R’oo, which are fairly well represented by the following formule: I II RMR”, | =R’19 X11 R99 boo ke = 45 RXR YS sR’, XR’, f TR 3XuR’e2 TREMOLITE. At a single point in locality B contact between the schist and serpentine was observed. Between the beds of dark-colored serpentine and schist here found, a thin layer of a light-colored fibrous mineral was noted. Its contact with the serpentine was distinguished by a series of curved and moulded surfaces, clearly indicating the action of heavy pressure at this point. On the other hand, the mineral was associated with actinolite and glauco- phane, and intergrowths of the light-colored mineral and the more coarsely crystalline actinolite were observed. The pure mineral occurs in masses of fibrous crystals of pure white to light gray-green color, which show a pronounced schistose structure. It is easily crumbled into fine needle-like crystals, which are too small to be studied without magnification, but are TABLES No: Ve Analyses of Tremolite, Chlorite, and Talc. I 2 3 | 4 SO csstaesscassscavaossecss 56.68 27.38 27.03 | 56.02 Al, O 1.79 26.15 20.07 g.02 Heo (Os. ccecesrewsaceeec exsee 1.70 | 78 4.72 1.10 INCU @)\ cscdesdeie ces sere seas: 2723) 12-70 16.47 5.14 IEE O aepery eoncaneaccooiceee 19.35 18.92 18.90 24.10 CaO’ Cissscssseescsseeusces: T5 SOPs |) aeedetareray Ul) eacscome cee: | 60 INalgt Ol s ceeani tees cannes raccee We? Caiotee owe 1.15 72 | Loeeennee KG Gas cccccteetec secant i) eerie oe oe | Se een, | L:22 | sdeet ates lel yO) alle adele oacecen beanie: 530) TSE "i ® \oecweacetese | .16 Hs @ above 100% 2.1, 2.25 11.44 11.78 4.34 | 99.90 100.03 100.91 | 100.48 | . Tremolite from San Pablo, California. . Prochlorite from San Pablo, California. . Prochlorite from Austria, Vuylsteke, Tscherm. Min. Mitth, N. F., Band 2 OA 4. Talc from San Pablo, California. Oo NA _ BLASDALE.] Contribution to Mineralogy. 341 then easily shown to be lacking in definite crystallographic planes. Many of these extinguished light parallel to their longest axis, but others gave extinction angles of as much as 4°. The specific gravity of some of the separated crystals was found to be 3.986. The composition of this mineral, as shown by the analysis reported in Table V, is clearly that of tremolite. It presents no unusual features except the rather high percentage of lime and combined water. CHLORITE. As previously noted, chlorite is a common associate of the actinolite. Aside from its occurrence in the actinolite boulders, it fills lenticular cavities and veins in the schist; its occurrence in relatively large masses in the glaucophane rock has already been alluded to. Material from the latter source only was examined. It here assumes the form of a scaly-grained dense mass composed of comparatively thick groups of cleavage flakes, the masses being disposed without common orientation. The maximum surface presented by these flakes did not exceed a square centimeter. In some cases the mass parted in such a manner as to give rise to more or less conchoidal surfaces. Crystallographic planes were entirely absent. The cleavage flakes were comparatively trans- parent, were of a yellow-green to olive-green color, though on exposed portions red stains due to oxidation were very apparent. They extinguished light like an isotropic medium. The specific gravity of a portion weighing about twenty-five grams was found telbe=2.702. Portions from the interior of the mass and as free from oxida- tion as could be obtained were used for the analysis reported in Table V. The high percentage of silica and the other features of the analysis at once show that it is prochlorite. It may be com- pared with a specimen of that mineral analyzed by Vuylsteke, which is reported in the fifth column of the table. TAIEC, Talc forms white or apple-green masses filling the interstices between the actinolite crystals and is occasionally found in com- 342 University of California. [Vot. 2. paratively large masses in the crystalline schist. Though entirely amorphous, some fragments show suggestions of a scaly structure, and in such cases have a mother-of-pearl luster. Material from a boulder obtained from locality A, which was selected as carefully as possible but was probably not absolutely free from very fine actinolite crystals, gave the analysis recorded in the fourth column of Table V. The analysis is remarkable in the comparatively low magnesia and the very high iron and alumina; in fact, in both of the latter figures it exceeds any of the analyses of this mineral of which I have record. The analysis, together with the scaly structure previously alluded to, suggests that the mineral has been derived from chlorite. DIALLAGE. This forms a light-colored friable rock which is of rather fre- quent occurrence in both of the localities here considered, being found both as detached fragments and as groups of massive boulders, the latter probably zz sztz. The specimen examined was obtained from locality B. Structurally the rock is composed entirely of flakes or lamellae, which often present several square centimeters of surface and are distinguished by their greenish-yellow color and dull, non-lustrous character. True crystallographic planes were never observed, but the lamella were often divided by a series of more or less pronounced cleavages into prismatic fragments, some- times suggesting a fibrous structure. The lamellz show parallel extinction and with convergent light the eccentric emergence of an optic axis, but a section cut approximately parallel to the prismatic cleavage gave an extinction angle of 7°. It is clear then that the lamella represent orthopinacoidal cleavage flakes of a monoclinic pyroxene. A series of transverse partings traverse many of the lamelle, but there is no visible evidence of alteration, nor were inclusions of other minerals observed. The interference colors are of a high order. The chemical composition of this substance, as shown by analysis in Table VI, is clearly that of diopside, while its structural features class it as diallage. It showsa remarkably close agreement with a sample of diallage from Scotland, analyzed by Heddle, the BLASDALE.] Contribution to Mineralogy. 343 result of which is reported in the same table. The only note- worthy features of the two analyses are the presence of the alkali TABLE No. VI. Analyses of Diopside, Serpentine, and Albite. I 2 3 4 5 Sti @ givers saaieececssameces 51.91 Se 77 49.62 33.66 67.09 Al, Os; 3.55 2.10) || 2.97 1.36 20.47 Fe, O3 1230) 1] icesecatvers 2.49 BAN casteeeeee MG" OM i seicesecsseceeweestes 2.65 2.96 2.99 ASSO" Vetererees Moi Ore tye age aaeces vance as 16.15 18.46 19.72 38570.) secnanece CANON sieeesscs se terscones 22.85 22.10 19.14 48 24 INapi@ierncctasctsesseosnaners 56 58 60 98 10.96 K, O eccccrecccseacsecenssese| eseeevess .63 Saletetwlcwen | 00) Biswine=t'a steel ||) Uaesiviestris'se lil (CO) Ee titole\ Ai ans aacesoos a2 dectaee’ |) sdaeiscoats 22 27 H, O above Ico®%.... ... .86 1.08 291 | 19.70 59 ADI Oe ae cecces sauces sae se TOC vlip ursturevcerss || eieeesccceuil) mmcrscen sec uemmcrsecees Min O Rak cstrce cocsaueecss 233 31 i trAGG Nl Kawenscs. 100.47 99.99 100 24 100.26 99.62 1. Diopside (diallage) from San Pablo, California. 2. Diallage from Scotland, Heddle. Trans. Royal Society, Edinburgh, vol. 28, p. 464. 3. Diopside (altered) from San Pablo, California. 4. Serpentinized anthophyllite from San Pablo, California. 5. Albite from San Pablo, California. metals, and of combined water. The specific gravity of the rock is 3.183. The latter fact, together with the large amount of com- bined water, probably indicates the beginning of the process of alteration to serpentine. ALTERED DIALLAGE, A rather coarse-grained mottled rock, found in relatively large masses 77 sifu, especially from locality B. It is easily broken into irregular fragments which present plane or curved surfaces, either light yellowish-green or blue-black in color. Thin sections of the rock show areas of a light greenish-yellow, striated mineral and especially at the angles between these areas veins or masses of a black opaque mineral. Magnification of the light-colored areas shows that this mineral is closely related to the diallage previously 2 344 University of California. [Vor. 2. described, the structure, color, transverse partings, and extinction angle all indicating this fact. In some instances, along the cleavage cracks, darker-colored cloudy areas, evidently marking the begin- ning of alteration, may be observed. The dark-colored areas are resolved into a dark brown somewhat opaque ground mass, and veins composed of grains of magnetite. Apparently they represent those portions in which, on account of the relatively large amount of surface exposed, alteration has been most complete. The blue- black surfaces of the rock are due entirely to veins of magnetite. Specimens collected from the same locality show still further devel- opment of the process of serpentinization. The chemical investigation of the rock, the results of which are recorded in the third analysis of Table VI, confirm the above theory. The decrease in silica and lime and increase of combined water and magnesia, clearly indicate the progress of the process of serpentin- ization. The specific gravity of the rock is 3.153. SERPENTINIZED ANTHOPHYLLITE. This occurs in groups of massive boulders, often rounded but more commonly angular, which outcrop at several points in local- ity B, often projecting to the height of twenty feet above the pre- vailing level and suggesting the character of intrusives. The rock is exceedingly tough and compact, and does not fissure readily. The outer surfaces are of an ashy gray color but freshly-exposed portions present yellowish-green cleavage planes or curved surfaces of a light brownish-yellow. Thin flakes of the mineral possess the yellow translucent features characteristic of serpentine, but on the whole the rock possesses few of the more obvious features charac- teristic of that mineral. Microscopic examination shows for the most part a fibrous mineral which is distinguished by its high inter- ference colors, parallel extinction and correspondence of the direc- tion of least elasticity with the cleavage trace. These features all indicate the mineral anthophyllite. In addition there are found considerable amounts of serpentine, grains of magnetite and fine veins of calcite. For the chemical examination a mass bounded by freshly- exposed surfaces only was employed. The finely-ground powder BLASDALE.] Contribution to Mineralogy. 345 was partly decomposed by hydrochloric acid after long digestion, The analysis reported in Table VI shows a remarkably high percent- age of combined water, which can scarcely be accounted for unless the existence of a hydrated anthophyllite be admitted. The specific gravity was found to be 2.756. ALBITE. This mineral is found in the crystalline schists, especially those containing quartz and glaucophane. In one mass of these schists from locality B there is present a vein some six inches in width and visible for a distance of some twenty feet, which consists of crystals of the pure mineral. They are uniformly twinned according to the albite law, but are too opaque to admit of microscopic investigation. The analysis recorded in Table VI shows that the mineral possesses no unusual features but clearly indicates that the process of kaolinization has begun. NOTE ON THE PROBABLE RELATIONSHIPS OF THE ABOVE MINERALS. Though aside from the principal objects of the present paper, some observations on the occurrences and probable genetic relationships of the minerals here described are not out of place. The physiographic features of the principal locality represented (B) may be briefly described as a gentle hill slope extending from the top of the ridge which forms the western wall of Wildcat Cafion, to the alluvial plane surrounding the Bay of San Francisco. It is transversed by numerous small water courses, which are rapidly sculpturing the slope into a series of distinct hills. The principal rock formations represented are serpentine in its various forms and a series of crystalline schists, both of which for- mations outcrop at various points over the entire surface, but are more strikingly revealed in the form of projecting masses or ledges, sometimes extending to a height of twenty feet above the prevailing slope. Various stages in the alteration of pyroxenite, the ultimate result of which is serpentine, are to be found, but the latter often assumes the form of compact blue-black 340 University of California. [Vor. 2. masses which are probably derived from peridotite. Ledges of the serpentine weather out into most fantastic forms, composed of a porous, kaolin-like material, in which all evidences of the orig- inal structure have been lost. They are not infrequently trav- ersed by veins of quartz, some of which is coarsely crystalline. The crystalline schists also present many variations in structure and composition, the most striking features being a tendency for the segregation of the constituent minerals into fairly homogeneous pockets or veins. Practically pure masses of actinolite, glauco- phane, chlorite, talc, albite, and quartz may be obtained from the same rock mass. Gradations between such occurrences and the strictly schistose portions, composed of finely crystalline minerals only, are to be found. Evidences of crumpling and distortion of the mass after crystallization has taken place are revealed by deformations (curvatures, twistings, partings, etc.) of the individua crystals and by the curvature of the plane of schistosity itself. The true connection between the two formations is an obscure one. Contact between the two was observed in a single instance, and that of a rather indefinite character, the only feature worthy of note being the tremolite which has been already described. The chemical features seem to show that there is a general relationship between the two formations, since both groups of rocks repre- sent magmas, comparatively rich in magnesia and lime and poor iniron and alumina. The rather unusual occurrence of soda in the pyroxenite also indicates a relationship with glaucophane- and albite- bearing schists, but there seems to be, as yet, no means of determining the exact nature of this relationship. The occurrence of actinolite in the form of nodules many of which are rounded and polished, though said to be not uncommon in the Coast Ranges, is, on the whole, an unusual one,and suggests an inquiry as to the geological peculiarities to which this feature is due. Two possible theories (one chemical and the other dynamical) suggest themselves. According to the former theory, the nodules arose from peculiarities in the composition of the peridotites and pyroxenites which preceded the serpentine, whereby from certain centers of crystallization spherical aggregates were formed and segregated as definite structures in the subsequent disintegra- BLASDALE. ] Contribution to Mineralogy. 347 tion of the rock. This theory would explain their rounded charac- ter, and is supported by the occasional occurrence of nodules with indications of sucha center of crystallization, but other facts are not in harmony with this view. The evidence seems to point to the fact that the actinolite is all derived from the crystalline schist. In no instance were the nodules found in the serpentine, and there was a striking absence of actinolite-containing fragments below the serpentine areas. Also the characters of the actinolite from the schist and from the nodules are identical, the variations in the form and size of the crystals, their deformations (curvatures, etc.), are repeated in both, the chemical composition is essentially the same, and the associated minerals show the same range of variation. There is, however, insufficient evidence of the separation of the nodules as distinct structures in the original schist, though sugges- tions of this are furnished in the lenticular or pocket-like masses occasionally encountered. A dynamical theory would require the action of forces capable of disintegrating the schistose rock, and of grinding or shearing forces capable of rounding and polishing the more or less angular fragments thus produced. Examination of all the actinolite- containing fragments of a given area shows that only a part of these have attained the perfect boulder form; they are often present as angular or only partly-rounded fragments, many of which show a suggestion of the schistose structure. Furthermore, those areas which show the greatest number of perfect actinolite boulders also show rounder masses of other minerals (glaucophane, etc.), though the former are decidedly more frequent. The latter facts may be due to differences in the resisting powers of the differ- ent minerals to the agencies concerned. The nature of the agency concerned in such a grinding and polishing process is somewhat difficult to indicate. Streams of water of high velocity could readily accomplish the desired result, and occasional boulders, which were found in the bottom of stream beds, possessed the rounded and polished character in a high degree, but, presumably, this agency is of too local a character to account for all the phe- nomena. Aside from this there is evidence of intense movement and shearing action of the rock mass in the crumpled character of 348 University of California. [Vor. 2. the schists, and it is evident that much of this transpired after the separation of the actinolite crystals. It would clearly require, how- ever, a long succession of such movements to produce the phenom- ena here observed, and satisfactory evidences of this are not present, nor could it have been expected that they would have been retained. University of California, October 28, TQOL. Nae. UNIVERSITY OF CALIFORNIA , Bulletin of the Department of Geology ; Vol. 2, No. 12, pp. 349-450, Pls. 10-17, Map. ANDREW C. LAWSON, Editor The Berkeley Hills A Detail of Coast Range Geology BY ANDREW C. LAWSON and CHARLES PALACHE FA Ss Lo eS wl, VG se os | Ri , IW . | a Sere 4, <= FE the chief axis in clinopinacoidal sections was 44 degrees; the average of seven readings was 41 degrees. Twinning is very common accord- ing to the augite law, the twinning plane being the orthopinacoid, The twins consist of two individuals, separated generally by an irregular surface, or of many broad and narrow lamelle irregularly alternating, thinning out or ending abruptly in the middle of the crystal. In one case a twin was observed composed of many lamella, in which the twinning plane appeared to be the basal plane. Several intergrowths of augite and hypersthene were observed, the augite always inclosing the hypersthene as a periph- eral zone. The two minerals have their chief axes in common, and are separated by an uneven but perfectly distinct line. Inclu- sions of glass in rounded blebs and magnetite in grains and crystals are common, and needles of apatite were noted. Decomposition of augite to serpentine is not rare in these rocks. The serpentine develops about points in the center or on the periphery of the augite crystal, forming sharply-defined areas from which strings and bands of the serpentine extend: into neighboring cleavage cracks. It is a finely-felted or fibrous form of the serpentine, in which, when replacement is complete, no definite remains of the structure of the augite can be detected. One crystal of augite was observed to be partly replaced by calcite. Chlorite is rarely present in scaly aggregates, mingled with serpentine in decomposed areas. It appears to be an exceptional product of augite alteration. The augite of the ground-mass is invariably in the form of small, rounded grains, which are identical in color and optical properties with the augite of the phenocrysts. These grains fill the interstices between the feldspar microlites, which they nearly equal in bulk. The occurrence of augite as inclusions in the feldspar phenocrysts has been described. Hypersthene is a constituent of one phase of the andesites, but is present in small amount. It forms imperfect phenocrysts of 416 University of California. [Vot. 2. prismatic habit, showing characteristic prismatic cleavage and trans- verse basal parting. It is nearly colorless and is weakly but dis- tinctly pleochroic :¢=pale greenish; a=6=pale reddish yellow. Its intergrowths with augite have already been noted, hypersthene in all cases being the older mineral. Many of the crystals exhibit a network of cracks, which give a granular appearance to the sur- ace. This condition is accompanied by and seems to precede a decomposition into serpentine. The weak pleochroism of the hypersthene suggests that it is a variety of the mineral with low content of iron, an idea confirmed by the absence of dark borders of separated iron oxide about decomposed crystals, which appears to be acommon characteristic of normal hypersthene in andesitic rocks. Olivine, like hypersthene, is a sparing constituent of certain facies of the andesites, and, so far as observed, the two minerals do not occur in the same rock. While the evidence on this point is, of necessity, only negative, and therefore not conclusive, it suggests that olivine is formed at the expense of the hypersthene, or, vice versa, as local conditions may determine. This example confirms the opinion expressed by Zirkel * on this point. Olivine occurs as idiomorphic phenocrysts of characteristic form and properties, commonly much altered to serpentine. As the mineral is fully described under another group of rocks in which it is an impor- tant constituent, it will receive here but -passing mention. Magnetite is abundantly present in all facies of the andesite, particularly in those containing the least proportion of glassy base. It is found in porphyritic individuals of varying size, with irregu- lar crystaliine form, in crystalline grains as a constituent of the ground-mass, and as inclusions inall the other porphyritic constitu- ents. It is also sparingly formed as a secondary product through the alteration of olivine and augite. Apatite is a constant constituent of the andesites. It is seen included in feldspar and augite in slender, colorless prisms, with hexagonal cross sections and characteristic optical properties. In certain facies of the rock apatite assumes a different appearance. It forms rather stout prisms with irregular terminations and hexa- *F, Zirkel Lehrbuch der Petrographie, Leipzig, 1894, I, p. 813. ef pee The Berkeley Hills, ~ 417 gonal sections, grayish in color and showing distinct pleochroism in tints of bluish gray and pale yellow, the absorption being e » o. Its color seems to be due to the presence of minute rod-like inclusions arranged parallel to the prismatic axis of the crystal. These pleochroic crystals occur alike, included in feldspar and augite, and embedded in the ground-mass. Glass is a variable constituent of the andesites. Its color varies from colorless, through greenish and yellowish tints, to a deep brown or almost black. The opacity is due to clouds of minute- dust-like particles, which, as they occur likewise in adjacent feld- spar crystals, probably consist of submicroscopic individuals of magnetite. They may, however, in part be of globulitic character. Besides forming a constituent of the ground-mass of some facies of the rock, glass is widely distributed in the form of inclusions of porphyritic crystals of feldspar and augite. Of the secondary minerals whose origin may be clearly traced to the original constituents of the rock, serpentine is the most abundant. In color it is greenish to bright or brownish yellow and is non-pleochroic. In ordinary light it appears structureless, but in polarized light it breaks up intoa finely-fibrous felted aggregrate, polarizing in pale bluish tints, or sometimes quite isotropic. The color appears to be due to the presence of ocherous iron oxide, probably separated at the time of the formation of the serpentine from its parent mineral. It is found partially or wholly replacing pyroxene and olivine phenocrysts, in cracks and cavities in feldspar and replacing portions of ground-mass. Occasional crystals are seen of a mineral of serpentinous aspect which appears to be allied to iddingsite; it will be fully described in another place, it being more characteristically developed in the basalts. Chlorite and calcite have been shown to occur very sparingly as alteration products of augite, Limonite occurs abundantly in one facies of the andesite in grains and shreds throughout the ground-mass, and as the filling or lining of cracks, where it forms mammillated coatings. It is clearly secondary, but its immediate source is not evident, as it permeates all the constituents of the rock. It also occurs widely dissemi- 418 University of California. [Vor. 2. nated as a coloring matter of the serpentine and other minerals, in all forms of the andesite. Analcite has been mentioned as forming interesting replace- ments of feldspar. This has taken place. in a brecciated andesite, the fragments of which have been largely cemented by analcite, which has also crystallized in vugs and open cracks as brilliant and perfectly-formed trapezohedrons. Thin sections of the rock show that most of the feldspars are wholly or in part replaced by anal- cite, the alteration having taken place from either the center of the crystal, leaving at times a narrow peripheral rim of undecomposed feldspar, or more commonly by an irregular invasion of the crystal from various points, in which case isolated cores or shreds of feld- spar can still be detected. This change affects both phenocrysts and microlites, and appears to be accompanied by the formation of calcite, presumably from the calcium liberated from the plagioclase. The analcite is water clear and wholly isotropic. It was readily decomposed _ by acid applied to the surface of the thin section, but did not gelatinize,as analcite is said to do by Rosenbusch. The silica separated as a powder which would not hold the stain of the fuchsine solution applied to it. One of the crystals was found to have a specific gravity of 2.256. Analcite is also found in amygda- loidal cavities in one facies of the rock. The remaining minerals mentioned as occurring in the ande- sites, calcite, chalcedony, opal, quartz, and natrolite, all occur as the amyegdaloidal fillings of cavities ina single facies of the rock, and will be best described under that head. The Amygdaloidal Andesite—We may now proceed to the description of the structural and other microscopic features of the andesitic rocks, not, indeed, dealing with each particuiar lava flow, but rather characterizing the chief varieties into which they may be classed. One of the most prominent of these varieties is that which, under the designation of the “amygdaloidal andesite,” has been described as the basal member of the volcanic portion of the Lower Berkeleyan. The general macroscopic features of the rock have been already sketched in the description of its field occurrence. It is a dark gray to black, compact rock of amygdaloidal habit, which is readily distinguished from the other lavas of this field. es The Berkeley Hills. 419 Under the microscope the thin sections exhibit a hypocrystal- line structure with occasional porphyritic crystals. These pheno- crysts, of which more than two or three seldom occur in a slide, consist of labradorite feldspar and augite in idiomorphic crystals. The ground-mass is a uniform mixture of feldspar microlites, grains of augite, and interstitial glassy matter in nearly equal pro- portions, with scattered grains of magnetite. The microlites show more or less perfect flow structure and are tangentially grouped about the vesicles, which are frequently drawn out into long wedge- shaped forms, clearly by differential movements of the viscous magma. The vesicles are generally filled with secondary minerals, thus forming the amygdules, which give the rock its distinctive aspect. These amygdules are of all sizes, from that of a pin head up to six inches in diameter, the average size being less than an inch across. Their shape is infinitely varied. The more regular forms are spherical, ovoid, or disc-shaped, cylindrical, wedge- shaped, or almond-shaped; irregular and fantastic shapes are quite as numerous, especially in the more highly vesicular lavas, where the vesicles have moulded one another in. expanding. Most of them, however, are chalcedonic only in their outer part, and are then lined with clear vitreous quartz crystals, leaving a cavity at the center, or are filled in solidly with quartz of the same character; or the quartz at the center may be asugary aggregate. When hollow and lined with brilliant quartz crystals, the latter are often remark- able in being terminated by the positive rhombohedron alone. The centers are sometimes filled with large crystals of calcite, and that mineral has in some cases formed the first layer in the cavity, followed by chalcedony. When such forms are exposed to the weather, the calcite is quickly dissolved, and leaves the outer sur- face of the chalcedony covered with sharp-cut moulds of the cal- cite crystais. Calcite forms the sole filling of some cavities. Natrolite occurs frequently alone, and with calcite, chalcedony, and opal, in these amygdules. It is always finely fibrous in radial aggre- gates. Under the microscope it is cloudy, owing to its exceedingly fine fibration, gives rather high interference colors, and extinguishes parallel to the fibers, the radial form giving neat interference crosses in parallel polarized light between crossed nicols. It gelatinizes 420 University of California. [Vot. 2. readily with hydrochloric acid. When associated with them it was formed after calcite and opal, and before chalcedony. It was not seen in the same cavity with analcite, though the two minerals occur in adjacent amygdules. Analcite occurs either alone or crystailized simultaneously with calcite. Its properties have already been described. Opal forms the filling of the veinlets already mentioned as frequently traversing the rock, and is the earliest deposit in some amygdules. It is colorless and_ slightly doubly refracting, the spherical masses exhibiting a dark interfer- ence cross.* A bright green mineral was observed in some amyg- dules, forming an exceedingly thin external coat. A thin section of one of these showed the outer layer to be of opal stained with a green coloring matter of undeterminable character. Chalcedony is, as above stated, very abundant in the amygdules, and exhibits characteristic optical properties. It was deposited after opal, natro- lite; and some calcite, and before quartz and some calcite. It has been shown that the amygdaloidal facies occurs over a large area, and is characterized throughout by the presence of secondary minerals, of which silica in various forms is far the most abundant. As the rock itself is comparatively unaltered, it could not have furnished the great amount of silica thus present, and it is a matter of interest to seek the extraneous source of supply capable of furnishing that substance in sufficient quantity and uniformly over so large an extent. Such a source is probably to be found in a bed of very acid volcanic tuff which commonly over- lies the amygdaloidal rock. Circulating waters would readily dis- solve silica from this tuff whose porous structure would facilitate such action, and under slightly different conditions of temperature or pressure they would deposit the mineral in the vesicles of the underlying bed of andesite. The Grizzly Peak Andesite, Porphyritic Facies.—TYhe next most important variety of andesite is that which we have described in the account of the stratigraphy as the ‘‘Grizzly Peak andesite.” There are two rather distinct facies of this andesite lava; the lower flows, being holocrystalline and laminated, are referred to as the holocrystalline facies, and the upper flows, being distinguished by *Rosenbusch Mik. Phys., pp. 122 and 89g. Decne | The Berkeley Fitts. 421 a prevailing porphyritic habit, are referred to as the porphyritic facies. Together they make up the greater part of the basal vol- canic member of the Upper Berkeleyan. The*porphyritic andesite occurs typically along the upper part of the Frowning Ridge escarpment and particularly on Grizzly Peak, and will be first considered. It is, in the fresh condition, a compact massive rock of black color, with pronounced porphyritic habit, the phenocrysts being usually yellowish feldspars with occasional olivines. Under the microscope the porphyritic structure is strongly marked, large phenocrysts of feldspar, augite, olivine, and mag- netite occurring in a microlitic ground-mass. The phenocrysts exhibit striking evidences of the effect of mechanical strains in their very commonly fractured or fragmentary condition. Corro- sion and absorption of the earlier formed crystals by the magma is also evidenced. Nevertheless many of the phenocrysts are in beautifully sharp idiomorphic forms, and most of them are clear and unaltered. The feldspar, judging by the extinction angles, is an acid labradorite or andesine. It offers excellent examples of the inclusion of glass and augite, described on another page. The augite is of a pale green color, sharply bounded and little altered. Olivine is sparingly present in large, well-formed crystals, which are mostly decomposed to a bright yellow serpentine. Magnetite forms well-defined crystals of large size, and apatite of the pleo- chroic variety is quite abundant. The ground-mass consists chiefly of feldspar microlites of exceedingly small dimensions, with fewer augite granules, minute crystals of magnetite, and a variable but usually small amount of colorless glass. The microlites show a linear arrangement and are tangentially grouped about the phenocrysts, giving evidence of a fluidal structure, not visible in the mass of the rock. The red color of weathered forms of this facies is due to the setting free of hydrous iron oxide through the serpentinization of pyroxene and olivine. The resulting iron oxide as well as the serpentine pene- trates the rock in every direction along cracks and fissures, and ultimately penetrates its whole mass. The feldspars decompose to kaolin in the ordinary manner. Chlorite was not observed among the decomposition products in any of the sections prepared, but in 422 University of California. [Vot. 2. some hand specimens a bright green mineral, probably a chlorite, was observed in spots and bunches as a stain in the feldspars. Iddingsite, derived from the olivine, is very sparingly present. The rock thus described is an olivine-bearing augite andesite. It is thus classed largely on the basis of its chemical character, analysis showing that it is much less basic than the above minera- logical composition would lead us to expect, and clearly of ande- sitic composition. On Grizzly Peak and for about 100 feet below the summit, this facies of the andesite is exceptionally rich in glass in the ground- mass, while not differing greatly in its macroscopic aspect from that just described. In thin sections it shows more abundant phenocrysts. Considerable portions of this glassy rock, however, have been brecciated and extensively altered. The fragments of the breccia have lost their dark color and appear gray or white. This change is due to a process of opalization of the ground-mass. The paste in which the fragments are imbedded is similarly affected. Examined in thin section, it is found that the porphyritic crys- tals do not differ from those of the unaltered rock, but the ground- mass, while nearly isotropic, has a totally different appearance from the normal glassy base. It appears to be an impure opal, stained with iron oxide and other foreign matter. The brecciation is but faintly emphasized, the substance of the fragments blending indis- tinguishably with the cementing paste. To test the nature of the isotropic ground-mass, a portion of the rock was finely pulverized and boiled with caustic potash to extract soluble silica if present. By this means the presence of a large amount of soluble silica was shown, and the opaline character of the ground-mass was estab- lished. The substitution of opal for the original ground-mass of the rock must be considered as a result of local solfataric action. No further evidence of such action on an important scale has been observed within the area investigated. The Grizzly Peak Andesite, Holocrystalline Facies —This vari- ety of andesite is not so distinctly characterized as the two pre- ceding, exhibiting a greater variation of texture and a tendency to merge by gradations into the porphyritic facies. It is repre- PALACHE AWSON | The Berkeley Fiills. 423 sented by lavas of considerable volume and extent, but in its most typical cccurrence is found immediately beneath the lavas last described on the front of the Frowning Ridge escarpment. It also forms a large part of the Ruin Peak Ridge, on the northeast side of Wildcat Creek. It is generally characterized by a lamellar jointage, which has been described on a previous page. In hand specimens it is a dark gray to reddish brown rock of uneven fracture and rather coarse porphyritic habit. It is locally vesicular or amyg- daloidal. In thin section it presents a distinctly holocrystalline porphyritic texture. The porphyritic constituents are feldspar, augite, hypersthene, and magnetite, imbedded in a ground-mass of feldspar microlites, augite granules, and grains of magnetite. The plagioclase feldspar, judging from its extinction angles, is a basic labradorite or bytownite. It abounds in characteristic glass and augite inclusions, and shows little evidence of magmatic corrosion or mechanical fracture. The forms of the crystals are not so well defined as were those of the phenocrysts of the porphyritic facies. Orthoclase feldspar is probably present in occasional phenocrysts. The phenocrysts of augite and hypersthene are imperfectly idio- morphic. Augite is very much the more abundant of the two minerals. The feldspar microlites of the ground-mass are generally twinned and extinguished at angles which indicate that they have the composition of labradorite. They show an imperfect linear grouping suggestive of flow structure, but its expression is hin- dered by the abundance of the phenocrysts. Yellow ocherous serpentine, and a little calcite and chlorite, are the only secondary minerals present in the typical phases of the rock. The calcite is in some cases confined to distinct veins sometimes half an inch in thickness, in which it is crystallized with more or less quartz. The flow or klinker breccias which are associated with these andesite lavas are as usual more decomposed and altered than the massive lava. The fragments, being cften thoroughly vesicular, appear brightly colored, due to the oxidation of the contained iron. The thin sections of these breccias are much obscured by the abundance of iron oxide disseminated through the rock, but the coarser-textured masses seem to have the structure and general microscopic characters of the holocrystalline variety of andesite 424 University of California. [Vo. 2. modified by secondary action. Besides the iron oxide, opal per- meates the rock, filling cracks and considerable areas between the crystals. The cementing material is quite obscured by these sec- ondary products, but may, in part, be fine volcanic ash. It is in this andesite breccia that analcite was found cementing the frag- ments and replacing the feldspars as described on a previous page. The 20-foot lens of pale gray, finely laminated andesite which has been described as occurring between the holocrystalline and porphyritic lavas which make up the Grizzly Peak andesite belt, is allied in character to the variety next to be described, but, on account of its association, may be here referred to. In thin section the rock is seen to have a very fine granular structure, with occa- sional small phenocrysts of feldspar and augite. The ground-mass is chiefly composed of feldspar microlites and granules, with a slight admixture of augite and magnetite grains and little or no glass. The laminated structure so prominent macroscopically is evidenced in the slide by narrow zones traversing the rock at small intervals, in which the feldspar microlites are parallel, the intervening spaces showing no such grouping. The yellowish tint of the separation planes is seen to be caused by the concen- tration of a pale yellowish serpentine-like mineral along these zones, which imparts its tint to the feldspar, and thus appears to the eye to be crystalline-granular. Aphanitic Laminated Andesite.—This designation is applied to certain peculiar lavas which are prominently developed in the Campan basin, particularly on Pie Knob and Fog Bluff. The type is confined to the Campan series, in which they occur among the earlier flows. The rock is of a light gray to reddish color, with a well-defined lamination evidently due to flow. As a rule, it is quite aphanitic, although porphyritic crystals may be occasionally detected. Partings are not uncommonly developed along the planes of lamination, but between these the rock is compact in texture, although it may be locally vesicular. This rock seems to have been affected more largely by processes of alteration than any other rocks in the volcanic series. Large masses are seen seamed and fractured in every direction, and intersected by slick- ensided surfaces of greater or less extent. Secondary minerals Bain | The Berkeley Fills. Ags are very widely disseminated through them; limonite filling cracks and cavities, and in streaks following the planes of lamination; calcite abundant in veins and as the filling of vesicles; chalcedony and rarely analcite as amygdules in the vesicular forms; all these secondary products form prominent features in the macroscopic aspect of the rock. Under the microscope it is seen to be holo- crystalline, but very fine grained, porphyritic crystals being very. exceptional. When there are such, they are plagioclase and augite in imperfectly-formed crystals. The ground-mass is very feldspathic, containing, besides the feldspar microlites, augite granules, and magnetite in grains and rods. Here also secondary products are abundant and prominent. Limonite is in streaks, spots, and con- centrically-banded aggregates. Calcite replaces portions of the original ground-mass, and fills cavities in concentric aggregates, alternating with or surrounding limonite. Serpentine, ocherous from included iron oxide, fills interstices of other constituents, and replaces augite grains. Flow structure is well marked by paral- lelism of the feldspars and by their tangential grouping about phenocrysts and vesicles. The somewhat arbitrary division of the andesitic rocks into the four facies above named and described, is justified on grounds of convenience and simplicity. It is done, however, in full recog- nition of the fact that in this, as in every natural group of volcanic rocks, there exists a more or less uniform series of forms, merging one into another by insensible gradations. The frequent occur- rence of forms which can not be assigned with certainty to any of our types is sufficient proof of the artificial character of our grouping, which, notwithstanding, has its usefulness for purposes of description. It is altogether probable that a more extended study of the volcanic series over a wider area would not only increase the number of varieties in the andesite group, but would also reveal intermediate forms which would unite the andesites to the basaltic group by a graded series of characters. The intimate field relations of these two groups are such as to confirm the suggestion that, though now regarded as specifically distinct, they are essentially the different facies of the development of a single magma. 426 University of California. [Vor. 2. Chemical Characters —The chemical investigation of the ande- site group, while not so complete as would be desirable, is yet sufficiently extensive to bring out some interesting points of corre- spondence and gradation in character between its members, and to establish a good basis on which the group may be differentiated from the associated groups of basaltic rocks. Complete analyses of the four principal types of the andesite and two silica deter- minations were made and are exhibited in the accompanying table. Comparing these analyses it will be seen that the range of silica is not much above four per cent. It is noticeable also that of the other components the alumina is uniformly high and the iron oxide correspondingly low; the alkalies show but little variation in the first three analyses, but are notably small in VI while the lime is exceptionally high. This analysis shows the Pie Knob rock to be an exceptional type, and its classification with the andesites is recognized as questionable. The specific gravity appears to increase in proportion as the glassy constituent of the rock de- creases. The composition of the first three confirms their classifi- cation, already made on mineralogical and structural grounds, as pyroxene andesites. Analyses of Andesites. | I If. TDN: IV. Ne VI. Si Op». 59-75 59-74 56.81 57-58 60.79 50.47 Bi OPee trace trace ETACE, — || seccdedseasete son|iboceccescbecsedlMeemmeeneees Al, O3 19.08 19.94 TO36. rile ts eeae oo esta nace snemesteecee 22.55 eNO srl) mens. casnee 1.81 DA Se iil soceteeic ns weeeleotaccicmescces 95 HerOr =: 2.91 5.41 3:04 © Wasssesseesusecsellveszarsaccsenees 1.97 Mn O... trace trace EELACE) Ges cscecccesvccastl| ccsceceaccneceen aeceeeetees Ca O 6.15 3-74 GAB. fF Wiscsseesevscnuiecelccesee seenenees 16.89 Mg O 4.72 1.18 AVS eo 1 jhossachcheveastea|ecnacseesceetees 4.48 Na, O 4.31 4.65 AGUS a llaicct ances steelveveaeeh ieee ot 88 Keo Ov 92 1.02 DeQOe | il sadeenaccertcesl| tase ce semeemeen 2 dety (O}ere 15 35 FQ5) | illssedsinsleraicsvccts|lioscdactoas. etches eceimmeteen HETOr. 2.64 2.09 TilF 9 | ascvccuscsecesed| tsocobeeceaerenie 1.03 Total... 100.63 99-93 99-73 99-74 Op: 2.3 2.62 2.64 2.74 2.66 escarpment. Analyst, Palache. Ve Amygdaloidal andesite, overlying Orindan formation, Frowning Ridge ts cne | The Berkeley Hilts. Aa PALACHE If. Grizzly Peak andesite, porphyritic facies, southeast of Grizzly Peak, Analyst, Palache. III. Grizzly Peak andesite, holocrystalline facies, head of Telegraph Cafion. Analyst, Palache. IV. Summit of Grizzly Peak. Analyst, Palache. V. Aphanitic laminated andesite, Pie Knob. Analyst, Palache. VI. Aphanitic laminated andesite, Pie Knob.. Analyst, Dickerman. In the rock whose composition is given in VI, there is about 6.12 per cent of free ferric oxide which as limonite occupies largely the open spaces in the rock, and probably has a source foreign to the rock itself. In the analyses given, this 6.12 per cent ferric oxide has been deducted and due correction made. The rock analyzed is otherwise fresh. THE BASALTS. The basaltic lavas are scarcely subordinate to the andesitic in this field. They occur in both Upper and Lower Berkeleyan and in the Campan as important contributions to the accumulations which make up those series. They are found also to a small extent in dyke form. Although they occur, as the andesites do, at many different horizons, and have in the aggregate about the same volume and lateral extent, they are much more uniform in character and exhibit but slight variations in structure and mineralogical composition. Constituent Minerals.—Mineralogically the basalts consist essen- tially of plagioclase augite and olivine, with accessory apatite and magnetite. Glassy matter is present in some lavas. Serpentine and iddingsite are the most important secondary products, The feldspar is in two generations. The porphyritic crystals are sometimes sharply idiomorphic, more generally with indistinct and irregular outline or rounded and embayed by magmatic corro- sion. Twins formed on the albite plan are numerous, and Carlsbad and pericline twins are infrequently seen. Extinction angles meas- ured on albite twins which extinguished symmetrically, were as large as 36% degrees, indicating that the feldspar has the composition of bytownite or anorthite. Zonal forms are common, but less so than in the feldspars of the andesites. The smaller phenocrysts of feld- spar are usually quite free from inclusions; the larger ones, which 428 University of California. [VoL. 2. sometimes attain a size of one half an inch in greatest dimension, are characterized by abundant inclusions of augite, magnetite, glass, and serpentine. These have the same mode of arrangement and the same net-like aspect as was described in the case of the andesites, but here even more abundant than as there described. The feldspars frequently exhibit irregular cracks, which, as well as the cleavage cracks, are filled with pale yellow serpentine. Alteration seems scarcely to have begun in this mineral, which seems to be the most stable constituent, appearing fresh and glassy in the most rotten specimens of the rock. The feldspars of the ground-mass are both microlitic and granular in habit, more com- monly the former. They are, apparently, quite basic in composi- tion, their extinction angles indicating labradorite. Twins are the rule in even the minutest microlites. The microlites sink to almost sub-microscopic dimensions, and on the other hand by increase of size, merge with the porphyritic crystals. Augite, like feldspar, is in two generations. Phenocrysts of this mineral are almost universally present and generally exhibit sharp idiomorphic boundaries with characteristic form and cleav- age. The mineral is colorless to pale fawn color, non-pleochroic, with extinction angle cAe as large as forty degrees. Twins of normal structure are common, and zoned crystals were observed, which gave undulatory extinction. In certain very local forms augite was observed forming ophitic intergrowths with feldspar, the irregular angular areas of augite between the feldspar laths having the same optical orientation over considerable spaces. As a constituent of the ground-mass augite is invariably in small rounded granules, filling interstices between the feldspar individ- uals, and, apparently, the last product of crystallization of the magma. Alteration of augite appears to be usually to a yellowish serpentine, rarely to chlorite, and has taken place extensively especially in the augite grains of the inclusions and the ground- mass. The calcite observed in the slides is probably due to lime set free from the augite by this decomposition. Olivine is abundant in most specimens of basalt, and is prob- ably present in all, though not always observed. It is always in porphyritic crystals sometimes of large size and of characteristic an ece | The Berkeley Hilts. 429 idiomorphic form. These crystals are much rounded and embayed by magmatic corrosion, and fractured by mechanical strains. Its relations to the other porphyritic constituents show it to be the oldest secretion from the magma. The olivine is colorless and non-pleochroic, with high relief, and strong double refraction. Imperfect cleavage is indicated parallel to the pinacoids, the parting parallel to the base being the most pronounced. The alteration of olivine to serpentine may be studied in all stages of development. It usually takes place along the nearly rectangular cleavage cracks, along irregular curved cracks, generally present in the crystals, or from the periphery of the crystal alone. The serpentine is for the most part structureless, rarely showing a fibrous character, the fibers at right angles to the surface of decomposition. As alteration extends away from the cracks, the olivine substance is generally divided up into isolated grains or “eyes,” occupying the center of a serpentine meshwork, and the ultimate product is a serpentine pseudomorph, characterized by this mesh structure. An exceptional mode of serpentinization was observed in one large crystal of olivine. Alteration had begun at very numerous points within the crystal and developed radially from them. No definite arrangements of these points could be detected, though the effect was that of an imperfect rectangular system. The round spots of serpentine are connected by a system of extremely fine curving cracks, each filled with serpentine; and in some parts several adjacent spots have coalesced, forming a band of a second- ary mineral. The aspect of the crystal thus affected was very similar to that of the feldspar phenocrysts, with net-like arrange- ment of augite or serpentine inclusions described elsewhere. Olivine also appears to aiter to a laminated yellowish mineral, with characters which ally it to iddingsite. Magnetite is invariably present in the basalts as large aggregate grains and in small sharply-bounded crystals, and elongated, rod- like individuals. In one phase of the rock the sharp octahedral crystals are in part scattered singly through the ground-mass, in part grouped in beautiful reticulated aggregates, the bars of the network formed by octahedrons placed point to point in parallel position and branching at definite angles. Zones of grayish sub- 430 University of California. Ona: stance like leucoxene surrounding many magnetite grains indicate that a portion, at least, of that mineral is titaniferous. Apatite is always present as inclusions in the other constitu- ents in the form of elongated colorless prisms with characteristic optical properties. The properties of the serpentine, which is so abundantly devel- oped in the basalts, are identical in all respects with those already described for the serpentine of the andesites. The secondary mineral which has been noticed in both basalt. and olivine-bearing andesite, is believed to be iddingsite. It is. quite abundant in forms of the basalt which exhibit the most alter-~ ation, but in fresher rocks it was seen in process of development from olivine. Macroscopically it is not very prominent, but may sometimes be seen asa bronzy or yellowish mineral with good cleavage. In thin sections it has a pale green to greenish or brown- ish yellow color, and either the characteristic hexagonal outline of olivine or a sharply rectangular form also seen in olivine crystals in the same slides. Its distinguishing features are a very dis- tinctly laminated or fibrous structure, the fibers parallel to the prismatic axis of the crystal; distinct pleochroism in shades of greenish yellow, the absorption greatest in the direction of the fibration; straight extinction; and strong double refraction, the mottled polarization colors showing bright green and crimson tints. An imperfect parting transverse to the prismatic axis was observed in a few crystals. Crystals showing these characters were seen still retaining unaltered cores of olivine, which is doubtless the parent mineral. No observations were obtained which established the orientation of the optical axis with reference to the cleavage of the mineral. In all observed properties it appears to agree with the mineral described* as iddingsite. If further study should demon- strate its identity with that mineral, it will be of interest as proving that iddingsite may be formed by alteration of olivine, as previously suggested but not confirmed. *“ Geology of Carmelo Bay,” Bull. Dept. Geol. Univ. of Cal., Vol. I, No. 1, Ds 32, ,euseq- Eruptive Rocks of Point Bonita, /é7d., Vol. I, No. 3, p. go. eal The Berkeley Ftilts. 431 Chlorite is sparingly present in some sections of the basalt as an aggregate of pale green color, weak pleochroism and weak double refraction. Varietics—The basalts show structural variations, depending chiefly on the degree of development of crystallization and the corresponding coarseness of grain of the rock. Such variations are local in character, and the same flow may exhibit many of them within a very small area The most typical form of the basalt, characteristic of the flows 1eposing on the Siestan formation, is a very fresh-looking dark iron- 2zray rock, compact and massive, with a fracture varying from even to splintery and uneven. It is distinctly porphyritic, crystals of glassy feldspar, with striated faces, and yellow grains of olivine, the latter sometimes the more abundant and conspicuous, being readily distinguishable with the unaided eye. Pyroxene in well-cleaved plates is also sometimes visible. In thin sections this rock pre- sents the features of a typical doleritic basalt. Phenocrysts of feldspar, augite, and olivine are imbedded in a granular or micro- litic ground-mass consisting of feldspar, augite, and magnetite. In rare cases, a typical ophitic structure prevails, the lath-shaped feldspars forming an interlacing network filled in with large allo- triomorphic individuals of augite. The ground-mass often exhibits the effects of differential movements of the rock previous to con- solidation in the parallelism of the microlites or their tangential grouping about the phenocrysts. Scarcely less common than this form is an almost aphanitic facies found in portions of flows and the edges of the dykes. — It is deep iron black to reddish black in color, with even to subconchoi- dal fracture, and has a characteristic basaltic aspect. The texture is compact and is either perfectly aphanitic or uniformly and finely crystalline, with occasional crystals of porphyritic dimen- sions. In thin section these fine-grained basalts show a more or less uniform admixture of lath-shaped feldspars, grains of augite and magnetite, and small idiomorphic crystals of olivine, with gen- erally some glassy matter in the interstices. Flow lamination is more marked in the\ fine-grained forms of the porphyritic facies, and is often macroscopically visible in an irregular and imperfect lamellar parting parallel to the plane of bedding. 432 University of California. [VoL. 2. Vesicular or brecciated varieties of the basalt are rare. In the massive flows of the Upper Berkeleyan occasional white dots are visible, which in thin section are seen to be amygdules filled with opal and natrolite or calcite. In the basalt quarry above Pie Knob, where the basalt is seen resting upon gravel, portions of which it has picked up as it flowed along, were found fragments of highly scoriaceous lava, presenting unaltered the aspect of the vesicular scoria which accompany modern lava flows. But at no other point were forms of this character found, and they are undoubtedly exceptional. The large dyke which cuts the gravels north of Orinda Hill exhibits an interesting variety of structural features. On the edges of the mass the rock is fine grained to aphanitic in texture, dark gray in color, and distinctly laminated. The structure changes rapidly as the distance from the edge increases, till the rock assumes a distinctly granular aspect, with a rough fracture and reddish gray color. In thin section the coarse-grained rock is seen to possess hypidiomorphic granular structure, the idio- morphic feldspar and olivine being surrounded by allotriomorphic augite, and little or no ground-mass present. Here are found the beautiful reticulated aggregates of magnetite described above. In this, the most coarsely crystalline rock found in the area, was found a structure the nature of which is problematical. At irregular intervals small spherical amygdules of calcite occur. In a section cut through one of these there was seen to be, in addition to the filling of granular calcite, a narrow band of dark semicrystal- line material intervening on one side of the space between the cal- cite and the normal rock substance. Further examination revealed other areas of a similar material not associated with amygdaloidal fillings, but forming dark-colored, sharply-defined oval spots about a quarter of an inch across, in the mass of the rock. These spots are scarcely visible in the hand specimen, but in thin section they stand out prominently from the surrounding coarsely crystallized material. They exhibit thin, lath-shaped feldspars, and augite grains contained in a brownish glass full of minute microlites of feldspar and magnetite. Minute areas of calcite and serpentine replace portions of the ground-mass. None of the constituents of —— Picco The Berkeley Fills, 433 these spots show any definite position with reference to the bound- aries of the area, but the lath-shaped crystals of the surrounding rock are arranged tangentially to the oval space, as might be the case in an ordinary vesicle. In short, these spaces. seem to be occupied by portions of the magma in which crystallization was checked suddenly at an early stage of development by a cause which did not affect the mass of the rock. Observations were not sufficiently numerous to show whether the occurrence of amyg- dules with these areas was accidental or otherwise. Their pres- ence may indicate that the disturbing cause which affected crystal- lization was of a gaseous nature, but this is not certain. They may possibly be variolitic in nature. Whatever their cause, it must have been of an extremely local character, its influence not extending further than a fraction of an inch. Chemical Characters. From the above description it is clear that the rocks of this group form a well-defined and closely-related series with the structural and mineralogical composition of olivine- basalt, and dolerite. The chernical composition, so far as known, is in agreement with these conclusions. But two complete analyses of the basalts have been made, one specimen selected being from the flow above the Siestan formation, the other a characteristic basalt from the Campan. Silica determinations were made, how- ever, of other basalts of the series, and the results are pre- sented in the accompanying table. The percentage of silica in these several specimens is very uniform, the extreme range being little more than 3 per cent. The composition as a whole is that of normal basalt. It is interesting to note the close parallelism be- tween these analyses and those of the andesites already given. For comparison, the average of the first three analyses on page 426 is given in column VI. The differences are such as the mineralogical characters of the rocks would lead us to expect, the more basic feldspars and larger olivine content of the basalt being expressed in the lower percentage of silica, and the marked increase of lime and magnesia. The basalts approach very nearly in composition to the dolerite basalts of Etna as shown by the analysis quoted by Iddings.* * Origin of Igneous Rocks, Table V, p. 207. 434 University of California. [Vou. 2. Analyses of Basatts. I: i. III. IV. V. VI. Si Op....-. 48.03 50.77 48.10 47.61 47.86 58.76 it Opens « trace $28 | "svas can Pessdlessseescecaccetel troseeeceomeetes trace Al, O 21.81 TQ5AO” || View scsteesieva|ineseceiecs -cvaeeltueesceactaetes 19.40 Fe,0 3 2.25 A-A3 7 | ciseinrinsie ne vell i vonnts satclasenies ltbaastetien Peemeee 1.43 ETO: 6.04 B59 |i esceteesciccs|\aenccurscseuslace| teaasseceneteene 4.09 Mn O WSK | Ropecrencetounnibonna|| (SsbaEeetiaecn| | Gocepacco< ace. | aspEedaanee ooce trace CalO v3 9.15 QsSEy il Batoetavcceulllocsecvageseeeellascaseee meee 5-44 Mg O 6.11 Hi25 Billi ssescucessaelecccwenveaceeees 3-55 Na, O..... 4.58 DEOA | JV) recevetcuce esis eseuaanet: |teseo eee eee 4.38 Ken One 44 230; sill asssaanati st] eecdeecqeetteesd| Mine Seecteeeees 1.10 PouOgescess 33 SUSU OA ee eeiescll taeearezeeeae |e eee eee 25 1.30(@110° 18 @ eeere 2.16 { nore aacienien sian |iiseecaueesstnsatlisestesrsectettes 1.96 Motaless... 100.90 TOOS3ZO oe ee seotl| cancuazennecesalibecesnmen ce peeee 100.37 Sp. g 2.82 2.79 2.83 2.88 2.80 2.67 I. First basalt above Siestan formation { ml. S. E. of Grizzly Peak. Analyst, Palache. II. Basalt Quarry E. of Pie Knob. Summit of Bald Peak. Analyst, Palache. Te Analyst, Blasdale. IV. Basaltof Frowning Ridge escarpment beneath Grizzly Peak andesite. Analyst, Palache. V. Basalt of Frowning Ridge escarpment beneath first rhyolite tuff. Analyst, Palache. VI. Average of three analyses of andesite I, II, III. THE PYROCLASTIC ROCKS. See p. 426. The pyroclastic rocks of our field fall into two general classes, viz., (1) light-colored tuffs and agglomerates of rhyolitic composi- tion generally fairly free from ordinary detrital admixtures, and (2) darker-colored tuffs, generally decomposed and associated with or admixed with detrital material. The latter tuffs are basic in the sense that they contain no quartz fragments, but it is not clear in most cases whether they should be ascribed to basaltic or to ande- sitic eruptions. The rhyolitic tuffs are found chiefly in the Lower Berkeleyan and in the Campan basins, while the more basic tuffs occur at more numerous horizons in both Upper and Lower Berke- leyan and in the Campan. A few words of description are here given of these two classes of tuffs to supplement what was said of them in speaking of their field occurrence. Pecan The Berkeley Fills. Aas Rhyolitic Tuffs and Agglomerates.—In the conglomerates and tuffs which constitute the third stratigraphic member of the Lower Berkeleyan, the most important beds on the Frowning Ridge escarpment are whitish tuffs of rhyolitic material. They are more or less distinctly stratified, and weather with rough and pitted sur- faces, owing to the heterogeneity of the material. The acid char- acter of the rock may be recognized in hand specimens from the numerous fragments of quartz which appear in it, this mineral, together with feldspar, being large enough for easy identification. Under the microscope it is clearly seen to be fragmental, the larger component grains being angular or rounded fragments of quartz and feldspar, and occasional rock fragments mostly of a basic character. These are imbedded in a cement of varying com- position; glass is usually more or less abundant in shreds and wisps of white or yellowish color; kaolin or a cloudy kaolin-like substance is common, and there is always a certain amount. of chalcedony, in some cases so abundant as to replace all the other constituents. Grains of magnetite, hydrous iron oxide, and ocher- ous serpentine occur irregularly in the interstices, together with undeterminable opaque matter. Both orthoclase and plagioclase feldspars are present in fresh and water-clear crystal fragments; these and the quartzes are frequently rounded and embayed as if by magmatic corrosion, a process which could only have taken place before they were ejected and deposited in the present rock. Such rock fragments as were determinable were of the andesitic char- acter. The chalcedony forms characteristic radial aggregates showing the black extinction cross in parallel polarized light. It occasionally forms compact veins and bunches of greenish color flinty aspect. A thick lens of very similar rhyolite tuff occurs at a very differ- ent horizon in the Campan series in the tuff belt to the northwest of the basalt quarry, and the description just given would apply to it as well as to that of the Lower Berkeleyan. The tuffs and agglomerates which form the highest member of the Campan series differ from the tuffs just described chiefly in the coarser character of the fragments of which they are composed. In addition to the fragments of quartz and feldspar there are 430 University of California. [Vol. 2, angular fragments of rock several inches in diameter imbedded in a fine paste. This ground-mass, while of the same general char- acter as that of the rocks described, is more heterogeneous, and the finely comminuted rock and crystal fragments are more sharply angular. It, moreover, presents no evidence of lamination due to sedimentary deposition, as do the lower rhyolite tuffs. Mineralog- ically, however, it is much the same, exhibiting glass and kaolin with more or less chalcedony, in which are imbedded crystal frag- ments of quartz, orthoclase, and plagioclase, and fragments of rocks, both acid and basic, the former, of course, greatly preponderating. The larger fragments of the agglomerate which have been alluded to as weathering out prominently on the surface appear to fall into two classes. The greater number are hard silicious porphyries, white, gray, or green in color, with compact texture and even fracture. Exam- ined in thin section they are seen to be typical microgranites; abun- dant phenocrysts of quartz, orthoclase, and plagioclase, more or less idiomorphic, but much rounded and embayed by corrosion of the magma, and occasional crystals of brown hornblende and _ bio- tite; a ground-mass of microgranular quartz and feldspar, sometimes showing beautiful granophyric intergrowths, and inclusions in the phenocrysts of sharply idiomorphic crystals of magnetite, apatite, and zircon, and of gas and liquid inclusions in the form of negative crystals. The minerals constituting these fragments are identical with those found as more or less broken crystals in the finer por- tions of the tuffs. There can scarcely be a doubt that they repre- sent in massive form the magma from which the tuffs are derived. The other class of fragments embraces rocks of fine-grained por- phyritic texture, green to greenish gray in color, the weathered surface of which is black and pitted by the removal of needle- shaped phenocrysts. In thin section it has the appearance of an altered quartz-andesite. Lath-shaped phenocrysts of plagioclase, occasional corroded crystals of quartz, which may possibly be inclusions, and lath-shaped crystals of fibrous hornblende, are im- bedded in a microlitic base of feldspar, magnetite, and glass, colored light green by disseminated particles of uralite and chlo- rite. This rock is unlike any forms of andesite found in the Hien The Berkeley Fills. 437 volcanic series, in the presence of both quartz and hornblende. The latter, which is uralitic, is probably secondary, and may be derived from augite, but as this process has not been observed in any of the earlier volcanic rocks, even in fragments included in this same tuff, its presence appears to indicate a different origin for the containing rocks. A specimen of the finer-grained portion of the tuff was found to contain 68.8 per cent of silica. This indicates that the compo- sition of the tuffs as a whole agrees with that of the acid inclusions (microgranite) described above. The Basic Tuffs —Owing to their decomposed and altered char- acter, but little results from a microscopic examination of the more basic and dark-colored tuffs. In general it may be said that the volcanic fragments, in so far as they have been examined, appear to be andesitic, some glassy, and others holocrystalline. In the fresher specimens, such as are naturally selected for examination, such andesitic fragments, together with crystals and crystal frag- ments of plagioclase and augite, are imbedded in a very fine- grained matrix, which is commonly so obscured by the products of oxidation that little can be made of it. When this oxidation is advanced, the tuff may be of a red color, and, in the finer-grained varieties, it is then difficult to distinguish it from the lateritic surfaces of the lavas, or the ancient muds arising from the wash of such laterite. CHES SEOUENCE OR LAVAS. The volcanic rocks of the Upper and Lower Berkeleyan and Campan series comprise both lava flows and pyroclastic formations. Of these pyroclastic formations the rhyolitic tuffs and agglomer- ates stand out prominently in contrast to the more basic rocks with which they are intercalated. There are, moreover, no rhyolite lavas in our field with which they may be correlated. The more basic tuffs, on the other hand, seem to be referable to the andesitic and basaltic lavas, with which they are associated, except for certain thin tuff beds low down in the Orindan formation on San Pablo Creek, and similar tuffs in the Siestan formation, for which we have no known corresponding lavas. If we omit these basic 438 University of Calipornia, [Vot. 2. tuffs and make a complete list of the andesite and basalt lavas and rhyolite tuffs in the order of their occurrence, from the amygda- loidal andesite reposing upon the Orindan gravels to the rhyolite agglomerate at the summit of the Campan, we discover a very remarkable periodicity in the sequence. List of Lavas and Rhyolite Tuffs in the Berkeleyan and Campan Series in Ascending Order of Occurrence, Showing Periodicity of Sequence. Andesite, amygdaloidal. Basalt, thin flow in tuffs not separately mapped. rig Rhyolite tuff. Lower ( Andesite, outcropping only on San Pablo escarpment. Berkeleyan. 4 Basalt, thick flows. Dr: ( Rhyolite tuff, thin. y, (Deformation and erosion. ) Andesite, Grizzly Peak holocrystalline variety. re Basalt, subordinate flow not separately mapped. Rhyolite tuff, thin, superposition on basalt not certain. Upper Andesite, Grizzly Peak porphyritic variety. Berkeleyan (Siestan lake beds.) IV. Basalts, several flows. ? formations removed by erosion. (Deformation and erosion.) Basalt, andesitic. Campan. asalt, heavy flows. es site, several flows, with intervening lake beds. at tuff, thick, with other tuffs. Rhyolite agglomerate and tuff, summit of Campan. (Higher beds removed by erosion.) The tabulation clearly shows that in the entire succession there is a regularly-recurring sequence in the character of the erupted rocks. There are at least five such recurrences, or periods, and possibly six, if we separate period V into two parts. In four of the five periods the sequence is andesite, basalt, rhyolite. In period IV the rhyolite member is lacking, but may, have once Paracns | The Berkeley Hills, 430 existed, since all formations above the basalt in this period have been removed by erosion in the sections with which we are here concerned. In connection with this apparent defect in period IV it is worthy of note that to the north of Berkeley a sheet of soda rhyolite occurs, which has been described by the junior author of this paper.* This North Berkeley rhyolite is less than half a mile from the northwest corner of the area represented on the accom- panying geological map. It is known to be pre-Campan in age, and it is, therefore, entirely possible that it stratigraphically occu- pies the vacant place in period IV. In period V there is included a fivefold sequence. The first three members conform to the normal sequence of the first three periods. The remaining two members might be regarded as the upper two-thirds of a sixth period. , This remarkable periodicity may possibly be accidental. If a larger field were under consideration it might, perhaps, be found that rhyolite sometimes succeeded andesite instead of always fol- lowing basalt as it does in these five periods, or that andesite occasionally succeeded basalt instead of preceding it. If any gen- eral inference were to be based upon this sequence, that inference would be greatly weakened by these possibilities of accident and of error due to the limitations of the field of observation. The sequence is, however, not so employed. It is regarded merely as contributary data to the general question as to whether there is or is not any normal or natural succession of volcanic lavas. This general question has been before petrologists ever since the publi- cation of Richthofen’s classic memoir on a ‘“ Natural System of Volcanic Rocks,’+ and data have been gradually accumulated upon which an answer to the question will be eventually based. The sequence in the Berkeley Hills is, therefore, but a contribu- tary fact to the many which must be considered before a reliable scientific induction can be drawn. Whether it is an expression of a general law of succession of volcanic rocks or is due to local and special causes will depend on the extent to which it harmonizes with sequences worked out in numerous other localities. The *This Bull., Vol. I, No. 2. t+ Mem. Calif. Acad. Sci., Vol. I, p. 36. 440 University of Calfornia. [VoL. 2. sequence at present known, as worked out for example by Brogger* in the Christiania region, by Iddingst in the Yellowstone Park, by Geikiet for Great Britain, and more recently by Spurr§ in the Great Basin, are but partially harmonious, and it is evident that many more observations will be necessary in favorable locali- ties, where the fortuitous or accidental sequence can be discrimi- nated from the normal succession, before an acceptable general law, if there be any such law, can be formulated. The most satisfactory working hypothesis that has been advanced up to the present time is that announced by Iddings, || viz., that ‘the general succession is from a rock of average composition through less silicious and more silicious ones to rocks extremely low in silica and others extremely high in silica, that is, the series commences with a mean and ends with extremes.” Now the various periods of our local succession in the Berkeley Hills are clearly in harmony with this hypothesis, and to that extent support it. To the extent that they are harmonious, moreover, we have some measure of probability that the local sequence is an expression of the normal or general succession of volcanic rocks. It is to be noted, however, that in each of the periods of our sequence, there is an ¢zmediate passage from the andesite, or rock of intermediate composition, to the basalt, the most basic, without transitions, and similarly an immediate change from basalt to rhyo- lite. Moreover, the change is always from andesite to basalt and then to rhyolite. In this respect the succession is more definite and more clear cut than is implied in Idding’s hypothesis. Fur- ther, the periodicity or recurrence of the ternary sequence is more remarkable than the mere harmony of the periods with that hypoth- esis; and the periodicity minimizes the possibility that the har- mony might be a mere coincidence. 7 O72). G5., Vol. Lipp t5=35. +The Origin of Igneous Rocks, Bull. Phil. Soc. Wash., Vol. 12, p. 144. LO. j. G.S., Vol. XUVIM x892: ZJour. Geol., Vol. VIII, p. 621, 1goo. || Loc. cit. DAWSON] The Berkeley Hills. 441 PALACHE HISTORICAL, SUMMARY: The oldest rocks with which we are in this limited field con- cerned are those of the Franciscan series. These rocks are known to repose, in neighboring portions of the Coast Ranges, upon the worn surface of a granite, which is believed, for reasons which can not be entered upon here, to be probably of the same age as the post-Jurassic granites of the Sierra Nevada. This implies a post- Jurassic age for the series. The paleontological evidence as to the age of the Franciscan is rather scant, but its fossil foraminifera, molluscs and plants have been independently interpreted by differ- ent experts to indicate a place in the geological scale not older than the Lower Cretaceous. Before the recognition of the Fran- ciscan as a distinct series of rocks, the Knoxville had been regarded as the local base of the Cretaceous in California. But it now seems probable that the Cretaceous will have to be enlarged so as to embrace the Franciscan in its lower part. These Franciscan rocks, comprising a thick accumulation of sandstones, shales, foraminiferal limestones, radiolarian cherts, and volcanic flows, represent a long period of geological time and indicate numerous and important oscillations of level in the basin in which they were accumulating. They are, moreover, traversed very generally by basic intrusives, and with these intrusives are very frequently found irregular zones of contact metamorphism, The Franciscan was subjected to orogenic deformation and erosion prior to the subsidence which is represented by the Shasta- Chico series of marine sediments. The strata of this series are in the Strawberry Canon section not more than one-tenth as thick as they are in the northern part of the state, but the general character of the sediments is characteristic of the middle Coast Ranges and is significant of the conditions which prevailed during their accu- mulation. The Knoxville or basal division of the Shasta-Chico series is prevailingly composed of clay shale or sandy shale, with, in North Berkeley, some limestones, sandstones, and fine pebbly conglomerates. Avwce//a is found equally abundantly in shale, lime- stone, sandstone, and conglomerate. Belemnites occur in the sand- stones, and an ammonite, probably a species of /oplites, has been 442 University of California. [Vor. 2. found in the shales in addition to the awcelle. These beds rest indifferently upon the various formations of the Franciscan, and the latter afford many evidences of disturbance which have not affected the overlying Knoxville. Notwithstanding this fact, however, and the further fact that the Franciscan is made up of characteristic resistant rocks well adapted to yielding pebbles, no fragments of the Franciscan have as yet been found in the Shasta of this region. The radiolarian cherts and glaucophane schists of the Franciscan occur abundantly in the Tertiary conglomerates, and one would naturally expect to find them in the first over-lying unconformable beds. Their absence is in harmony with the generally fine-grained character of the Knoxville beds. These facts clearly indicate that the floor of the basin upon which the Knoxville sediments accu- mulated was a surface of exceedingly low relief, and that as it subsided beneath sea level there were no insular masses to afford beach material or high-grade streams contributing coarse detritus. If high land bordered the Knoxville sea, it was so distant from the middle Coast Ranges that the streams contributed practically only suspended matter to the accumulation. It is rare in stratig- raphy that such a fine-grained sediment as the Knoxville shales should be so extensively developed immediately above an uncon- formity, and it is not certain that in the middle Coast Ranges we fully understand the conditions which obtained during the accumu- lation of these strata. In the southern Coast Ranges conglomer- ates, with numerous pebbles of characteristic Franciscan rocks, occur, according to Fairbanks,* at the base of the Knoxville. Above the Knoxville and intervening between it and rocks referred to the Chico, is a stratum of rather coarse pebble conglom- erate. This conglomerate barely comes within the limits of our map at the head of Dwight Way, but is traceable for many miles along the front of the range to the southeast, in which direction the stratum increases in volume very noticeably. This formation is certainly significant of a very radical change in the conditions of deposition from those which prevailed in the immediately pre- ceding epoch. We may safely infer the deformation of the region to such an extent as to determine a much higher grade for streams *Jour. Geol., Sept.—Oct., 1898. Be cce| The Berkeley Fitts. 443 discharging into the existing sea, and at the same time a shoaling of the sea, inasmuch as conglomerates can only accumulate in water of very limited depth. Conglomerates are very commonly formed in broad sheets by the action of a sea encroaching upon a land area, the waves working over the fragments detached from the surface over which the sea is transgressing. This, however, can not be the explanation in the case of the conglomerates with which we are here concerned; for, although the conglomerate occurs characteristically at this horizon®* in the Coast Ranges, in extensive strata, yet the action of the sea upon the soft Knoxville shales could produce no such polygenous conglomerate as the one in question. The source of the conglomerates was, therefore, clearly beyond the limits occupied by the underlying shales. But the shales themselves were also derived from beyond these limits, and the change in the character of the materials supplied by the streams could only have been due to a sharp orogenic deformation which strongly accentuated the erosive and transporting power of the streams. This acute movement was followed by a long-continued, steady, and gentle subsidence of the sea bottom; for, resting upon these shallow-water conglomerates, is a great volume of sandstones with quite subordinate intercalations of shale. These comprise the Chico division of the Cretaceous. The sandstones are for the most part heavily bedded, indicating uniform conditions of deposition, and they are uniformly of medium fine grain. The entire record of Chico sedimentation is not revealed in our field, since the section of these rocks terminates at a surface of erosion. Nor is the attitude of the beds sufficiently exposed to indicate the degree of deformation to which the Chico had been subjected prior to this erosion. In the emergence into the zone of this erosion the region was very probably deformed, but this deformation does not seem to have been acute, since the strike of the beds is in general accord with the unconformably overlying strata. Reposing upon the erosion surface are beds of the Monterey Miocene, and it is from this fact chiefly that we know that it is an erosion surface; for, as has been already stated, rocks of Eocene * Cf. Diller and Stanton, Bull., G. S. A., Vol. 5, pp. 435-464. 444 University of California. [Vor. 2. age, which are abundantly represented in neighboring portions of the Coast Ranges, are here lacking. From this fact we may infer one of two things, either the region was uplifted at the close of the Chico, and this portion of it remained above sea level throughout Eocene time when the Martinez and Tejon were being deposited to a considerable thickness but a few miles away, or it was once covered by Eocene sediments, and these have since been removed in consequence of a post-Eocene uplift, together with some of the underlying Chico. The latter view of the case is the more proba- ble, in view of the proximity of Eocene sediments free from basal conglomerates, but it does not exclude the possibility of an earlier unconformity between the Chico and the Eocene. The Monterey strata, reposing upon this worn surface of Chico rocks, has a thickness of about 1,000 feet. The transgression of the sea, which permitted of this accumulation, must have been from the east toward the west; for, just to the east of the Berkeley Hills, in Contra Costa County, this particular formation of the Monterey series, characterized by cherts and shales, occurs resting upon still lower sandstones of Monterey age. It is here, again, difficult to understand how, under the normal conditions of trans- gression, such a formation, composed of cherts and very fine shales, with a minimum of terrigenous material in its composition, could be the local base of the series, unless the region undergoing subsidence were extremely flat, so that a slight depression should submerge extensive areas of the land. This consideration, coupled with the fact, above adduced, that the surface upon which the cherts and shales repose is an erosion surface, points unmistakably to the conclusion that prior to the Monterey subsidence a very thorough peneplanation of this portion of the region had been effected. The historical significance of the rhythm of sedimentation which so strongly characterizes the Monterey cherts and shales is not clear. Attention has been called elsewhere toa similar rhythm in the radiolarian cherts of the Franciscan; and it might be sup- posed that a comparison of the two formations, so similar in their composition and in their peculiarities of stratification, would lead to the discovery of some working hypothesis explanatory of the remarkable alternation of conditions which seems to have con- Lawson J The Berkeley Hills. 445 PALACHE trolled the accumulation of such rocks. It must be confessed, however, that no very satisfactory hypothesis has yet been formu- lated. Of course, various extreme possibilities occur to the mind, but we have little or no check upon them. For example, the rhythm might be due to an annual rotation of conditions. This would mean that each pair of layers in the series, one of chert and one of shale; is the result of one year’s accumulation. The average thickness of such pairs may be placed at three inches. This would mean that the entire 1,000 feet had accumulated in 4,000 years. This estimate shocks our current conceptions of the rate of accu- mulation of deposits which are chiefly non-detrital. It involves moreover a startling rate of abstraction of silica from sea water, whether the abstraction be effected by organic agencies or by direct chemical precipitation. If we assume that this particular basin in which the Coast Range bituminous shales were deposited had an area of 1,000x500 miles, the annual deposit would amount to about 100,000 mile-feet of silica in the form in which we now find it, which would be about 200 times, by rough estimate, the total amount of silica contributed annually to the ocean by all the rivers of the world. We have been unable to find figures for the proportion of silica contained in sea water, but the rate of abstrac- tion in this limited area is so much in excess of the supply to the entire ocean that the possibility of the rhythm being due to annual rotation of conditions seems to find little support in the computa- tion. Another possibility is that there may have been some rhythm in the swarming of silica-secreting organisms in the sea water. This, however, in the present state of our knowledge is pure conjecture and can not be regarded as a scientific hypothesis till we have some information which would support it. Still another possibility is that there may have been some rhythmical supply of silica from purely inorganic sources, such as submarine solfataric springs. The only fact that can be adduced in favor of this possibility is that in the lower part of the Mon- terey series in Southern California there is a great thickness of volcanic ashes, and that in some other portions of the series volcanic material forms a moderate but distinctly recognizable constituent in the bituminous shales. This, however, contributes 446 University of California. [Vou. 2. nothing to the probability of rytimical supply of silica from vents connected with this volcanic activity. It must be admitted, therefore, that we have not at present any reasonable working hypothesis explanatory of the rhythm of sedi- mentation of these remarkable strata. It may, however, be pointed out that the rhythm referred to is rather local in its development, since we have much greater volumes of the bituminous shales in other parts of the Coast Ranges in which such peculiar bedding is not apparent. The local development of the rhythmical sedimen- tation appears to be connected with the proximity of this portion of the basin to the land, and to be due to the rhythmical interrup- tion of a continuous deposition of silica by influxes of fine terrig- enous silts. If this be a fact, then the explanation of the rhythm in sedimentation must be sought for in the variation of the condi- tions on the surface of the land, whereby periods of discharge of fine sediments into the sea alternated with periods of !ittle or no discharge. Under such conditions the accumulation of silica, in the outer portions of the sea, removed from the seat of terrigenous deposition, would proceed uninterruptedly, and no rhythm would be apparent in the deposit. This consideration, it may be pointed out, favors the first possible explanation mentioned, viz., an annual rotation of conditions. But the problem is here regarded as an entirely open one, which invites earnest investigation. In portions of the Coast Ranges only a very few miles distant from the Berkeley Hills to the eastward there are several other formations of the Monterey series aggregating in volume 4,700 feet reposing upon this particular formation of chertsand shales. These higher formations undoubtedly originally covered the region of the Berkeley Hills, but were removed by erosion, after deformation, before the development of the basin in which the Lower Berke- leyan beds were deposited. We have, therefore, at the summit of this formation of cherts and shales an important hiatus in the history of sedimentation of the Coast Ranges. At the close of Monterey time orogenic movements affected this region in common with other portions of the Coast Ranges. The strata were folded, broken, and elevated above sea-level into the zone of erosion. After the Monterey rocks had been in places partly removed, PALACHE Bes | The Berkeley Fitlls. 447 together with still lower rocks, a subsidence ensued and the sea once more encroached over the Coast Ranges, and a new cycle of sedimentation was inaugurated for this region. This movement was accompanied by volcanic activity, for the next marine sedi- ments which we encounter in post Monterey time, those desig- nated the San Pablo formation, are in their lower part chiefly sandstones with admixtures of volcanic ash, and in their upper part almost purely pyroclastic sediments, some of which contain fossil shells. These beds of San Pablo age are lacking in the Berkeley Hills, though-well developed on the shores of the Bay of San Francisco a few miles to the northward. And it is there- fore believed that the San Pablo basin was one lying between insular or peninsular Jand masses, and that the region of the Berkeley Hills was one of those masses which remained unsub- merged in San Pablo time. Portions of the missing Monterey formation in the Berkeley Hills may, therefore, have been removed during this San Pablo epoch. Following the San Pablo, and in part during the latter part of the epoch, fresh-water basins were developed, probably in consequence of orogenic deformation. In one of these basins accumulated the deposits of the Orindan for- mation, which lies unconformably upon the rocks of Monterey age. That there was a close connection in time between the San Pablo and the fresh-water deposits of Orindan age is clearly shown from the fact that the pumiceous tuffs of the upper part of the San Pablo are also found in the basal part of the Orindan in the vicinity of Pinole. The Orindan in its full development is not less than 2,400 feet thick, and we seem to have in such an accumulation of fresh- water beds, chiefly lacustrine but probably also in part fluviatile, very clear evidence of depression of the region during their accu- mulation. That such depression was orogenic or local rather than epeirogenic seems also clear, since a general depression would undoubtedly have admitted the sea, and we find no trace of marine conditions in the basin, except to the southeast, where, to the west of Bollinger Canon, we find that the sea at the close of the Orindan, had access to the basin for a time, and marine conditions displaced the lacustrine. The marine beds attain a thickness of about 2,000 feet, and their fossil fauna is, in the opinion of Prof. J. C. Merriam, 448 University of California. [Vo. 2. closely allied to that of the San Pablo formation. These beds con- stitute the Trampan formation, so named from Las Trampas Creek, along which they are exposed. Their presence here, signifying the local displacement of the fresh water by the sea, is clearly indic- ative of orogenic deformation of the basin during the progress of its filling up. This marine encroachment did not apparently extend to the Berkeley Hills, for we find no trace of marine sedi- ments between the Orindan formation and the overlying volcanics. The accumulation of the Orindan and Trampan formations was brought to a close in the region of the present Berkeley Hills by the outburst of volcanic activity; lavas spread out over the floor of the basin; but the lake was re-established, for we find lacustrine deposits between some of the lavas, notably 30 feet of fossiliferous fresh-water limestone intercalated with the basalts of Eureka Peak. Finally, however, this lake was drained, or more probably dis- placed. The basin was then subjected to deformation, by which the strata were flexed and elevated. The erosion which followed had cut out important channels, when another set of lavas, the Grizzly Peak andesite, occupied these channels and also spread out over the earlier lavas. In the channels we find the lavas of the second epoch, Upper Berkeleyan, are reposing upon the worn upturned strata of the lake beds. The occupation of the drainage channels by these Grizzly Peak andesites re-established lacustrine conditions, and the Siestan lake was the result. This lake became filled with a varied assortment of sediments to a depth of about 200 feet. Their fine character and general absence of delta material indicate that the lake had a somewhat prolonged existence. The lignitic character of some of the beds, the occurrence of fossil leaves in others and of well-preserved trunks of trees in others, points to abundant vegetation on the shores of the lake. The two well-defined beds of limestone gen- erally free from detrital admixtures, and having a thickness of from 10 to 20 feet, with other thinner beds of less importance, contribute to the idea of long duration for the lake. They also afford a picture of clear waters comparatively free from sediment during their accumulation. They, moreover, indicate a non-organic source for the carbonate of lime of which they are composed. Boieae|| The Berkeley Fitts. 449 The occasional thin beds of volcanic tuff found intercalated with the clays and shales in the Siestan basin, tell us of the spas- modic sputtering of a volcano in the region, but too distant or too inactive to pour its lavas into the lake. Eventually, however, this volcanic energy burst forth in floods of basalt, which destroyed the lake and occupied its basin. Between these flows there were considerable intervals, as is shown by the oxidized surface of the lava and by the presence of tuff beds at the same horizon with thin beds of limestone deposited in a new sheet of water established on the surface of the first flows- To what extent these lavas piled up over the Siestan basin we can not now tell, for the surface at which they terminate upwards is one of erosion. The occupation of the Siestan basin by these lavas was fol- lowed, after an interval of unknown length, by the deformation by flexure of the entire region, and what remains of the Siestan lake beds and of the overlying lavas occupies the axis of the great synclinal trough. The establishment of this structure was followed by prolonged erosion, whereby the upturned edges of the folded strata were worn down and the corresponding anticlines entirely removed. Across the northwest end of what then remained of the syncline there was established the Campan basin, probably by a renewed deformation of the region. The earliest rocks to occupy this basin were clays and shales, with lenses of fresh-water limestone, sandstones, and conglomerates. These were followed by alterna- tions of lavas or tuffs and lake beds, the last of the series known to us being a rhyolitic tuff and agglomerate, of which the succeeding erosion has left only a few remnants capping the hill tops. In the midst of this Campan accumulation the basin was converted by the Canon fault into a structural trough, which the later lavas and tuffs filled up. After the Campan basin and trough was filled, it was syncli- nally folded and variously faulted, the faults apparently belonging to the same system of movements which in part gave rise in later time to the depression now occupied by the valley of the Bay of San Francisco. But before this valley was evolved, the region had 450 University of California. (Vor. 2. yet to undergo a most extraordinary history. The Merced series on the peninsula of San Francisco only a few miles distant is post- Campan in age. To permit of its accumulation, that portion of the region sank over a mile beneath sea level, and the trough so formed was filled to the brim with marine sediments of late Pliocene, and in their upper part of Pleistocene age. Then this trough was deformed, the floor upon which the Merced was laid down was lifted high above sea level,* the Merced beds were tilted at angles as high as 75 degrees, and were dislocated by a fault having a throw of not less than 7,000 feet.t After this we enter upon the cycle of ero- sion, vertical oscillations of the coast, and minor faulting, which has resulted in the modern geomorphy of the middle Coast Ranges. University of California, December, 1got. * Cf. this Bull., Vol. I, No. 4. +Cf. Sketch of the Geology of San Francisco Peninsula, U. S. G. S., 15th Ann. Rpt. PY. = a eee 2 OS eee aes | A A _ \ AFFLING GULCH SAV FABLO_ PRIDE ECREKA PEAK SIESTA VALLEY ><. SAN PABLO os VALLEY ( : Tt Hl Ae Sea Leve/ : FROWNING RIDGE ‘ HN Iii : alll Hn j \ WUT l | = i ih Hi | nny (il | | Cn ul enc Sea Leve/ | | Ml HI FROWNING RIDGE | Hl i ee SAN PABLO | i sacar" |\))/\/\())/)))))) oon : ‘ROWNING BAFFLING GULEH (Wild CatGrede WOLSEY CANON Win. ee : | : Hi ll ee a re | ! i Sea Leve/ SUN TABLO_ RIDGE Ih | tn Wild: Cat Gre Sea Level LEGEND LEGEND a Alluvium, eto. (re f aoe) Basalt Rhyolite tuff and agglomerate Conglomerate and tuff Basalt flows Tuff and Conglomerate Q__| with small lenses of lime- Basalt flows y stone and patches of basalt with intercalations of tuff = - and laterite : dositio Ba . id == 5| hy Andesitic Basalt Dolerita (intrusive) | Uv “Andesite to) io} i) | 3 0 Andesite ‘Tuffs Conglomerates and clays LSet aces Knob Amygdaloidal Andesite Andesite ORINDAN } E y : f f Sa eon | | FORMATION Z Sie 5) eel a : Hy) k AAA Conglomerates and Tuffs Fresh water conglomer- ates, sandstones, shales, lavas limestones and tuffs i 3 Bald Peak Basalt MONTEREY SERIES Miocene Bituminous shales and evenly bedded cherts with thin beds of sand- stone and limestone Tuff and laterite (e| U uel tu Se) Bi) rpentine Basalt UI e cS % = Basalt Aporhyolite 5 : tut » Fresh water lime- a ay stone SHASTA-CHICO. SERIES | SIESTAN Cretaceous Sandstones and shales 4 ‘ORMATION. Gb = | stones, shales, lige © | nites, clays, limestone 0 and chert, tu’ FRANCISCAN 0 SERIES 5 0 Sandstones, cherts, shales, schists, serpentine and other basic eruptives Grizzly E with subordinate flows of ‘asalt and intercala- tions of tuff \ Vey, a Ai fi Lith Bolton bey SP . Rhyolite tuff BNI sey oy Geological Map of a Portion of | THE BERKELEY HILLS By ANDREW C, LAWSON and CHARLES PALACHE | Scale wedc00 Contour Interval |0 feet. | 1900 | | INDEX TOL. VOLUME 2. Note.—Italicized page numbers indicate maps or illustrations. Page AGE of pre-granitic rocks of Pt. Reyes . . i32 BENDIRE, Capt., collections by AGUADULCE, formation. ...... . 234, 258 BERKELEY HILLs. AMYGDULES, of andesite ........ . 419 —, General section of . PRO ZONFBEEIS IF a ( cyiolie-js « i. vst seta ge sl Buty g00 —, Geological map of . ANACAPA .. . Rabe: ete. Meee LOS BERKELEVAN SERIES . . ANALCITE- DIABASE | Neteyiees anaire, ‘ora Spal Berrany, G. T., on Oredontida: ANALYSES: BEVELING, use of term . : BRE LC tte ti ge eis 6 ee ek wy ce 4S —, Considerations modifying ‘term . MAD GESIL@ ts. fog a ee wae, os we wl 5 ONG 20 , Hypotheses of ........ , 175 Soy Agee eh | a ne a ae ee EARS G31 BITUMINOUS SHALE . a ats ez 5,9, 365 — Augite. Ri raMec eRe Acca ny Pe te ease ME Oe SE — —, Chemical characterof. 2.1... ubasalt, §.. Ae eta een are et —-/of Pt. Reyes... ... 4. + « 137, 138 , Bituminous shale Runa Seis; F Fae) —'—, Organic’ remainsiin. . 5°. «.. = IT, 14 seerhornblende 5... . 4 fw. 1 338 = =: Origin Olseee ee on dae kee a a ee RTA. Ben arite: AN Rae see peat, alte nen eA O —i—,'PRetrography’ <6... Nh. s epe s §6O —, Coquimbite .. . she Mee ne rare aan 323 Thickness .. . 9 cin LU) Ce Lea lo BLANKINSHIP, ie A., cited on Farallones. . 142 SLO PSEGE o, sete. We wes le ne a my B43 BLUE MouNTAINS . . i 5 ne 7 EP mHIGITeralCite vvelicm ier shel ss ee) Ss ASL BOLLINGER Cajon, ostracoda ...... 95 SM MCLASDAL Hs. es sw i . 4. ++ +. . 31 | BONNEY, cited on serpentine and trocto- —, Gabbro . . died: . ef 3 287) Davipson, Geo., cited on Anacapa 7 2 Q5 —-—— , submerged ValleySt. ftake tn tee cea e203, DAvIs, W. M., cited on peneplains <4 156 ——-—, g! graded streams os 164 DEFORMATION of Berkeleyan and Campan 410 IDTABASE wc tiee ss) Geib hehe da ec eeeer eee —, dykes of . ie Sanne aomed is pasar OO; 70 GABBR Os iaeeet ty een ae 4, 40 PEOhe Pots Shea cin comer piers nay ¥! — — chemical characters’ PER erg ee Dies Ure) ——, microscopic petrography...... 48 DIASTROPHIC TROUGH, of Campan. .. . 400 DIFFERENTIAL EROSION. . » « £66, 767 Divipes in hard and soft rocks... . . . 170 DRAINAGE of Point Reyes ........ 148 DROWNED VALLEYS .......+.-+. . 224 —a——, (Mazatlative. un ects co © 1) «bey er eras 200, ——, Panama . bs neh iol ena ego eal al ed _ Santa Catalina . chase toy wa) 220 — Santa Rosa. 4 22.6 «20 -7-226 DUNITE P % 258; /03, 72 Fon. cited on Colorado Region Pg Ok ——w— Miocene climate . . eet OO Dynamic Hisrory of Point Reyes sere eeAG) DOVEES OL basalts, 2.60) we. ete jaseen 2 42 Ecunoips, value in geological work . . . 1¢9 ELEPHAS remains on Santa Rosa... . . 229 ELEVATED BEACHES ........ ; 8 SBURG BEDS. shenfe, eles BOO ENDOMORPHISM of _granite . ee Misa GLO. Eoce i Panama 3 wy es 1246. ERUuPTIVE ROCKS, in Franciscan . PAs p55 | ETCHED FiGures of hornblende... . . IIL FAIRBANKS, H. W., cited on bituminous shale .. . . 139, 140 —-—-, elevation of Coast Ranges . Me 228 — —-—, granite near San Luis Obispo . . 129 FARALLONE ISLANDS, geology . . 1 142 FAULT BRECCIA, Of Point Reyes Granite . 127 FAULTING of Campan . . 404 408 Fau.ts of Point Reyes. ........ 143 FELDSPATHIC LLERZOLITE ide Meee, eens 3, = SSAXONICE ET snes eee meats) er ae) ete O8 FIELD GEOLOGY, instruction In... .. 353 FILEXURES of Berkeley Hills © . 0 = = 396 FORAMINFERAL LIMESTONE ....... 355 — --; of Point Reyes. is. f 6 as a wx. = 1133 FossiLs, of Isthmus of Panama... . . 233 —, Acer. eerer. Sse teee ss Me 289, 309 sme, PERMIF CR xe oe Ue a al foc se Tae sy OG) — —, dimorphum . gcd seat ray =) udect wee sms 00 —, Acmea mitra . as eles ania eo eee cece LOO; = AO LOCHEKUS : Mustoas has Aes naw yece te ea eeee 75 — | Alnus) COFV AINA ss oe. fen) se 280) University of California. =, "COYPinoldeSse steams ——, serrulatafossilis ..... — tAncillariai% 4 ee ee a ahh rte ko) 0 . Ancylus . . Paes plGvo a 6 — Anodonta nultaliana . Ah By =, ANOMIAT a... be eee — ANTROMI AG.) Ape Oe wn AY QUG Ue ala, si eae re ———, whitneyis. ose). wee — Ly COmnee feo, 3 0 —, Asaphis multicostata . fore —, Asplenium subsimplex Peep i or —, Astrodapsts antiselli .... a LUPE AUS Ds, a 5: Ls ae ee — —, whitneyi —, Aucella . —--,plochtt ... —,Axinus biséctusin’. san ny eee —, Betula augustifolia .. . SRO LLELUD LN ee ene rim : : : » Candona candida. J. oe aoe my SOV ACHES Ms a) ce ac Oe eT aclecaenier Bes. , Cardita ventricosta. . . . , Cardium , ae =) Carpinus grandis . Suist eae —, Cevuhideni.=, . saaeeees —-—, californica .... ej ee oregonensis , Chomida Vine: ant Chlorostoma br unneum ars a) Prins ets Be —AIGUS «Aeon ays. oe ee S CINUTA, 21. we eye Ou , Clementia —) Clypeaster brewer Janus... . WiGOKOULGALLOSRU es, ae a ene =y — Crategus flavescens - aie == OREDLOUIG Ss 1c knee eles ae ia i NOSE ELS cs nay vi secncent eh cab tet — —, rugosa : Bea —, Cyelocypris californica een — ,xglobosa : IGP O Oto —, Gllichnaoregona ...... —, Ovpria subangulata . —, Cypr idopsis phocenica Ap —, Cypris procera . ae —, Cytherea Boers —-—,vespertina .. —, Dentalium Filth ——, Stramineum:>........ — —, substriatum. . Bra PE (7) 3) sa ee eae LEHNER, analysis by... . , 2 LEvy AND LAcRorx cited on actinolite. . - 330 LIMESTONE, ostracod . . at eh Oe LINDGREN cited on Merced Series . . . . 116 LLERZOLITE aes ta ~ . wR zo! Los ANGELES embayment Bate ict Ob oe ——, Embankments within ....... .223 Los CERRITOS... .. 2... Bese) es 224 Los CoRONADOS.... . + Well tts Sele O2! Loup Fork beds. . . 2 sp? coe OS LOWER SUBMARINE platform . APRs’ ©. 34 1 ;s) ——-—, Depressionsin ......... .198 ———! Ridges on . SS Mamet Ale oe, MACPHERSON cited onteschenites . ... . 37 MAGMATIC VARIATION. . . Pes) MAGNESIUM AND FELDSPAT HIC “Rocks . ee. M/F MARBLE OF PoINT REYES ........ «131 MARIATO FORMATION . . oa 0 So 2945265 Marsh, O. C., Explorations by ot tetteh tami Bees —,on geology ot John Day Basin .... . 275 MARTINEZ FORMATION. . . . 363 MASCAL FORMATION : 278, 279, 295, 305, j07 ——, Fossils... 2s) s.-3.< SE ac RIDy/ ——, Originof. .. Pos es cre ree (2) _-- ’ Stratigraphic relations . ae 306 MATTHEWS, W. D., on geology of John Day Basini jj, 2. el a aa 277, 296 McMAuon cited on rocks of Lizard \. 82 MELVILLE AND LINDGREN cited on minerals of, Knoxville: 2).0.es 3.) eee 24 MERCED.SERIES). . ssc vey sed ce A SO ——,Ageof... Niiers we RIG --, Relations toSan Pablo. |)... . . 15 — —) Sea-urchins ROP Alerts S es GG LG) — —, Subsidence. . 51 MERRIAM, J.C., cited ‘on fossils of Trampan 447 ——-—, Pliocene ostracoda ........ 93 METAMORPHIC SCGHISTS] Face Seto ase METAMORPHISM, contact on dykes . 20 MINERALS of andesite .......... - 412 — of Basalt® 144 Secs. eee arate Serer Ay — of Crystalline Schists: {0.6 eae - 345 MINERALS: a=) AL PeLING) sarees ied wp she ot oe == PATDICGL Pi, vai seth tice eres Bs 6 aYls ==; Altaite: 2s Gece: lets i alse) Las eS AAR col _ ar ee Rect Pre end os) co 22, 27, 418 ’ Anthophyllite . PET oe iP s oc 344 —, apatite A et terete ei | 24, 416, 430 — Apophyllite . Me Mich eret ie aa co SO GOL —=,, Arar onite’: iso cis. via en te eG —, Augite Pp ts. 31, “413, 414, 428 —, Barites os 0): BLO? a 6 » in 1 BIG —, Calcite .. Petes oh, on —, Chalcedony of amygdules . Perit se ol, —) Ghlorite. 4... RO aries) Hb5 CS, — Coquimbite. . RMR. ary, —,.Datolite (0%, 0). Gee ss hc ee eS 20 —* Miallaigee; fs e-page unm 50a; Dawe te ees Ae —, Epidote wo cest ob ay? 1G pe —, Hsmeralditel s: 3) 4 eas epee 2 ts G20) —, Gypsum... ere “1s 16, 316 —, Hornblende, green wel tahcay ciel keh es RR 263 —— —,chemical properties ....... 332 — — —) cohesional properties: . . . .. . 2-330 OE Index to Page ——-—,formulaof..'*'*... Ae peskt) ——-—, optical properties. ....... 329 eek comes DAIT ES. Nay ik. secre: 1a va at vist wecauhiel 40s 335 — — —, chemical properties sluceate Wed 337 — ——, formula es Rt Rennie Weta Oak Let tek GOCCUILENCE, jap e/iss\fetu.penren % sy veles 335 ——-—, optical properties .. 337 —, Hydromagnesite . yeahs 316 ——wEiypersthene. 2. 6 a6 5 6 Sara ps? 1 U5 —,Iddingsite ....... nig aes Somers 430 mee ATTLOTNI EG: i, cgccei lap a, esa Se ol hi eee GW PE LbG) —, Magnesite ...... eae ee 316 er VIASNCCICE) | cays) .c: cirsen se, ar Se sie weedtOs.A28 —, Natrolite of amygdules Gy tec near sate ttd 20) —, Olivene. ...-...4.- a aleh ate Wed Oy A28i = ’ Opal of amygdules . ; 4 420 —,Orthoclase) .. 6 sr ay ee wal edeate ay i aA! mm PECCOUEE cgi a. eras nas 2.6%, 3/06 MPA rIOCIASG: «a... + « SPAN Gs coe Pa! a egies S—wrrocnionite, ., . «+» » <).« oy Ieegeunel bey week SAO —,Serpentine ...... Minto oe 405, 428 Seva Sc NeW an Vathias sax ayes) bir wb f 341 —, Tremolite........ Ribe n Shes 25340! Sp LLGOMn shen cis Se ah es a Se ofl ae 319, 326 IMINO GEN Tics. Pre Ml ey ie es eh on See a Concater ERO —, Depression. ...... nace ge ewe nl 4O. 2220) Sa, LOU en ee c ae eee. eae DA —, of Contra Costa County Pe: Cpeoman hace Oy, —Omeoint REyeS:. . tos ae 4 se els ee. 152 — of Point Sal. ....... rie 4 —, Petropraphy ......- sel uke 10 —, Sea:urchins..... ST isohae oats Je ce GAG 110 —,Sediments ..... Seater k apie! S—APOAALE ss, 0) goes aces Au orto Pence 185 MIONEEREY. SERIES 6 6 6 6.) a's a 8s 134 ature HATEBORICLEY |. aus; a a oy 81s 363 — —, Conditions of deposition. . are 45 tS EGEOSIOMW ie. n mle) Sw wisi @) lee So's ee 446 ——; Faulting 2: 2. ea. steep vertu 2 308 a SH OSSIISMMalsg epee reali diel gy 4s) - Selah 365, 367 —-—, Geomorphic features. ........ 370 —-—,Limestones .. ...... win oy 0366 ——, Rhythm of deposition .... . . 365, 444 =e OANCStOMES atic vs eoPeai ei is; of S| We ya. 365, eM OETUCCULEM Lice aici bce thet? smelted! 0 cy voncs 368 Fr WIRTECK TOSS is, fin cs ce enty se. eS speek OG —-—, Unconformity at baseof -...... 363 Monr1}0, conglomerate... 25. . . . 294), 247 =~, Gill = Soe once ee eens aeee ESN LO Mount DIABLo, sea urchins IIr NEWCOMBE, C. F., collections by 101 NICARAGUA, coastal plain Ofs . 224... y 267 INORG ged tees meee << Atel a ech ae elo ‘62, 67 =—iGabbror >... £ .. Banus tr adtetais, eee uO 2 O77, Q@GEAN FLOOR, depth. . 6 66s es ss 197 OYIVENE-GABBRO 2... 4 fe ee 8 08%, 68 TIN OL ILC Bite sakse Beech sie suns cick cl (a, avons eth 2 63 I NOnte-SaDDIO messes) ss + ce 2035100) ORINDAN FORMATION ...... Bee, eGo ATL ——,Intrusives:. os. ae + + + 373, 398 —-—,Thickness....... a 373) —-—, Unconformity at base ........ 371 OROGENIC MOVEMENTS, effect on topography 171 OSBORNE BANK!) 20% .. aot oie) sf LOZ, 180; 202 OSCIEEATIONS) OF ‘COAST, «0 A8 \ s 120 Osmont, V. C., on thickness of John Day f + 298 OsTRACODA, Bollinger GAR OME yee con Sine 95 —, Pliocene .. oy a Bont? AS ALE 93, Z00 —, San Pablo Valley . Sy Reape gs, Memon cade 8 94 =, ’ Wildcat Ganonin WA Meco) ote vows, see 94, 05 Otis, Werle MealpiDy = faaact acre ; 352 OvVERWASH gravels of Point Reyes” 142 Volume 2. 455 Page Beary Ts SANK Ey is. is, et tens) 6s) co) aa ate) wl co 291 PALACHE, C., cited on Crossite ..... .330 ——-—Serpentine ........... 754 315 PANAMA fe. je le. oh <, c Be head) bt: eapehea 232 ——MODMaAtlOn. Wists ee tees |c > « 233) 274, 244 =i, ossils: ya a.je se 5 a es + 233 ela pioth owes Ara ahs la hen, ara Ae oe —, Middle Pleistocene uplift. ....... 261 —, Modern stream gravels ....... . 264 . Oldest TOCKS/ 2. a. =: Riel sce ae im Lea _— — Origin of stream courses... . . as) e205) —, Pleistocene formations ........ . 257 —, Pleistocene peneplains ........ 257 —, Pre-Pliocene history .......... 249 —, Recent depression ........5.2.. 262 —, Tertiary peneplain.......... .2§2 —, Tertiary uplift ...... pe es laa aire 55 —, Tilting of Isthmus ..... F 251 = JOPOSTADAY sa 6 es os = APKy 23%y 25E —, Volcanic Complex .. 1... . se oo 245 TVARA TAR DAW See clu reve os, 16) ay eu aiaes osm) eee 236 —, Formation... Sree cetiaeiiy Peer 20% Peneplain, definition of edema) a SO —= Limitationsiof term 1% . 6... =. 24 161 —, Necessary conditionsof ...... . 158 = Objections to theory of........ .157 = eOTy: Of tile cada italien cattae noel 5 Se 155 PERIDOTIMES A sf cea os) % a * 6: cei Se 2 595050350 —,Ageof.. Muck mma ye oe) -; Association. with gabbro . eet crete 207 05,77 —, Banded structure. . . a, i —, Compared with other peridotites A TS —, Distribution. ........... Pc Ie 89 —, Lenses of gabbro in. . fie PENCE PIL) PERIODICITY Of volcanic rocks... . . . 438 PETROGRAPHY of Andesites . ..... . . 411 Of Basaltsiy «a she ee. aa a0 Pie sahoel AQT IRIGRIM ER eae aikina «tosis - 55, 63 PIRSSON ciled on differentiation of rocks... 86 PLEISTOCENE . 6.0.00 es ee ee eH 67 =~, OLMRATIAMAN veh ius s es) a esier as! aw 257 —~oOf PointsReyesit 0 5 a0. @ 5 =e % . I41, 153 SO SCINACLOM Siu cay ay a, alec sien mr ai es . 265 BPO CENEW sg esdecguics, ir), (eis Sars aie cay Sree OG) —, depression. . anus ier wae Or 224), Pet) —, of Berkeley Eile tobainte. 6 oye Retr —,Sea-urchins ........ i etsy a ame 110 Point REYES GRANITE — —-—, Endomorphism.......... 128 ——-—, Petrography ........- Hes 124 — — —, Relations to other Massifs. . . a 12S Point REYES PENINSULA... . .. ~ 120; 723 ———, Geologicalliterature ...... L25 ma Graniter sb 05 sah dite sear ei rath telat 122 BOINRSAT nti racers on ee 2 —-~, Elevated beachesof.. |... ecBanea e —-—,Geology ......... ae oe’ | may MAD Sas, ce 5 densa gay gh bare a fy a eS g ——, Topography. ......:. 3 Post- EOoceENE earth movements ot ‘Panama. 264 Post-MIOCENE erosion .,...... a ege 7) Post-PLioCeNE elevation 273... .% = + fs 228 PRE-CRETACEOUS of John Day Basin. . 278, 279 PRE-GRANITIC crust of Coast Ranges . . . 130 —-—, of Point Reyes. ........... 152 PROTOLABIS*DEdS( 4, es ui «we Sud oem 306 PYROGLASTIC: rocks), 2c... irate: ke PYRONENITE) << 305.5. 5 & ets) 2 573085 725 956 QUARTZ-DIORITE. fia2 5 ape 2 a =, 025106) — Ot John Way yBaSinia ia @) a anes cs) ar270 QUARTZITE of Point Reyes. ....... . 131 QUATERNARY of John Day Basin 312 ——POCA-ULCHING) 104-5, yc. «ee eee See IIo 456 University of California. Page RADIOLARIAN) ChertS 1, = -1j-5e © 354 RAMMELSBERG cited on water of horn- blende . Pe ee Cae ae Sie KT. | RANSOME, F. L., cited on sRuctoige! basalt. 45 —— Serpentine isin neeeey 5 AKE FORMATION. 278, 279 205, 307, 310 ——,Age.. ‘ Fs ee eee ——, Basin of deposition a) as ke Pee cee — BeISteydiClatcih ss A ee te a a “311 =a Fossils. Sarr —-—, Stratigraphy .. aa eoue ey GS LO, RECENT SANDS of Point Reyes . hess . $142 RECENT SUBSIDENCE of Point Reyes. . . . I5I RELATIONS of Campan and Berkeleyan ~ . 409 REMOND cited on Merced Series. . . . . . 116 RHyOLitic FLows of John Day Series . 291, 294 — Turrs and Agglomerates. ..... . . 435 ——, of Berkeleyatus « POpOg raphy t-5 75 Pl ie ana 148 —, Valleys... . Pir te tm Ae SUBSIDENCE of Central. America . Pn peals zoy/ —, of MexicaniGoast, =). cane e207 SuccESSION of intrusive rocks ..... . 88 SYENITIC BATHOLITES, of Panama... . . 249 SYNCLINAL TROUGH of Siestan - 387, 388, 790 TANNER BANK >... .. . . 180, 181, 186; 202 TARR, R.S., on peneplains . . 155, 157, 158, 160 TEALL, J. J. H., cited on differentiation of rocks fe ik ahs nee Ss — = —‘gabbros? 8.0 Felipe, OS TEJON FORMATION . . U3 08' TERRACE FORMATIONS of Point Reyes. 141, 147 Tertiary, Basal conglomerate of Panama. 243 _—, Percentage method.? | (7.0 3 jesse eee —,-Red shaleof Panama .'..... .. > 24g —, Vancouver Island . . ..7. .) <) =) sea eeenOn TESCHENITES mee Sede ob 6 oc 5 —, Chemical characteristics. ...... 29 —, Historyioh? = 20 et ome) COS lnaex to Page —, Microscopic Petrography ....... 23 mvlinerali Composition <6. «9... = 33 — of Portugal , ar An eeted ate eete a ay , Petrographical relations rata Recah ee kt S Structure . ads Parte Feee. Peen re 24 TICHOLEPTUS BEDS ‘ 305 TILTING of topographic profiles : Aaiypt Torio LIMESTONE . rece or + 234, 239 ==— Fossils... . . waar - 239 TRAMPAN FORMATION . a F . 448 TRANSVERSE FAULT of Berkeley ‘Hills . 397 TROCTOLITE + 55» 63, 69 MEG TCISSIC’ oso ict a tg si cha ee 9 ee EN CISSOICG. & Hee Acute teams Bharat 55 TRUCKEE BEDS ... Steere See TRUNCATION of Summits . 176 Turrs of Berkeleyan 377; 395 Turner, H. W., cited on Granite Porphy ry.130 TOL DONtine e naae a gl oS io! cele es 75) UNCONFORMITY between Campan and Berk- eleyan .. Pe ee » 409 Upper SUBMARINE PLATFORM « 199, 200, 201 ———, Wave cut and built ; 202 VEGETATION, relation to erosion 173 VERAGUAS, Crystalline Series . 247 IMISIONDELILTS profile: 0. fe es a mw + LAO VOLCANIC ASH . 4, 16, 50 ——. of John Day series . - i . ce Apacens eso Volume 2. 457 Page —-—,of Miocene ... Sea tee ap teed — —, of Panama formation - 244, 245 ——, Petrography... Mato Feceche tye 7s — —, Recent, of John Day Basin . . 314 VOLCANICS of Campan : . 403 VOLCANIC ROCKS of Frowning ‘Ridge - 374 VOLCANIC VENT. acer iee . 402 WapswortTh, M. E., cited on sie pe . 75 WAVE action . . 209 WAVE and current built features’ Sw 219 WAVE-CutT TERRACES, discussed . 208, 210 — ——, Preservation oi een Page shee WaAymMiIRE, Lieutenant. ... . 27, WEHRLITE a 57, 58, 63, or WHITE GULCH, geologic ‘al section .. . Pe ys WHITNEY, cited on Point Reyes Peninsula , 121 WHITTENBURG HILL, geological section . . 136 — —, Topographic profile . . L446 WiLpcatr CANON, Ostracoda - 94, 95 WILLIAMS, G. H., cited on Serpentine. . . 77 WorTMAN, on division of John Day beds. 277, 295 —, Collections by . i) apes wae 7A Wricut, F., cited on hornblende... . 332 YATES, L. G., cited on rocks of Anacapa . 195 ZIRKEL, cited on Atrerine 7.7) =) a = «i 30 ——-—Analcite..........-.... 38 7 ea. < eu Py 4 THE BULLETIN OF THE DEPARTMENT OF GEOLOGY OF THE UNIVERSITY OF CALI: FORNIA is issued at irregular intervals in the form of separate papers or memoirs, each embodying the results of research by some competent investigator in geological science. It is designed to have these made up into volumes of from 400 to 500 pages. The price per volume is placed at $3.50, including postage. The papers composing the volumes will be sent to subscribers in separate covers as soon as issued. The separate numbers -may be purchased at the following prices from the University Librarian, J. C. Rowell, to whom remittances should be addressed :— No. I No. 2. No. 3. No. 4. No. 5. SaNOu. 6: No. 7. No. 8. No. 9. No. 10 No. II No. 12. No. 13. No, 14. No. .1 No. 2 No. «3: No. 4 No. 5. No. 6 No. 7 No. 8. No. 9. No. Io. No. 11. VOLUME I. . The Geology of Carmelo Bay, by Andrew C. Lawson, with chemical analy- ses and codperation in the-field, by Juan de la C. Posada } Price, 25¢ The Soda-Rhyolite North of Berkeley, by Charles Palache ; o- brIce, L0G The Eruptive Rocks of Point Bonita, by F. Leslie Ransome ; Price, 40c The Post-Pliocene Diastrophism of the Coast of Southern California, by Andrew C. Lawson : . Price. 40¢ The Lherzolite-Serpentine and Associated Rocks of the Potreo, San Francisco, by Charles Palache mn me On a Rock, from the Vicinity of Berkeley, ‘containing a New Soda Bice 466 Amphibole, by Charles Palache The Geology of Angel Island, by F. Leslie Ransome, ‘with a Note on the Radiolarian Chert from Angel Island and from Buri-buri Ridge, San Mateo County, California, by George Jennings Hinde 3 » “Pr.cey45¢ The Geomorphogeny of the Coast of Northern California, by Andrew C. Lawson : Price. 30c On Analcite Diabase from San Luis Obispo County, California, by Harold W. Fairbanks : bh . PEICe; 25C . On Lawsonite, a New Rock- forming Mineral from the Tiburon Peninsula, _ Marin County, California, by F. Leslie Ransome . ; Price, roc . Critical Periods in the History of the Earth, by Joseph Le Conte . Price, 20c On Malignite, a Family of Basic, Plutonic, Orthoclase Rocks, Rich in Alka- lies and Lime. Intrusive in the Coutchiching Schists of Poohbah Lake, by Andrew C. Lawson . : Price, 20c Sigmogomphius Le Contei, a New Castoroid Rodent, from the Pliocene, near Berkeley, by John C. Merriam : : Price, roc The Great Valley of California, a Criticism of the Theory of Isostasy, by F. Leslie Ransome. 4 P : : Price, 45¢ VOLUME II. . The Geology of Point Sal, By Harold W. Fairbanks . Price, 65¢ . On Some Pliocene Ostracoda from near Berkeley, by Frederick Chap- man. Price, Ice Note on Two Tertiary Faunas from the Rocks of the Southern Coast of Vancouver Island, by J. C. Merriam . Sit, Prices oe . The Distribution of the Neocene Sea-urchins of Middle California, and. Its Bearing on the Classification of the Neocene Formations, by John GS Merriam : ; ; Price, Ioc The Geology of Point. Reye es Peninsula, by F.M. Anderson. pL PErICew25G . Some Aspects of Erosion in Relation to the Theory of the Peneplain, by W. S. Tangier Smith : Price, 20c aplk Topographic Study of ‘the Islands of Southera Cali fornia, by W. S. Tangier Smith : Price, 40c The Geology of the Central Portion of the Isthmus of Panama, by Oscar H. Hershey : : Price, 30¢ A Contribution to the) @enlosy a the Ton Bay Bian by yan C. Merriam Price, 35¢ Mineralogical Notes, by Arthur S. Eakle 5 3 ‘ : Price, roc Contributions to the Mineralogy of California, by Walter C. Blasdale Price, 10¢c ® M STE ee } We it RW) in ir My i (ee ah sf ii * oI ih A yh? ie. Trini As ry