The tasmanian naturalist

THE TASMANIAN

NATURALIST

The Journal of the

Tasmanian Field Naturalists’ Club

CONTENTS.

(Each Author is solely responsible for the opinions and facts recorded in his
article. The Club merely places them on record.)

Page

Club Notes .. .. .. .. .. .. 1

Aboriginal Stone Implements 2

Outlines of Tasmanian Geology, Section 21, by A. N.

Lewis, M.C.? LL.M. .. .. .. .. .. 3

The Sea Elephant .. .. .. .. 16

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HOBART

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1926

The Tasmanian Field Naturalists’ Club.

The Tasmanian Museum, Hobart.

OFFICE-BEARERS, 1926-27.

Chairman:

DR. W. L. CROWTHER, D.S.O., M.B.

V ice-Chairman:

MR. A. N. LEWIS, M.C., LL.M.

Hon . Secretary:

MR. CLIVE LORD, F.L.S.

lion. Assistant Secretary:

MR. J. C. BREADEN.

Hon. Treasurer:

MR. G. B. DAVIES.

Committee:

MESSRS. L. RODWAY, C.M.G., G. L. PROPSTING, M. S. R. SHARLAND,
A. R. REID, NORMAN WALKER (with Chairman, etc., ex officio).

Hon. Lanternist:

MR. G. B. DAVIES.

Hon. Auditor:

MR. C. W. ROBERTS.

NOTE.—Members are requested to bring Specimens for Exhibition at
the Meetings, which are held in the Royal Society's rooms, The Tasmanian
Museum.

This Club was founded in 1904 to bring lovers of Nature together, and
widen the knowledge of Tasmanian Natural History.

Subscriptions are due on the 30th September, and are:—10/- Ordinary
Members, 2/6 Junior Members. This includes copy of the Club’s Journal.

%\)t ®a£maman JlaturaltSt

New Series—Vol. II., No. 2. March, 1927.

— -- '•'

Club Notes.

Mr. M. S. R. Sharland, who has taken a prominent part in
the activities of the Club for many years past, has secured an
appointment on the literary staff of the “Sydney Morning
Herald,” and has left Tasmania. At the last meeting of the
Club members took the opportunity of saying good-bye to Mr.
Sharland, and wishing him success in his future career. Mr.
Sharland was presented with a work on Natural History as a
small token of remembrance. The Club will feel the loss of this
able nature photographer, but N.S.W. will gain, and doubtless
Sydney ornithologists will welcome our late member among
their ranks.

*****

The 1927 Easter Camp is to be held at Adventure Bay. All
members who propose to attend the Camp are advised to com¬
municate with the Hon. Secretary as soon as possible.

*****

At the last meeting of the Club members had the pleasure
of meeting Mr. A. F. Bassett Hull, of Sydney.

*****

A matter which will need the attention of the Club in the
near future is the better protection of the black swan. At the
last meeting Mr. Basset Hull stressed the point that in certain
other States the black swan was totally protected, and since then
there has been a movement started on the East Coast to limit the
season, so it would appear that the Club might well gather in-
formation on the subject, and take action if necessary,

2

THE TASMANIAN NATURALIST.

Aboriginal Stone Implements.

Among the many interesting collections of the stone culture
of the Tasmanian natives few examples from the South-Western
area are to he found. The reasons are readily apparent when
attention is given to the surrounding circumstances.

In the first place the South-West is uninhabited, and the
rough nature of the Coast, together with the rugged, wind-swept
mountain barriers of the inland portion act as barriers to settle¬
ment, as well as preventing many from even casually visiting
this great area of our island home. In the past the dusky natives
wandered amidst the coastal plains and button-grass moors in
search of wallaby and kangaroo, or dived for shellfish around
the coast. The immense shell heaps at Bond Bay and Kelly
Basin, near the mouth of the Davey River, hear eloquent testi¬
mony to many an aboriginal feast in the ages of long ago. The
kitchen middens give up their proportion of stone implements,
but these are hut little different from the millions of quartzite
chips which cover the hill sides. The predominating formations
in this extensive track are quartzite and mica schist. Such rock
was totally unsuitable for secondary chipping, and readily
explains the absence of implements showing the degree of
workmanship which are a common feature of the camping
grounds in most other parts of the island, although the extreme
North-East is another area deficient in suitable stone for
secondary chipping.

There can be no doubt that the average stone implement of
the natives of the South-Western area was merely a quartzite
flake, although in certain instances attempts were made to secure
better material.

An interesting discovery was made on the shores of
Schooner Cove, Port Davey. Here there is a rocky outcrop
where the stone has taken on a semi chert-like character, and
the aborigines have attempted to quarry out cores in order to
fashion their implements from this rock. My own observations
in regard to this quarry were confirmed by Mr. P. B. Nye,
Government Geologist, whose attention I drew to this interesting
spot.

Although several aboriginal quarries are known in the
Eastern sector of the island, this is the first that I am aware of
that ha6 been recorded from among the Pre Cambrian rocks of
the South-West,

Clive Lord.

THE TASMANIAN NATURALIST

3

Outlines of Tasmanian Geology.

Section 20 (Continued).

Classification of Igneous Rocks.

We have seen that rock may cool from a magma in different
conditions with reference to the surface of the ground or its
distance from its own edge, and these give us different character¬
istics independent of the composition of the rock. We have also
seen that although magmas are originally of one type they may
differentiate into several series with differing composition. Our
classification depends primarily on mineral constituants, and
rocks with similar composition are grouped into a clan. Each
clan may have solidified at any depth, and so acquired character¬
istics due to rate of crystalization. We therefore have a cross
classification of each clan into the Plutonic, Hypabyssal and
Etrusive members of that clan.

Further classification depends on constituting minerals.

(a) Basic Rocks.

Gabbro Clan. — These rocks are the crystalized form of an
original or undifferentiated magma. The normal composition is
labradorite (or lime-soda felspar with predominating lime)
+ a pyroxine -f olivine. These rocks contain between 45 per
cent, and 52 per cent, of silica.

(i.) Normal group.—This consists of Gabbro as its
plutonic member, dolerite, the hypabyssal and
basalt the effusive, and includes most of the Tas¬
manian basalts.

(ii.) Olivine free gabbro, dolerite and basalt.—The first
mineral to form is the olivine, and the very first
signs of differentiation gives us this family, which
includes the Tasmanian dolerite (usually termed
diabase) and gabbro. Further slight differentia¬
tions give us:—

(iii.) Quartz gabbros, quartz dolerites and quartz basalts,
which have a somewhat higher proportion of silica
and show a trace of free silica (quartz).

(iv.) Norite, a plutonic rock with a somewhat higher
proportion of quartz.

(v.) A variety caused by differentiation of olivine to an
orthorhombic pyroxene gives us Hornblende
gabbro, enstatite dolerite and hypersthene basalt.

4

THE TASMANIAN NATURALIST.

With a complete differentiation we have a parting of the
rocks giving an ultra basic group, in which the olivine crystals
have sunk and enriched the lower layers, an intermediate group,
in which the sinking of the femic crystals has enriched the upper
layers in silica and an acid group in which the same processes
have been continued until it has resulted in the production of
free silica (quartz).

(b) Ultrabasic Rocks.

Peridotite Clan.—The composition of these is olivine -f- a
pyroxine, and the total proportion of silica is under 45 per cent.
The term limburgitic (or felsparless) is often applied to these
rocks, and they present the only considerable rock masses with¬
out felspar.

Peridotite (olivine -f* augite, diallage, amp hi hole or horn¬
blende) is the Plutonic type, Monchiquite (similar com¬
position) or Perknite (similar but with predominant pyroxene),
Picrite (olivine -f- augite), Alnoite (similar), and Dunite are
the hypabyssal types. Limburgite (augite and olivine) and
Metitite Basalt (augite, olivine and melitite) are the effusive
types. Peridotites are found among the oldest rocks of the
West Coast, and are important, as serpentine is often derived
from the weathering effect of surface agencies upon Perido¬
tites. Sometimes iron ores are differentiated amongst these
rocks.

(c) Intermediate Rocks .

We now turn to the other branch of differentiation. The
composition of all these rocks includes from 52 per cent, to 66
per cent, of silica. They may he classified according to whether
their predominant felspar is plagioclase or orthoclase.

(1) Diorite Clan.—This approximates nearest to the
Gabbro clan. The composition is a lime-soda felspar (oligoclase
to labradorite) + a little orthoclase (not more than one-third
the quantity of plagioclase) -f- hornblende. Biotite or augite
sometimes take the place of hornblende.

(i.) Normal type.—This gives us Diorite as the plutonic
rock, with porphyrite as the hypabyssal, and
andesites as the effusive equivalent.

(ii.) Biotite diorite—porphyrite—andesite are the rocks
in which biotite has taken the place of hornblende
and pyroxene diorite—porphyrite—andesite when
augite or another pyroxene is present.

THE TASMANIAN NATURALIST

5

(2) Syenite Clan.

(i.) Monzonite family.—This is half-way between the
diorites and syenites proper. In it orthoclase
appears almost equal to the plogioclase constituent.
Monzonite is the plutonic type, and trachy-andesite
is the hypabyssal and effusive type.

(ii.) Soda-Svenite family.—The composition of this
group is soda-orthoclase -f- less abundant
plagioclase -f- a soda silicate (aegirine, etc.). Soda
syenite is the plutonic member. Solvsbergite and
tinguaite are hypabyssal, and soda trachyte is the
effusive.

(iii.) Felspathoid-Syenite family.—The composition is
orthoclase + a felspathoid (nepheline, leucite,
sodalitc, etc.) + hornblende, augite or biotite.
Nepheline — leucite — sodalite syenites are the
plutonic, nepheline, etc., porphyry are hypabyssal,
and Pbonslite and Leucitophyre are the effusive.
A great number of members and sub-members of
these rocks are represented among the alkali rocks
of Port Cygnet—Woodbridge.

(iv.) Potash Syenite family.—This has orthoclase + a
trace of plagioclase + hornblende, augite or
biotite, and is represented by Syenite, Porphyry
and Trachyte as its plutonic, hypabyssal and
effusive members respectively. This may be termed
the normal group of the Syenite Clan.

(d) Acid Rocks .

Granite Clan.-—These have always a total of over 66 per
cent, silica, some of which is free. The presence of quartz is the
distinguishing mark. They thus represent the opposite extreme
of differentiation to the ultra basic rocks.

(i.) Granodiorite family.—Composed of predominant
lime bearing felspar (oligoclase or andesive) +
orthoclase in small quantities -f- biotite and some¬
times hornblende -j- quartz. Granodiorite is the
plutonic member, Quartz Porpliyrite the hypa¬
byssal, and Dacite the effusive.

(ii.) Adamellite family.—In which the plagroclase is
equalled, or nearly so, by the orthoclase. Muscovite
is common with the biotite. Adamellite, Aplite and
Toscanite are the plutonic, hypabyssal and effusive
types respectively.

6

THE TASMANIAN NATURALIST.

(iii.) Soda-granite family.—Composed of soda orthoclase
or anorthoclase -f- biotite -f- quartz. Soda granite
is plutonie quartz porphyry and Keratophyres are
bvpabyssal, and PanteUerite is effusive. The
Keratophyres are of special interest, as they are an
important factor in the great ore deposits of the
West Coast.

(iv.j Potash-Granite family.—This is the normal group of
the clan. The ordinary composition is Orthoclase,
with occasional plagioclase -f hiotite + quartz,
its members are Granite, Granite porphyry and
Rhyolite. It is one of the most common rocks of
the earth’s crust.

Within these families all igneous rocks may be grouped, and
each are sub-divided many times, there being descriptions of 614
igneous rocks in Daly’s text book. This fact illustrates the
difficulty of attempting any generalised classification, and text
books must be referred to for further details.

Section 21.

Sedimentary Rocks.

We have discussed the types of rocks which may be pro¬
duced by the erystalisation of a moltern magma, and now turn
to the second major division of rocks which are formed on the
surface of the crust from broken fragments of the crust or from
the action of surface agencies. These are “deposited” by some
physical agency, and are termed Sedimentary. As in the case of
Igneous rocks, the mode of formation gives us the primary classi¬
fication, but with sedimentary rocks the chemical composition
of the constituting minerals is not always important in classifica¬
tion of types, and is only used in some cases. The mode of
formation often devolves to the place of origin. This is the most
important factor in the formation of sedimentary rocks, and
largely governs their nature.

The existence of igneous rocks connotes the previous exist¬
ence of some sedimentary rocks into which or over which
igneous rocks have been forced. The original cooled shell of the
earth has now entirely disappeared, and the oldest known
rocks have been built up from still older rocks. These have been
intruded by igneous rocks during all geological ages, and the
sedimentary rocks consist of a mixture of fragments worn indis¬
criminately from all rocks older than their date of formation.

THE TASMANIAN NATURALIST.

They have at times accumulated to great depths—some beds
have a measured depth of from 20 to 30 miles, hut this is in-
festissimal when compared with the diametre of the earth.
Sedimentary rocks, generally speaking, have a less density than
igneous rocks, and they are only found in the outermost zone of
the globe’s crust.

Origins of Sedimentary Rocks.

We have seen that various agencies are continually at work
wearing away all land surfaces. The materials so removed can¬
not leave the surface of the earth, but are merely redistributed.
Most are carried away by runnels, streams and rivers, and are
dropped when the current slackens over the plains or * re carried
opt to sea. All the materials worn from the coasts art deposited
over the sea floor. Wind distributes dust, and volcanoes some¬
times scatter ashes and volcanic dust over the land. Also certain
physical agencies such as evaporation, and chemical agencies
such as precipitation are at work in certain localities to cause
the formation of peculiar sediments. Finally animal and plant
remains at times accumulate in such quantities that they build
a sedimentary rock entirely out of their remains. Sea shells and
tree trunks are the best examples of these.

These three most important modes of origin—from frag¬
ments of older rocks, from the action of chemical laws and from
the remains of living organisms, gives us our first division of
sedimentary rocks into Fragmental, Chemical and Organic de¬
posits. Each of these major headings may he further divided
according to the place of deposition into deposits in the open
sea, or in waters other than the open sea, such as estuaries, lakes
and rivers, or on the dry land. These deposits are termed
Marine, Aqueous and Aeolian respectively.

Deposition .

A "'sediment” includes all the constituants of the future
rock other than those injected or ejected through igneous action,
and it includes even some of these when they fall as fine particles.
The w r ord connotes small particles, although some of these are
on occasion several tons in weight, but all sedimentary rocks
lack the solid mass of interlocking crystal units that characterise
the igneous rocks. The constituting minerals of the latter are
intergrown, sedimentary rocks are cemented together.

Under similar conditions similar deposits are formed. These
conditions are similiarity both of the rocks from which the de¬
posits are derived and of the physical environment of the place
of deposition. Thus a change from a lagoon to an open beach
caused by an invasion of the sea would alter the nature of the

8

THE TASMANIAN NATURALIST.

deposit, so will a change in the sediment brought down by a
river when it has, say, worn away a bed of sandstone, and is now
wearing into an underlying bed of dolerite. Changes in condi¬
tions are always going on. A flood, melting of ice in summer,
even a strong wind, the level of the sea, rising or sinking of land,
presence or absence of vegetation, currents congenial to shell fish
life, a volcanic eruption, all have their effect on deposits.

All sediments are laid down in layers. Wind blows a little
more sand over a piece of country, a flood deposits an infest is-
simal layer of mud on the estuary bed. The resulting rock is
seen to be made up of thin layers, separatable from the one
above and below' like the leaves of a book. Each of these is
called a “’lamina.” They may be no thicker than paper or so
thick that each stratum consists of one lamina. They represent
the layer of rock formed at one time from a single deposition of
sediment. A ‘'stratum” consists of one or more laminal deposited
one on top of each other, without a change of condi¬
tions. Its nature and origin is the same throughout.
Each lamina is parallel, and the whole stratum has been
deposited in the course of one period of deposition. Each
stratum is distinguishable from the one above and below by some
characteristic indicating a slight change of condition, such as a
flood or a diminution in sediments, or an invasion of the sea or
sand, or the absence of traces of life, or a change in the forms.
All the strata laid down in one epoch of deposition, that is, from
the time that particular deposition of sediment began until it
definitely stopped, is termed a “bed” or “series” of sedimentary
rock. Only a total interruption of deposition terminates the
formation of a bed.

Sedimentary Rocks.

From their mode of origin it follows that the outstanding
characteristic of sedimentary rocks is that they occur in layers —
termed stratification. Sometimes these layers are formed with
great frequency, and so are very thin. The rock is then said to
be finely laminated. At other times they are very far apart, the
rock is said to be massively bedded. In extreme cases
it is difficult to see that it is stratified at all. Strata that are
laid down exactly on top of the one below r , and so are perfectly
parallel, are said to be “conformable” to the one below. If
some slight change of conditions has occurred since the strata
below w r as deposited, so there is a distinct break in the stratifica¬
tion, and the next layer is thus not perfectly parallel, it is said
to be disconformable. If this change of conditions is so con¬
siderable that the deposited layer has consolidated, and then
been weathered, or eroded so that valleys and ridges formed out
of its surface or folded, or otherwise altered before the next

THE TASMANIAN NATURALIST. 9

layer has deposited the t\vo strata, will be said to he unconform -
able.

Within each stratum the laminae may not he parallel to the
line of the stratum. This may be due to the materials being
eddied about in the water, or to have been deposited on a steep
slope, or to the surface having been disturbed during deposition,
and is termed “false bedding” or “current bedding.” This is
more usually found in sandstone than in other rocks, and is the
typical sandduite rock formation. In this case as the angle at
which wind driven sand will stand—the batter, in other words—
is 30 degrees, the cross bedding never exceeds an angle of 30
degrees to the strata. The laminae often appear to be tilted or
even folded, but if the strata are looked to, it will he observed
that they were originally horizontal, and are parallel to each
other, independent of the laminae. This point must be closely
watched when examining sedimentary rocks.

Sedimentary rocks frequently vary considerably within the
bed, and even within the stratum, such variations being due to
local changes of conditions. Thus, in a bed of sandstone, patches
of mud will often be found. These changes are even more
noticeable between strata. Marine deposits are notoriously
liable to frequent change. Often these changes occur in groups
through the strata of a bed.

When a bed of sedimentary rock is considered as a whole it
will be roughly in the form of a parallelogram, longer in one
direction than in the other. If it becomes tilted the angle of tilt
along its longer axis is termed the “dip,” and the angle of dip
may be measured. A line at right angles to the dip is termed
the “strike.” Most inclined rocks have a dip along the line of
strike, as well as a true dip. Dip can only be calculated when
the limits of the bed are known, and an isolated outcrop cannof
be relied on to give the correct angle. A change of dip indicates
a break in the continuity of the strata, either a change in deposi¬
tion or a subsequent fault.

Such is, in short, the nature of sedimentary rocks as a whole.
We must now turn to study the various types. Our classification,
as has been indicated, will be into (a) Fragmental, (b) Chemi¬
cal, (c) Organic, with a sub-division of each heading into (1)
Marine, (2) Aqueous, and (3) Aeolian. Further sub-divisions
will indicate different places of depositions within each of these
sub-headings and differences in modes of origin.

(a) Fragmental Rocks.

1. Marine deposits.

(^a) Boulder deposits.

10 THE TASMANIAN NATURALIST.

These are deposits of rocks, the average size of which is over
6 inches in diameter. They are the first to be dropped when the
current of a river slackens on reaching the sea or to be dropped
by the currents of the sea when moving from the land. They
are therefore essentially shallow water deposits. The size and
nature of the component boulders may he infinite.

(i.) Boulders.—The unsolidified form in which
these rocks are first deposited. The con¬
stituent units are usually perfectly round or
nearly so.

(ii.) Screes.—An unsolidified mass of large rock
fragments similar to boulders, but with angu¬
lar forms and sharp edges, indicating that
they had little or no wearing by water.

(iii.) Conglomerate.—The rock formed by the
solidification of a boulder deposit by some
cementing material, the majority of the con¬
stituting boulders or pebbles being of a
similar rock.

(iv.) Agglomerate.—Similar to conglomerate, but
with the constituting boulders consisting of a
variety of different rocks.

(v.) Breccia.—The rock formed by the solidifica¬
tion of a scree deposit by a cementing
material.

(vi.) Basal Conglomerate.—When a bare rock sur¬
face is being first acted upon by the sea its
upper layers are broken by erosion into
boulders. When sediments are deposited
these boulders of the original rock form a
basal conglomerate consisting of boulders
broken from the older rock, which is to he
seen below, cemented by newer sediments
which form the rock above. A basal con¬
glomerate usually is seen in the foundation
layers of any bed of sedimentary rock.

(vii.) Glacial Conglomerate.—This rock is formed
by the dropping of boulders off a melting ice
sheet or floating berg into the sediments being
deposited below. It can be distinguished by
the variety in size, nature and shape of the
boulders dropped, and by the fact that: many
can be seen to have been obviously dropped
into the sediments that enclose them.

THE TASMANIAN NATURALIST.

11

(b) Pebble deposits.

These are the next fragments to be dropped from the
slackening current. They vary from coarse sand to small
boulders, and finer material are frequently present.

(i.) Shingle.—The unsolidified form of these rocks
in which the component pebbles are some¬
what large.

(ii.) Gravel.—Similarly but with fine component
grains.

(iii.) Grits.—The solidified form of gravel deposits.
These merge downwards into sandstones.

(c) Sand deposits.

These are the next fragments to fall, and, like the proceed¬
ing forms, are essentially coastal or shallow water deposits.

(i.) Sand.—Grains of rock sufficient large to feel
rough to the touch.

(ii.) Sandstone.—The solidified form of sand de¬
posits. When sand is being deposited the
grains are sufficiently small to allow the in¬
fluence of difference of weight to permit
sorting of sands of different minerals. Thus
sandstone more usually consists of one pre¬
dominating mineral. Sandstone, strictly
speaking, consists of grains of quartz. If any
other mineral is predominant its name is
added to the rock, as felspathic sandstone,
micaceous sandstone, etc.

(d) Mud deposits.

These are the ultimate effect of the sorting process, and are
only laid down when the current has no power to hold them in
suspension. In marine deposits they indicate deposition in deep
water— over 100 fathoms.

(i.) Mud.—Deposits of fragments too fine to feel
rough to the touch.

(ii.) Clay.—Deposits in which fragments are so
fine that they unite in a mass impervious to •
water.

(iii.) Mudstone.—Solidified mud.

12

THE TASMANIAN NATURALIST.

(iv.) Shale. — Solidified clay. Clay and shale are
very seldom found as marine deposits. They
usually indicate laucustrine conditions.

(e) Abyssal deposits.

Very little sediment reaches the great ocean depths. In
places a little has been dredged up. This consists of minute
particles ol rocks and volcanic dust and dust blown from the
land. This type of rock is unimportant.

2. Aqueous deposits.

(a) Boulder deposits.

(i.) Boulders. — Such deposits can only exist where
a stream or river has been able to erode them
into shape over a fairly lengthy course.

(ii.) Screes. — These are the more usual deposits of
shorter streams and mountain torrents.

(iii.) River drifts. — The solidified form of the
above. They may be conglomerate or
brecciate, according to whether the con-
stituants are round or angular, and usually
indicates a Hood plain and the first deposits
in an estuary.

(iv.) Glacio-fluvatile deposits.—The rocks formed
from material brought down by glaciers and
carried over the surrounding country by
water from the melting ice. They are glacial
deposits more or less sorted into grades of
fineness.

I b I Pebble deposits.

Gravel—grits.

(c) Sand deposits.

Sand — sandstone.

(d) Mud deposits.

Mu d—c 1 a y—m u d stone — shale.

All these deposits are found in this group. They are formed
under the same conditions and present the same features as
those described in the previous group. One additional rock of
peculiar interest must be noted under (d ) Mud deposits. That is:

THE TASMANIAN NATURALIST.

13

(v.) Varved shale.—This is formed from mud
carried by a stream issuing from a glacier. In
summer much ice melts, and a thick layer of
mud is deposited where these beds are form¬
ing. In winter very little water escapes, and
the mud deposited is slight. \ bed of these
shales presents an extraordinary succession
of thin and thick layers—each often of
different colours.

3. Aeolian deposits.

(a) Boulder deposits.

The only forms such can exist in this class is as materials
dropped from glaciers.

(i.) Till.—Glacial moraines after the disappear¬
ance of the ice.

(ii.) Tiilite.—Solidified moraine rock.

(b) Sand deposits.

(i.) Sand dunes.—Sand blown by wind, and
usually piled into a succession of ridges.
These are only seen along the sea coast.

(ii.) Sand ridges.—Similar ridges formed in dry
areas.

(iii.) Dune rock.—Solidified sand dune.

(iv.) Raised beach.—Rock formed by the solidifica¬
tion of an ancient beach, and consisting of
sand, shells, driftwood, etc., now found in¬
land through recession of the sea or uplift of
the land.

(c) Dust deposits.

(i.) Loess.—Deposits of fine blown earth. These
may be in a very solid form.

(d) Volcanic deposits.

(i.) Volcanic dust.—Deposits of fine materials
ejected by volcanos and settled down over a
land surface.

(b),Chemical Rocks.

1, Marine deposits.

Probably no rocks of this class occur.

14

THE TASMANIAN NATURALIST.

2. Aqueous deposits.

(i.) Chlorides, Sulphates.—These occur through
evaporation in lakes or enclosed arms of the
sea, and produce salt deposits, and when in

sufficient quantities, rock salt.

•

(ii.) Borates.—These are rare. They occur with
(i.) above.

(iii.) Carbonates.—Similarly.

(iv.) Travertine.—A hot spring deposit consisting
chiefly of calcium carbonate.

(v.) Suiter.—Similar, hut consisting chiefly of
silica.

(vi.) Limestone.—Sometimes formed from preci¬
pitated calcium carbonate.

(vii.) Dolomite.—Similar, hut with magnesia.

(viii.) Iron Ores.—These are formed in hogs and
peety marshes from the action of bacteria on
decaying plant remains. Bog iron and iron
pans, such as are common under our Button-
grass plains, are examples.

3. Aeolean deposits.

Few rocks are formed chemically on the surface of the
ground. Some salt deposits may he included here. Also buck¬
shot gravel—fine round red grains of gravel coated with iron
gathered from percolating water and bacterial action on decay¬
ing vegetation.

(c) Organic Rocks .

1. Marine deposits.

(a) Shallow water deposits.

(i.) Shell hanks.—These often accumulate to
great depths.

(ii.) Limestone.—Some of our most important
beds (e.g., at Maria Island) are merely con¬
solidated shell banks.

(iii.) Coral rock.—This often forms immense beds.

THE TASMANIAN NATURALIST.

15

(b) Deep sea and abyssal deposits.

(i.) Ooze.—This covers the flow of the ocean at
depths too great for sediments to reach. It
consists of the hard portions of small and
microscopic organisms that live and die on
the ocean above. Foraminifera, radiolaria
diatons and certain molusca and algae are the
chief constituting organisms.

(ii.) Limestones.—Solidified ooze.

2. Aqueous deposits.

(i.) Lacustrine ooze.—The yellow mud in many of
our mountain lakes consists largely of the
remains of diatoms.

i

(ii.) Carbonaceous mud. — Mud in which plant re
mains are present in large quantities.

(iii.) Carbonaceous shale. — Solidified carbonaceous
mud.

(iv.) Peet. — A mass of plant remains, formed
usually in hogs.

(v.) Coal. — A carbonaceous deposit formed from the
remains of plant life.

3. Aeolian deposits.

(i.) Bone breccia. — A mixture of sediments usually
wind borne with large proportions of animal
bones. Such deposits are rare, and usually
found in caves or round drying desert lakes.

(ii.) Peet. (iii.) Coal. — Some peet and coal is
undoubtedly formed on the surface of the
land, although this must be very damp land.

(iv.) Nitrates. — Deposits of nitrate salts from de-
decaying seaweed or animal and bird excreta.

(To be Continued.)

16

THE TASMANIAN NATURALIST.

The Sea Elephant.

(Macrorhinus Iconinus).

Years ago sea elephants occurred on King Island, in Bass
Straits. The ruthless destruction of the early days of last cen¬
tury exterminated the species in Tasmanian waters, and for
probably a century there has not been a Tasmanian record. The
bleak shores of Macquarie Island shelter a few remnants of
former large herds, and it was probably a straggler from this
Southern outpost which reached Tasmanian shores last
Christmas.

The specimen was first noted at Orford, on the East Coast,
but early in January became stranded in Wedge Bay, where he
was secured by certain of the inhabitants. Fortunately, owing
to the foresight of a local resident, the skeleton was secured for
the Tasmanian Museum, and a detailed description will
probably he published by the Royal Society of Tasmania.

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