i^OBERT-" E. COWAN COLLECTION

IRESKNTED TO THE

UNIVERSITY OF CALIFORNIA

C. P. HUNTINGTON

dUNE, io--.

Glass'No,

-i^

. • V

.^K>

I

From the Proceedings of the California Academy of Sciences, February 1st, 1875.

The Origin of Culiforniaii Land-Shells.

BY J. a. COOPEE, M. D.

In previous articles I have giveii some observations on the Distribution and
Variations of the Califoruian Banded Land-shells, which naturally lead to the
consideration of their probable origin or past history.

In the "Bulletin of the Museum of Comparative Zoology," (Cambridge,
Mass., June, 1873, p. 202), Mr. W. G. Binn.-y writes, "the west alone is left
to us from whence to trace the Pnlmonate Fauna of the Pacific region, and
there the secret of its origin lies buried imder the Pacific Ocean."

Mr. Binney probably alluded to the supjiosed existence of a continent
ju the South Pacific, embracing the mountain summits now forming the
archipelago of Oceania, which became submerged, as Prof. Dana suggests,
during the later tertiary period, while most of California was emerging from
the ocean. ;

But even if this were proved to have happened, the great distance of the
nearest islands (the Hawaiian) from iis, and the great depth of the ocean
between, as well as north of them, besides the total dissimilarity of thtir
living laud-shells from ours, forbids any supposition ot a former land connec-
tion by which such animals could travel directly from one country to the other.
A glance at a globe shows that the islands, besides being tropical and wholly
south of lat. 23*^, are as far from us as the Aleutian Islands, the Arctic Ocean,
or i'lorida, and I propose to show that whatever migration to California has
occurred, came from the dii'ection of the regions named last.

No confirmation is given to a derivation from the west, by the more probable
former existence of an "Atlantis" connecting the two continents across the
Atlantic, the few island remnants of which really contain several species of
land-shells common to one or both sides.

The great similarity of our banded groups to those of Europe has always
been an argument for sui^posing them to have had a common origin. The
same similarity is found in many others of our animals as well as plants, and
is plainly connected with the well-known similaritj' of climates in the two
countries. But as the known laws of nature do not jjermit us to consider
climate as the cause of specific resemblances, we mu>t look for some other
way of accounting for them in this case.

The fact that very similar species exist in Japan and the Amoor Valley,
Siberia, contradicts, indeed, the theory of climatic causes, since we know that
the climate of those regions is very similar to that of our Atlantic States
where no similar species exist. At the same time, their existence there sug-
gests the probable central point from which all originated.

Going back in geological history to the sup^josed beginning of all living
species, few; if any, of the terrestrial, can be traced farther back than the

Eocene Tertiary, and most of them mnoh less far. But some included in the
comprehensive genus "Helix," are found fossil in the Eocene of Nebraska,
etc., suflficientl}^ like living American forms to be considered the "Darwinian"
ancestors of j)erhaios the whole of them! Or we may go back only to the
Miocene epoch, when trees scarcely distinguishable from the Californian
Kedwood and Libocedrus flourished in Greenland and Sj^itzbergen, between
lat. 70- and 78 . What is more natural than to su^jpose that land-shells also,
like those now living among our redwoods and cedars, existed in the shade of
those trees? I have no doubt that snch will yet be found fossil in the lignite
beds of the Arctic Zone.

It is easy then to see, that having their central j)osition (if not their origin) in
points so near the present North Pole, the subsequent gradual cooling of those
regions, which is supposed to have driven the living species of Redwoods
southward to California and Japan, as well as other trees into Europe, would,
if a slow change of climate, also drive southward the laud-mollusca " at a
snail's pace" into the same regions, where we now find their descendants
occupying countries, which are about equidistant in longitude, around the
northern hemisjihere, in lats. 40^-50-.

We have strong confirmation of this theory, in the well-known distribution
of circumpolar species of lind-shells southward, on both continents, along
meriliaus of similar temperature, and along mountain I'auges (especially those
running southward, as in America), and which are supposed to have thus
migrated south during the " Glacial Epoch."

Besides these two groups, the "circumpolar" and the "representative'
species, we also have on the west skqoe a very few of the Eastern American
ty23es. I do not, however, consider these as evidence of a migration weslward,
but would explain their occurrence as proving a former existence of ancestors
common to both, in the middle regions of Oregon and Nebraska, where are
found so many tertiary remains of animals that once inhabited both regions,
before the Eocky Mountains became a barrier to migration, or caused different
climates on the two slopes.

Tlie few fossil land-shells yet fouud in California are not sufficiently abundant
or ancient to furnish data for their geological history. The fresh water forms,
however, which I hope at some future time to describe and illustrate, indicate
a very different and more tropical group in the Pliocem^ and Slioceue strata.

The occurrence of Pupa and Conulus in the carboniferous strata of Nova
Scotia, shows that land-shells existed long before the Eocene period.

The great northern glacial drift, and local glaciers farther south, have so
generally destroyed the softer tertiary deposits that it must be long before the
routes of migration can be traced from Greenland southward, but as tertiary
land iilauts are found there fossil, some similar deposits must have escaped
elsewhere in the intermediate regions. Species much like the living ones
of California may be exijected to occur in the riiocene of British Columbia.

There can be no doubt that the local migration has been westward along
this coast, from the facts before stated as to the occurrence of sjiecies in the
coast ranges and islands, which are unquestionably not older than Pliocene in
age, while their allies in the Sierra Nevada may have existed there since the
Eocene, but at a greater elevation than they are now found. As they move

I

■westward, we also finci the few older forms developing,' into many "specialized"
varieties.

Going south uf California we find further conSrmation of the theory of
southward migration in Mexico, where species closely resembling the Pomatia
of Europe occur on the higher mountains, which, unless special creations,
could only havo reached the two regions \>y a process like that I have described.
The genera Bulimus, Glandina and Clausilm may also have traversed a similar
route, though tlipir absence in the tertiary strata of the Eastern States seems
to be evidence to the contrary. They may, however, be found in tho tertiary
of the Great Basin, which is known to contain fossils of some other genera
now found only S3uth of the United States (Berendlia and Holonpiirt). Indica-
tions, how(>ver, are known, which point to a connection of tropical regions
by land in tertiary times, independent of a polar route. The supposed
"Atlantis" connecting South America with Africa would also have connected
it mstwardly with Asia and Oceania.

The humble and despised snails thus become among the most important
evidences of geological changes and conditions of the laud, climate, etc., in
the past history of the globe. Being terrestrial and easily fossilized when of
moderate thickness, thty furnish evidence not supplied by any other class of
fossils, while their persistency of tyi^es is shown by the close resemblance
of the carboniferous species to modern tropical forms. One species at least,
which still lives in the Eastern States, is found only fossil in England (in
Pliocene or later strata) like the trees found under similar conditions, and
careful examination of fossil forms on both continents will no doubt show
other curious coincidences.

It may be mentioned also that genera of abundant occurrence in the Eastern
States have a few reijresentatives in Europe and Asia, as they have on this
Coast.

Every fact like this tends to prove that their former migrations have not
been to the east or west, but from a common northern centre toward the south.

V-

'^i ^l^m-

v'W^

' ^.*.-

^fv*-

r^ .

#.#>v^

S/. • •••1A5''

vx

K:«

r - <

3