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 



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