■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. 



