238 CALIFORNIA ACADEMY OF SCIENCES. 



several are believed to have been added to the fauna by 

 recent importation (mostly accidental), as they are not found 

 fossil there. 



2. PACIFIC SLOPE VARIATIONS. 



Having thus found that little if any post-tertiary changes 

 have occurred in the species of the Atlantic slope, it seems 

 astonishing to discover that there have been quite striking 

 changes in those of the Pacific slope, even in recent times, 

 and presumably ever since the tertiary epochs. These 

 changes are shown by the differences in fossil specimens 

 from the living forms, but have not been marked enough to 

 cause, so far, their separation as distinct species, chiefly 

 because intermediate forms exist. At the same time it 

 must be remembered that the extremes of variation are bo 

 great on this coast that many were at first described as dis- 

 tinct species which have since been connected by interme- 

 diate links. Here we have the examples wanted by disbe- 

 lievers in the origin of species by natural selection, who 

 claim that no transformations can be proved by fossil spec- 

 imens. There is probably no class of fossils so well suited 

 to demonstrate this law, or, if untenable, to disprove it. 



The most marked instances are found on the islands of 

 Southern California, where several species have swarmed so 

 profusely, but indications of similar changes are seen on the 

 main land in favorable spots, and even in the far interior 

 mountain regions of Utah, etc., where Mr. H. Hemphill found 

 such strange series of forms. The fossils of those regions seem 

 also to agree with the law of development by gradual 

 changes. In these instances we have a parallel to similar 

 ones known to have occurred on the islands and some parts 

 of the mainland of Western Europe and Africa, of which 

 we perhaps see the continuation still' progressing, in recent 

 changes caused by cultivation or geological oscillations of 

 the land known to be in progress. The effect of these os- 

 cillations is, of course, exerted through changes produced 

 in the climate, chiefly in amounts of heat and moisture. 

 (See Dana's Manual of Geology, Ed. 1874, p. 586-7.) 



