1883.] NATURAL SCIENCES OF PHILADELPHIA. 135 



form another series, characterized by several points of resemblance 

 in their fish faunjie. Whether they were connected, forming a 

 single body, at an earlier geological period, is not yet known. 

 Some of them are connected by rivers and creeks at the present 

 time, and the Klamath River discharges the contents of the lakes 

 of the same name into the Pacific Ocean. 



Still another late tertiary lake existed in Eastern Oregon and 

 Western and Southern Idaho. No body of water represents it at 

 the present time, and the remains of fishes found in its sediments 

 belong to species different from those of the Oregon basin, both 

 recent and extinct. It is to be supposed tltet this lake was 

 separate from all of the others, and of earlier age, although one 

 of the pliocene series. It may be called Lake Idaho, and its 

 sediment, the Idaho formation. A list of its species will be 

 given after the consideration of the characters of the faunai 

 of the Lahontan and Klamath Lakes. 



The cause of the desiccation of the Great Basin and other 

 interior regions of our continent, has not been satisfactorily 

 explained. It is usually ascribed to the intervention of the Sierra 

 Nevada and Rocky Mountain ranges, which precipitate the clouds 

 from the Pacific Ocean, and thus deprive the regions eastward of 

 rain. This would at first appear to be a sufficient explanation, 

 but the facts of geological history contradict it. The existence 

 of extensive lakes throughout the now dry region, in pliocene 

 and postpliocene time, has been already referred to. But the 

 Sierra Nevada was no less elevated then than now. Furthermore, 

 great lakes or seas occupied the centre of the continent during 

 miocene time, when the ranges were still higher. Yast forests of 

 vegetation, and a rich population of animal life, point to a humid 

 climate during the entire period that has elapsed since the great 

 elevation of the Rocky Mountains in the beginning of the eocene 

 epoch, to within comparatively recent times. Yet the mountains 

 have been steadily diminishing by erosion throughout that period. 

 ■^ Of course the comparatively low elevation of the Great Basin 

 would accelerate its desiccation, other conditions being equal. 

 Mr. J. D. Clayton,^ of Salt Lake Cit}^ discovered immense faults 

 along the western slope of the Wasatch Mountains, and proposed 

 the hj^pothesis that the entire area of the Great Basin had de- 



^ Published, I believe, iu a number of the Salt Lake Herald, which I 

 cannot at present lay my hands on. 



