I20 



NATURAL SCIENCE. 



basin took place, or at any rate was saved from the influx of the sea 

 by higher land. We find, therefore, no evidence that the sea ever 

 penetrated into the region after it became a basin, and there is no 

 evidence of the former existence within it of a marine fauna. 



Though the sea never penetrated into the Great Basin, there 

 was formerly a much heavier rainfall ; so that instead of the existing 

 deserts and salt-lakes, there were large sheets of fresh water, com- 

 parable in size with the Great Lakes on the other side of the 

 continent, and, like them, overflowing towards the sea. 



It is a most interesting region to the geologist, for the Great 

 Basin well illustrates the formation of lakes through irregular earth- 



FiG. 1.— The Great Basin and its extinct Lakes. After Gilbert and Russell. 



movements. The abandoned beach and shore-lines of the extinct 

 lakes, as Mr. Gilbert has clearly shown, are tilted and deformed in 

 a most remarkable fashion. 



The aquatic fauna of the Great Basin, as we should expect in 

 an isolated region such as this, where lakes expand and contract, 

 and their waters change constantly in chemical composition, is an 

 extremely poor one, and seems always to have been poor. From the 

 point of view of the naturalist, these nearly extinct lakes are, therefore, 

 of little importance, for their continuous isolation and the unfavour- 

 able conditions have prevented the appearance of a lacustrine fauna 

 and flora of any extent. 



