CALIFORNIA ACADEMY OF SCIENCES. 251 



with the lower limit of glacial action on the high Sierras. 

 It seems probable that nearly all these lofty summits were 

 once covered by stratified rocks, which still remain in spots 

 as metamorphosed slates, as high as 13,400 feet. But the 

 more soluble limestone which still covers lofty ranges in 

 Nevada, and still exists above 5,000 feet in northern Cali- 

 fornia, seems to have been entirely denuded from the high- 

 est ranges during their upheaval, and since then, by the 

 erosive action of ice and water. This erosion has formed a 

 belt of tertiary detritus up to an elevation of about 6,000 

 feet near Kern River, and northward to 1,700 feet in 

 Bear Valley near Emigrant Gap. Here it contains fossil 

 tertiary shells of extinct species, relics of a pliocene lake. 

 The Big Tree Groves are along the upper edge of this alluv- 

 ial detritus, which like other fresh water formations proba- 

 bly contains much lime, and even limestone beds, at a depth, 

 not yet ascertained. So far, only the Big Tree Groves of 

 Mariposa County, at about 5,500 feet, and those of Tuo- 

 lumne and Calaveras about 4,750 feet, have furnished spec- 

 imens of the land shells common in those counties, while at 

 Bear Valley another species occurs. This formation consists 

 in part of volcanic materials, especially toward the north, 

 and the more or less recent epoch in which these have been 

 thrown out in various localities, no doubt has much to do 

 with the occurrence of animal and vegetable life. That such 

 rocks and soils, are suited for the growth of land shells if 

 there is enough moisture is shown by the Oregon fauna and 

 that of some islands on the Coast. 



I have also this year found H. Mormonum very stunted at 

 Alta, in Placer County, 3,600 feet altitude. There is also 

 evidence that the lower limestone stratum is exposed at 

 about 5,000 feet, near Emigrant Gap. 



Although no species have been reported from the interval 



of one hundred miles between Yuba River and Bass ranch, 



yet as most of the same species are found both north and 



south of this lava-covered section, and as limestone exists 



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