WESTERN DISTRICT. 



291) 



of Mr. Geddes of Fairmount, which is excavated in the green plaster shales, contains from 

 •2 - 2 to 25 grains of saline matter to the gallon, which consists of the chlorides of lime and 

 magnesia, together witb the sulphate of lime, silica and alumina. Alumina and silica seem 

 to be present in most spring, well, and even river waters. The silica is, no doubt, often 

 in the form of infusorial shields and cases, as this class of animals are often abundant in 

 fresh waters. 



The water of the Genesee river contains 10-40 grains of saline matter in a gallon, con- 

 sisting of the sulphate of lime, silica, alumina, and lime in combination with an organic 

 acid. The quantity of saline matter is so small that the water washes, and may be 

 regarded as tolerably soft. It must be remembered that the river rises in a sandstone 

 district, which furnishes but a small amount of saline matter. The lakes, those especially 

 which ate excavated in the shales of the plaster and salt rocks, are more remarkable for 

 tin- amount of saline matter which they contain. As an example of this kind of water, 

 I may refer to the Green lakes of Manlius. These represent a large number of lakes 

 whose basins have been formed in this remarkable formation, either by subsidence or 

 by a peculiar kind of excavation. The basins bear a resemblance to a large crater ; the 

 sides being steep, and sometimes precipitous. The annexed sections illustrate the shape 

 and appearance they present : they were furnished by my friend Dr. Linklaen, of Ca- 

 zenovia, in the neighborhood of which place lakes in this formation are not uncom- 

 mon. 



In fig. 34, b represents a steep sloping bank, from one hundred and thirty to one hundred 

 and fifty feet high. The rock forming the bank is a shale of the Onondaga-salt group. 

 In the same series is the gypsum, which is quarried at a. The vermicular rock appears at c. 

 The depth is 156 feet at d. Whole diameter, 80 rods ; mean depth, 150 feet. The entire 

 depression, therefore, is 300 feet. 



Fig. 34. 



In fig. 35, the banks are perpendicular. In this case, the rim or brim of the lake is 

 formed by the Onondaga limestone. 



38* 



