XiUthek — Geology of the Salt District. 



217 



The cavities in some of the septaria in this horizon at Livonia and Le Roy 

 were found to contain a small quanity of petroleum, and iron pyrites is abun- 

 dant in both the shales and concretions. 



The overlying shale next above the limestone is very black but becomes 

 lighter colored by almost imperceptible gradations, and somewhat calcareous 

 owing to the presence of great numbers of LiorJiynelms. 



The upper limit of the Marcellus is not established by any marked change 

 in the character of the rock but is understood to be at the top of the beds that 

 contain Liorhynchus Hmitaris abundantly. 



Drilling through the Marcellus shale is easy and rapid, and there is only 

 the difference in color to indicate to the driller a change from the Hamilton 

 shales above. 



This formation is the horizon of the mouths of the wells in which rock 

 salt has been found in the village of Le Roy, the one at Teasel Hollow in 

 Caledonia, and possibly the one at Batavia, are in the Marcellus shale. 



East of the Genesee river the salt beds do not extend as far north as the 

 line of Marcellus outcrops. 



The light colored Hamilton shahs come to the surface frequently over 

 a belt of country averaging about five miles wide in the eastern part of 

 the district and eight miles in the western part, and embracing a portion of 

 most of the valleys of the Finger lake region, in which hundreds of deep 

 ravines have been excavated in the sides of the hills where the strata are 

 exposed to the greatest advantage. 



In Madison and Onondaga counties this group of strata is about 1000 

 feet thick, if 200 feet be allowed for the Marcellus shale. It diminishes gradu- 

 ally toward the west, and in the Oatka valley, in Wyoming county, it is not 

 more than 400 feet at the outcrop. The thickness increases at the rate of 

 eight to ten feet per mile toward the south in the western part of the district, 

 ami fifteen to twenty feet in the eastern part. 



Its greatest thickness in the salt district is 1142 feet as found in the 

 Ithaca test well, and its least 395 feet, in the Pioneer well at Wyoming. 

 At Livonia it is 517 feet thick. 



The lower beds differ little from the upper part of the Marcellus, except in 

 the character of the fossils, and in being somewhat lighter colored. They are 

 generally dark brownish or bluish grey when freshly excavated, weathering 

 to an ashen grey. The variation in color sometimes gives to the vertical walls 

 of the ravines a banded appearance. These lower shales are very soft and 

 disintegrate rapidly. The fossils are small and not usually very well pre- 

 served, except in the abundant calcareous concretions. 



