ROCHESTER AND ONTARIO BEACH QUADRANGLES 15 



limestone are often found made up largely of the fossil Pentamerus 

 and fragments of crinoids. 



The Wolcott limestone has the appearance of a crystalline lime- 

 stone, and on account of its power to resist heat it has been used as 

 a firestone for chimneys, hearths etc. 



Associated with it are a number of minerals, some of which 

 are found in cavities in the rock and sometimes in geodes. Of 

 these, gypsum, barite, chalcopyrite, malachite and several varieties 

 of quartz, including chalcedony and carnelian, are the more 

 numerous. 



Williamson shale. This division is well developed in Wayne and 

 Monroe counties. West from Monroe the formation is less developed 

 and on the Niagara river it is not found, the Irondequoit limestone 

 resting directly upon the Wolcott limestone. As the Furnaceville 

 ore is also absent we have but three of the five divisions of the 

 Clinton represented at Niagara. 



The Williamson shale is 24 feet thick at Rochester and like the 

 other divisions of the Clinton, it is best shown in the gorge of the 

 Genesee. The shale is shown in both banks of this river, above 

 the middle falls and extending north from the lower falls in the sides 

 of the gorge. 



As it occupies a position between two limestones it appears in a 

 marked contrast where the total thickness is shown. 



When the position of this shale is not indicated by the presence of 

 the limestones either above or below, it is likely to be confused with 

 the Sodus shale, specially when the outcrops have been badly weath- 

 ered. The Williamson shale may, however, in most cases, be distin- 

 guished from the Sodus shale as below indicated. The Williamson 

 shale is not of so uniform green color and interbedded in it is a 

 number of purple bands. The mass as a whole is very fossiliferous 

 and in it are found two or three thin bands of pearly limestone. 

 These limestone bands are made up of closely crowded shells of 

 A n o p 1 o t h e c a h e m i s p h e r i c a, to which they owe their pearly 

 luster. These limestones often project from the shale and form 

 small ledges. Interbedded in this formation there are also found 

 some very dark thin shales containing graptolites in great profusion. 

 It is of interest to note here that in New York this bed of graptolites 

 marks the highest horizon at which they are known to exist in 



