110 GEOLOGY OF THE TinRD DISTRICT. 



The great interest of all these metamorphic products, is that they have not been caused by 

 a dry heat, or fire, no evidence of the kind existing ; nor is any needed to effect the change 

 there observed, though it can, and has, and does produce the same results. All that is re- 

 quired, is the presence of the elements of the products observed at S3rracu8e, and in a state 

 admitting of solution and of moisture, to which every degree of heat added, v?ould greatly 

 aid their mutual action upon each other ; and from solution, crystallization would take place, 

 and thus metamorphic products or rocks would be formed, no igneous action commonly so 

 called being requisite, but a thermal one only. 



13. WATER-LIME GROUP. 



Water-lime Group of Manlius. Hydraulic Limerock of Eaton. 



(Part of No. 6. Pennsylvania Survey.) 



This group takes its name from the earthy drab-colored limestone, from which all the water- 

 lime in the district south of the Erie canal, with one exception, is manufactured. It consists 

 generally of dark blue limestone, and usually of two layers of drab or water-limestone ; the 

 two always separated by an intervening mass of blue. The group is well defined, and is 

 readily recognized in this State and in Pennsylvania, by its mineral nature, its fossils in par- 

 ticular, and by its position. It extends through the district with a thickness of not less than 

 thirty feet, often attaining to a hundred or more. 



Some of the layers of blue limestone have been deposited in the state of fine sediment, or 

 rather a sediment mixed with a calcareous precipitate, showing a striped or ribbony appearance, 

 and separating into thin straight courses in accordance with the stripes. 



In general the layers are extremely regular and well defined, usually about three feet thick, 

 but often four and even thicker. The courses into which the layers are sometimes divided, 

 instead of an even, show a crenulated or notched surface, like the sutures of a skull ; the two 

 surfaces interlocking with each other, and the projecting parts showing a fibrous structure, 

 caused in part by the crystallization of epsom salts, this effect taking place where the impu- 

 rities are in greatest amount in the rock. The layers and courses in the rock were caused by 

 the impurities which they contained, collecting in the seams or divisions, whilst the rock 

 admitted of the permeation of moisture or water. 



One of the layers, usually from four to five feet in thickness, is traversed by oblique cracks 

 in at least three directions, breaking the mass into irregular parts or fragments : this layer is 

 very fine-grained. It sometimes contains irregular nodules of flint ; and when these are 



