60 GEOLOGY OF THE THIRD DISTRICT. 



The whole of the veins are but tlie east and west joints of the rock, where the conditions for 

 the secretion of their contents existed. They are of great importance as to the true theory of 

 veins, but of none whatever in an economical point of view ; the rock being expensive to work, 

 and requiring to be very rich in order to compete with the " lead diggings" of the west ; which, 

 though so far distant, are yet near to cheaply navigable waters ; and the ore, being profusely 

 distributed, and often in decomposed or altered rocks or cavities, calls for the use of the spade 

 oftener than the blast ; hence tlie term lead diggings, so frequently applied to those deposits. 

 This slate in the third district forms the surface, through which all the rocks of the uplift 

 have been protruded. It was therefore uncovered to a great extent before that action took 

 place, as is evident from its geographical distribution as it appears upon the geological map. 



6. HUDSON RIVER GROUP. 



Frankfort Slate and Rubblestone, Green Slate and ditto of the Reports, with the Shales of 

 Pulaski. Greywacke, or Metalliferous Greywacke of Eaton. 



(No. 3. Pennsylvania Survey.) 



This group consists of the Frankfort slate and sandstone, and the sandstone shale of 

 Pulaski, or shales and sandstone of that place ; the former name generally being more appro- 

 priate, as it contains more sand than shale, or what was mud or fine earthy sediment. The 

 group rests upon the Utica slate throughout the district, and is next in order as to age. It is 

 followed by the grey sandstone of Oswego, the rock which immediately succeeds to it in the 

 district where that rock exists. 



The name is adopted as being generally used in the survey, and as being more compre- 

 hensive than the one heretofore used. It is, however, objectionable, from the difficulty of 

 defining its limits along the region of the Hudson river ; from the disturbed and altered state 

 of the greater part of its rocks ; from the absence of those which immediately precede and 

 follow it, and which show its position in the class ; and from the difficulty of separating or 

 distinguishing the slaty or schistose members of the group, from those of greater age with 

 which, on their eastern border, the two are more or less really or apparently blended. These 

 objections are of no small import. The difficulty of the subject has led other geologists into 

 error, besides those of our country. There is now every feason to believe, that the facts in 

 relation to this group, leaving out the Pulaski portion, are the same in England as in the 

 eastern part of New- York ; that the group in England overlaps the lower rocks, extending 

 toward the primary, which there is to the west and not to the east, their relative position being 

 reversed ; and exhibits the same derangement, the same alteration of character, and the same 

 apparent mixture with more ancient schistose rocks, as in New-York. It is very certain also 



