122 GEOLOGY OF THE SECOND DISTRICT. 



doubtedly chemical, and consisted in the separation of the siHceous and calcareous parti- 

 cles from the general mass, and of their segregation into central points of attraction. If, 

 under these circumstances, an impulsive or mechanical movement was given to it, those 

 centres of attraction, composed of siliceous or calcareous matter, could not but be obliged 

 to move on each other ; and the softer coating which surrounded, or in which they were 

 enveloped, would necessarily be pressed and compacted about the harder, which would pro- 

 bably result in the formation of polished, but flattened masses. 



3. Of calcareous shales. — They efl'ervesce briskly -with acids ; they consist, therefore, of calcareous and argillaceous 

 matter intimately mingled, and probably in about equal proportions, though they are more shaly than calcareous to 

 the eye. They are fine-grained, and destitute of lustre, but sometimes contain glistening scales of mica. Seams of 

 quartz and calcareous spar traverse the beds in many directions. GeoJes, containing crystals of quartz and lime, 

 are common ; or what is more frequent, the spar is in crystals, either in acute rhomboids or dodecahedral prisms. 



The color of this mass is bluish grey, with a texture very uniform. It is massive, and 

 does not split into flag-stone, and the pieces of the rock are quite angular. It is a durable 

 stone, and only slightly affected by the weather. Most of the shales and sandstones at 

 Lon-ain become yellowish brown by exposure ; and in this particular, there is a sensible 

 difference. 



In this mass, I never have been able to discover fossils, except some obscure markings 

 similar to fucoids. The materials composing it appear to have accumulated rapidly, which 

 might have interfered with the due performance of the functions of life. The thickness of 

 lliis mass is about sixty feet. 



4. Of thin beds of limestone, always fine-grained and earthy, and variously checked with seams of calcareous 

 spar. 



These beds may be considered as way-boards, or layers which mark the direction of the 

 planes of deposition. They are mostly impure, but sometimes may be employed for lime. 

 They are, however, rarely more than one foot thick ; and hence, under ordinary circumstances, 

 the labor and expense of quarrying are too great to be profitable. 



5. Of beds of fintij slate, with sharp cutting edges and conchoidal fracture ; color green and bluish black : per- 

 fectly close-grained, or compact like flint or jasper. 



The beds of flinty slate are often checked with seams of white or grey quartz, and some- 

 times with calcareous spar, and the surfaces covered with implanted crystals of lime, quartz 

 and sulphuret of iron. 



6 Of calcareous breccia. — The mass is made up of angular fragments of limestone and a slaty sandstone, be- 

 tween which there intervene seams of calcareous spar. 



It is sometimes in beds from thirty to fifty feet thick ; and so compacted together, and com- 

 posed of so much calcareous matter, that it may be employed for marble, as at Swanton, 

 Vermont ; but as it occurs along the Hudson river, it is unfit for this purpose, in consequence 

 of containing so much slate and dull earthy matter, and an imperfect incorporation of the 

 materials. 



