Associated Limestone. 215 



marlite takes a large quantity of lime into its composition, it becomes 

 bituminous limestone ; and perhaps some of this variety may be found 

 in West Springfield. It is also said to occur in Southington and 

 Middletown, Ct: and the fetid limestone, also, (all of them connected 

 with the new red sandstone,) in Northford, Ct. 



At Turner's Falls, on the north shore, I found, a few years ago, a 

 stratum of coarse argillaceous limestone a foot thick, which was 

 neither bituminous nor fetid: but the subsequent removal of the 

 dam over Connecticut river, has covered the spot beneath the waters. 



On the banks of Westfield river, in West Springfield, we find lay- 

 ers of what appears to be an argillo-ferruginous limestone, interstrat- 

 ified with the slate, and only a few inches thick. Where the water 

 has laid bare this rock, it sometimes presents the whole surface divi- 

 ded into small prisms of only a few inches in diameter and length, 

 whose axes are perpendicular to the planes of the strata. They have 

 four or more sides, though irregular, and their sides do not touch. 

 They appear to have resulted from the same cause as the septaria 

 already described ; and I doubt not that both the septaria and these 

 layers of argillo-ferruginous limestone, might be employed, as the 

 former is in Europe, for the preparation of valuable Roman ce- 

 ment. 



From this sketch of the mineralogical characters of this group of 

 rocks, it will be easy to distinguish between the lower beds, which 

 have heretofore been considered as the old red sandstone, and the 

 upper ones, which have been called a coal formation. The lower 

 beds are distinctly stratified, but rarely slaty ; whereas the upper ones 

 are usually so ; although some varieties of conglomerate, scarcely 

 exhibit any marks even of stratification. In the lower beds is no 

 shale. Their color is almost uniformly some shade of red : but as 

 already shown, the upper beds are of various colors and shale is 

 abundant. 



The greater abundance of granite nodules in the conglomerate of 

 the lower beds of this formation, than in that of the higher has led 

 some geologists to regard them as belonging to distinct formations. 



But as a general principle, it will not answer to conclude that con- 

 glomerate to be the oldest rock, which contains rounded masses of 

 granite. For a deposite of granite might be so situated, that an abrad- 

 ing current would tear off large quantities of it, while much later 

 rocks might flank its sides in such a manner as to be almost entirely 



