188 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



THE LIMESTONE BEDS. 



Before the introduction of railroads these beds of impure limestone 

 were of great im])ortauce, and they are fully treated by President Hitchcock 

 in all his works on the geology of the region. They are black, graphitic 

 and biotitic limestones, not often above 30 feet in thickness. The bed west 

 of Coleraine callage and that in Whately are the thickest. They have been 

 mapped for me with great care by Mr. William Orr, jr., of Springfield. 



They "increase in number tOAvard the north and toward the east, and 

 are most abundant in Ashfield, Conway, and Coleraine, and they continue 

 right up t(^ the LeN'den argillite, in which they are wanting. 



In the southern tier of towns occupied by these schists two very nar- 

 row beds appear in Montgomerj'; in the next tier to the north none were 

 found. In the next a few unimportant beds occur in Goshen. In the next 

 tier they are abundant in Conwaj', etc., as detailed above. 



These limestone bands are generally capped above and below by a thin 

 layer, 3 to 4 inches thick, of a black, compact, quartz-hornblende rock, often 

 studded with well-formed black garnets ( cc 0), which are connnonly called 

 melanite, but which are a common red, lime-iron garnet, colored black 

 by carbon. These bands have been formed at the expense of the lime- 

 stone, and often one finds beds Avhere the limestone has been altered 

 entirely; and where a bed thins out to 6 or 8 inches it becomes wholly 

 hornblendic. The mica in the limestone is arranged in rude sjDherical 

 concretions of the size of a walnut, and these two structures explain 

 (rt) the curious "anvils" — the columnar and mushroom forms on square 

 pedestals, which are so common in the limestone region — and (h) the 

 rough, warty surface of these peculiar forms and of the weathered lime- 

 stone everj-where. 



The process of the formation of these anvils is as follows (see PI. 

 XXXIII) : Jointing separates a square block of the limestone, with its caps 

 of amphibolite. The latter is more resistant, and weathering eats deeply into 

 the limestone, forming anvils, stools, or, where only one band of amphibolite 

 is preserved, columnar forms, warty from the projections of the mica con- 

 cretions. They are found most commonly in swamp}- places, where the 

 solution of the limestone has been favored. 



President Hitchcock made many analyses of the limestone, which are 



