THE LIMESTONES. 265 



Herkimer and Hamilton counties. Similar patches occur in the region 

 under consideration, in addition to the extensive belts. 



The limestone in all of these belts is highly crystalline, rather coarse, 

 and usually light gray or white, though darker gray ])ortions occur. 

 Of the disseminated minerals phlogopite, graphite, pyroxene and 

 tremolite are most common. They may be evenly distributed or segre- 

 gated in lumjis, tlie tendency toward the latter mode of occurrence being 

 less marked than in the eastern section. 



In general the limestone is very massive, so that it is difficult to ascer- 

 tain the strike and dip with any degree of accuracy. When observable, 

 the former is generally northeast, the latter northwest, though exceptions 

 to the rule are common. 



Intimately associated with the limestones are several varieties of 

 gneiss, which may ]>e roughly divided into garnetiferous and micaceous 

 on the one hand and pyroxenic and hornblendic on the other. Of the 

 former group some are distinctly interbedded with the limestones, while 

 others are of doubtful relation. Among the pyroxenic and hornblendic 

 rocks many have the appearance of interbedded members, but others, 

 both in composition and in structure, closely resemble somewhat modi- 

 fied intrusions. 



Wherever these hornblende and pyroxene rocks appear they show a 

 great amount of crumpling and crushing. This ranges from slight pli- 

 cation to most elaborate contortion, followed by crushing of the rock 

 until, in extreme cases, it is reduced to a mass of angular fragments 

 held together by a paste of limestone. In this way remarkable breccias 

 are produced, whose origin might be obscure but for the fact that every 

 step in the process of their formation is shown. In all such cases the 

 limestone displays little or no sign of structural change, having the 

 appearance of a plastic mass in which the contained layers could be 

 twisted to any extent. It must be noted, however, that a large amount 

 of crushing and distortion in the limestone might be completely ob- 

 scured by subsequent recrystallization. These facts make it ai)parent 

 tliat when the limestone is free from gneissic layers it may present a 

 massive and undisturbed appearance, and yet have been subjected to 

 intense mechanical strains. 



This is a matter of imi)ortance in considering tlie question of themet- 

 amorj)liism of tlie series, for wliile the character of the limestone as a 

 whole might be thought to |)()int to an absence of any considerable me- 

 chanical disturbances, the plu'nomena of tlie crushed gneiss sliow that, 

 as a matter of fact, the series has l)een sul)je(;te(l to intense ))ressure. 

 The plastic nature of the limestone must also be taken into account in 

 all eftbrts to work out the structure of tlie series, as it is lia])lc to intro- 

 duce complications which may be the cause of much inaccuracy. 



