GEOLOGY OF SARATOGA SPRINGS AND VICIXITY 121 



or more in diameter. In the balls they show but little sign of 

 corrosive action, but in the glassy, intervening matter they are 

 often considerably corroded by the igneous rock, resulting in the 

 production of most curious shapes (figure ii). 



In the specimen figured, the lava attack was probably from the 

 front instead of from the right hand, thus lessening the amount 

 of apparent corrosion, though a large margin remains. These cor- 

 roded inclusions are in the pitchstone, while those in the balls 

 show but little corrosion and but a trifling selvage of surrounding 

 glass. 



The two matters of chief interest concerning the inclusions are, 

 the source of the limestone and the reason for the absence of other 

 inclusions, especially those of shale. 



The limestone of these inclusions is slightly reddened, presum- 

 ably a result of heat from the lava, and is finely crystalline in 

 texture, likely due to recrystallization on heating, though this is 

 not certain. The inclusions are all of the one type of limestone. 

 They must have been brought up from below ground by the rising 

 lava, which must have passed through such a limestone formation 

 during its ascent. 



The only rock formation of the region which could have fur- 

 nished such material is the Bald Mountain limestone of the eastern 

 basin. In the western basin deposits we have the Hoyt and Amster- 

 dam limestones, but they are separated by the great thickness of 

 the Little Falls dolomite. Had the inclusions come from this series 

 there would unquestionably have been an abundance of dolomite 

 fragments in the lava, while actually there are none. But the 

 Bald Mountain limestone has shales above and below. It also has 

 many dolomite beds in its lower portion, so that it is surprising 

 that there are none in the lava, if the inclusions really came from 

 this formation. The question of the source of the inclusions 

 becomes of much importance in the discussion of another problem, 

 and we must later return to it. 



The knob is surrounded by black shales, chiefly Normanskill, 

 and it would seem that the lava must have risen through a large 

 thickness of such shale. There are also frequent beds of hard, 

 sandy grit in the shale. Under the circumstances the utter lack 

 of recognizable shale inclusions is most astonishing. There are 

 some large masses of shale involved with the lava but it is ques- 

 tionable if they can be regarded as inclusions. There are a few 

 grains of quartz observable in the thin sections, and one patch 



