454 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



limestone, but here and there a large crystal has developed porphj^ritically, 

 enveloping the dusty ground in which it grew. In several cases live scale- 

 nohedra are joined at base to form a star. In one place is a rouud section, 

 4"" across, of coarsely granular and clear calcite without the dusty matter 

 of the rest of the limestone, and with its large grains untwinned, which 

 projects half into the limestone and half into the trap, as if the two had 

 been plastic together and a steam hole had been formed at the border. 

 Another oval body of the same size as the above is composed of the same 

 clay-dusted granular limestone as the large fragment, but has a border of 

 larger grains, and, while retaining its shape and individuality, is tlu-ust 

 a third of its length into the main mass, while two-thirds its length projects 

 into the trap. It seems here also as if the large mass must have been 

 plastic and impressed by the smaller one. The limestone fragment itself 

 has straight sides and shows a distinct contact effect, its mass being slightly 

 reddish, while a border 2"" broad is greenish and is separated from the 

 reddish interior by a band of black cubes, apparently altered pyrite. 



The endomorphic changes in the trap are much more marked than in 

 the former case. A zone 2^™™ wide is made up of a red-brown base in 

 which the few and distant feldspars appear like windows. A broad, clear, 

 brown halo suiTounds each feldspar and an oj^aque brown mass fills the 

 scanty interspaces. This gives the groundmass a curdled ajipearance. It 

 contains beautifully sharp calcite crystals, scalenohedi-a and rhombohedra. 

 With higher magnifying power the ground is resolved into a fine hyalopilitic 

 groundmass made up of beaded threads ^ to i^™™ across and ^""" long, 

 radiating in tufts from the feldspars and showing aggregate polarization 

 and black cross. It polarizes in blue colors. This felt of fine threads is 

 beaded with a black dust to make the more opaque portion of the ground. 

 This zone passes gradually into the normal diabase. 



A contact of the trap with the sandstone below is exposed in the road 

 leading up to the Nonotuck House, showing a distinct but not important 

 induration of the sandstone. It contains the same inclusions of limestone. 



The diabase at its contact with the sandstone below, at the northwest 

 shoulder of the peak next southwest of the Nonotuck House, is for a height 

 of 7 feet kneaded full of fragments of a fine-grained buff sandstone, and the 

 ti'ap itself is filled with dark-green amygdules. The sandstone effervesces 

 only at its contact witli the trap. The diabase is greatly decomposed, only 



