464 



GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS, 



the compact trap from Mount Holyoke (colunans 2 aud 3), and a mean of 

 the same (cohimn 4):' 



Analyses of trap from Mount Solyoke. 



THE UPPER OR POSTERIOR SHEET= AND ITS FEEDING DIKES. 



This bed (see PI. IX, p. 446) runs from a point on the Connecticut 

 River about a mile below the Mount Tom station, parallel with and about 

 a half mile east of the Holyoke range, to and beyond the south line of the 

 State, while its great iiTegular feeding dike is about 2 miles south of Smiths 

 Ferry and just east of Mount Tom, where on the map the outcrop swells 

 out suddenly. It is locally known as Little Mountain, and forms the culmi- 

 nating point of Forest Park, to which the Elective Road runs from Spring- 

 field and Holyoke. 



The trap sheet shows the low easterly dip of the sandstone, in which it 

 lies at a horizon about 600 feet above the Holyoke bed, though north of 

 Mount Tom the two beds seem to be much nearer because of the Mount 

 Tom fault, which at the cut south of the Mount Tom Electric Raih'oad 

 station brings them apparently within 30 feet of each other. The bed is 

 thick, but does not seem to extend east of the Connecticut, where the tuff 

 rests directly on the sandstone. Yet an inspection of the map may leave 



' Am. Jour. Soi., 3d series, Vol. IX, 1875, p. 186. 



^ Called thus by Percival in The Geology of Connecticut, because the trap ridges face west and 

 subordinate ridges often appear before and behind the m.iiu one. 



