TnE DEEKFIELD SHEET. 419 



the Connecticut, through Greenfield and Deei-field, and, turning eastward, 

 crosses the river and ends in Mount Toby. It is at first inchided in tlio 

 Longmeadow sandstones, and continues soutli in them until, at its south 

 end, it runs oft' into the conglomerate of" ]\Iount Toby. 



It has thus the characteristic elongated U shape which apjjears on a 

 scale so much larger in the Holyoke range. It is worth}- of note that the 

 high western border of the valle}^ which I shall elsewhere try to i)rove to 

 have been caused by faulting, c-orresponds in direction with both these 

 sheets, being set back in Greenfield and Northampton so as in each case to 

 present a reentrant angle to the northwest corner of the trap ranges, with 

 sides parallel to the con-esponding portions of the ranges. 



The bed is about 21 miles long, and where the Deei-field River breaks 

 through it it is about 100 feet thick; at Fall River, 1G5 feet. Where it is 

 cut by the artesian well of the Montague Paper Company (see p. 380) it 

 was penetrated 110 feet, which, with the dip of 40°, would give a thick- 

 ness of 84 feet. 



CONTACT ON THE SANDSTONE BELOW; THE UNDER-ROLLING OP THE CRUST AND 

 THE ALTERATION OF THE DIABASE BY HEATED WATERS TO A PITCHSTONE- 

 BRECCIA AND A DIOPSIDE-PLAGIOCLASE ROCK. 



Going southward from the bridg-e over Fall River, one finds in tlie 

 roadside, just before coming to the mouth of the stream, a contact of the 

 diabase upon the sandstone below — a granitic sandstone, coarse to medium 

 in grain, which is baked for an inch into a l^lack hornstone and changed 

 for a foot into a strong quartzite. The trap above is little aftected. 



Opposite Mrs. G. P. Heyward's, in Greenfield, and underneath the 

 lookout tower which stands on the crest of the trap ridge, a crushing machine 

 has been set up to supply the city with road material. For a long distance 

 the vertical wall has been cleared and a most interesting contact is exposed. 

 (See PI. VIII.) 



Climbing up from the sand fiats, over 60 feet of fucoidal sandstones 

 with strike N. 10° E. dip 40° E., one finds, at the base of the great trap 

 sheet and resting on the sandstone below, a layer 60 feet thick, made up of 

 rounded and angular blocks of traj), of all sizes up to 3 feet thick, the whole 

 mass penetrated by veins of fine red and black sandstone, often 6 inches 



