MESOZOIC TIME — TRIASSIC AND JURASSIC. 



805 



1348. 



e/eet. 



Trap bluff at Greenfield, Mass., with 

 breccia of sandstone blocks (the 

 part Tt cemented by trap, and Ts 

 by sandstone) lying between it and 

 the sandstone S. B. K. Emerson, 

 '92. 



While the West Rock section, Fig. 1347, indicates, not only a great 

 amount of abrasion, but also a shoving forward of the abraded material 

 beyond or west of the place in view, that of the second trap belt east of the 

 Saltonstall Ridge has the abraded material 

 resting on the underlying sandstone in the 

 form of rounded and angular stones of the trap 

 and sandstone ; the accumulation was evidently 

 made, as Hovey states, by the friction between 

 the liquid and solid rock. 



B. K. Emerson reports that the trap sheet 

 of northern Greeniield, Mass., where the bluff 

 or trap faces westward (the dip being east- 

 ward), as shown in Fig. 1348, rests on a bed 

 of coarse sandstone breccia, 12 to 16 feet thick, 

 the upper part of which (^Tt) is cemented 

 by trap, which extends from above between 

 the blocks, and the lower part, 6 or 8 feet 

 thick {Ts), by red sand, which is continu- 

 ous with the underlying sandstone. More- 

 over, the bed of trap breccia rests on unbaked 

 sandstone. At a locality in the Mount Tom 

 Ridge, in the town of Holyoke, the base of the 

 trap, according to Emerson, is " kneaded full of 

 dove-colored limestone," looking "as if the limestone and trap had been 

 plastic at the same time " ; and at one place, where the trap is about 300 

 feet thick, its " upper surface is filled in the same way with the same lime- 

 stone to a depth of 8 or 10 feet." The limestone had been torn off from a 

 layer not visible in the section ; for, as he says, only sandstone is there in 

 view, or was found in a boring carried down 3500 feet. 



The large north-and-south belts of trap often have an attendant belt on 

 the east or west side, or on both, which is generally made of hydrous and 

 amygdaloidal trap, even when the trap of the large belt is of the normal 

 anhydrous kind. Percival draws special attention to this feature. The 

 Mount Tom Ridge is thus attended, as the map on page 801 shows, from 

 the Meriden region northward ; the line, which is low from denudation, is 

 on the western side through the southern part of the Mount Tom Ridge, 

 and on the eastern side for the more northern part. Saltonstall Ridge has 

 a similar parallel belt to the east, and another to the west of it, only a few 

 hundred yards distant, and each is perhaps of like relations to the "attendant" 

 dike of the Mount Tom Ridge. 



Tfte time of the eruptions and their relation to the upturning of the sand- 

 stone. — The evidence is complete that eruptions of trap preceded, as held 

 by Emerson and Davis, the deposition of part of the sandstone. The sand- 

 stone of East Haven, east of Saltonstall Ridge, contains stones of trap at 

 many places, as described by E. 0. Hovey, while none are known to occur 



