62 



B. K. EMERSON — DIABASE PITCHSTONE AND MUD ENCLOSURES. 



'% 





TRAP 



SHALE 

 foUOES/CLOSt/RE 



Figure i.- 



-Section of Fault at House south of Dibbles 

 Crossing. 



Showing shales resting on the mud-filled surface of the 



trap. 



of the pores were left empty or only partly filled by the mud, and these 

 are filled with white infiltrated calcite, making a striking contrast. In 

 many cases it can be seen that the mud has risen from the stratified mass 

 of the argillaceous rock to form and fill the cavities. That the bubble- 

 like masses of mud have thus risen from this larger mass, and that they 

 are regularly disseminated in the trap and are not simply the filling of 



superficial steam holes, can 

 be clearly seen and the trap 

 can be chipped off and layer 

 Xsamostone after layer of the gray drops 

 seen to be isolated in the trap 

 (see plate 3, figure 1). 



In one case there can be 

 seen at the height of one's 

 eye, at the south end of the 

 west wall, a series of blocks 

 filled with drops, and the 

 mud mass from which they stream can be seen below, while now the mass 

 containing these mud amygdules is itself shattered and its fragments 

 cemented by more of the same mud (see plate 3, figure 2). In other places 

 a thin gray laminated sandy shale is confusedly mingled in the trap, its 

 layers being greatly warped and twisted. Under the microscope the 

 mixture can be seen to be still more intimate, and while there was often 

 a complete emulsion of the two non-mixing fluids, there is only a slight 

 chemical action discernible. Only a microscopic layer of recrystallized 

 carbonates appears.* 



In other cases the whole wall has a coarse conglomeratic look, rounded 

 portions of the trap as large as a fist being wrapped around by thick 

 flakes of the thin, fissile, sandy shale as if balls of putty had been sepa- 

 rated by being folded in thick wads of wet wrapping paper. 



Above this intimate mixture a few angular fragments of scoria are en- 

 closed for a foot or two in the thin bedded sandstones. This layer can 

 be followed north ten miles wherever the upper surface of the trap is 

 exposed. 



THE UNDERROLLED MATERIAL. 



The most striking circumstance in the whole matter, however, is the 

 fact that at the base of this great sheet, which is from 300 to 500 feet 



* If any one visits this most interesting locality, which is situated four miles from Holyoke, on 

 the road to Westfield, the ridge running from the Dibble house south to the next house will be 

 found cut by the railroad, showing the trap and the sandstone above. In the swale west of this 

 small ridge is a fault, which can be seen in the brook directly behind the second house (see 

 figure i). West of this fault the series is repeated, and the broad surface of the trap for a mile 

 north is filled with the foreign material. 



