68 



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



way through the whole thickness of the trap sheet in a throat three rods 

 wide and flowed out on the surface as a submarine mud volcano. As 

 shown below in figure 2, the walls of the throat are clearly exposed. 

 At the lowest point visible the trap is rudely columnar and compact. It 

 graduates upward into a scoriaceous trap, and this is covered by a layer 

 5 to 6 feet thick, made up of angular blocks of the same scoriaceous 

 trap, which are slightly moved on each other. This is plainly the un- 

 disturbed surface of a normal lava flow. 



The mass that rises in the throat and spreads over the lava sheet has 

 all the peculiarities of the breccia farther south. It contains the rounded 

 bomb-like trap blocks, isolated blocks of indurated white sandstone con- 

 taining blebs of pitchstone and rounded by abrasion ; blocks of scoriace- 

 ous red sandstone, also containing pitchstone and fragments of the jet- 

 black; fine-grained basal trap, often full of the long steam tubes which are 



SP-S-r.-.rr: rr 



m m& 



::/.r..--VK- 



tttttp^t* 



sandstoajs 

 \6lass brecc/a 





Dv?; " 



iliWi 





w 



'COMPACT TPAP 



Figure 2. — Generalized Section of Overflow of Glass Breccia through Trap north of Meriden. 



usually found at the bottom of the trap, together with various other trap 

 varieties. The whole is cemented by glass, and the secondary albite- 

 calcite-diopside mixture, as in the other cases. It rises over the lips of 

 the throat and flows southward. It graduates up into a tufFaceous sand- 

 stone, bedded by water, and full of ferruginous concretions. The breccia 

 can be followed north about 30 rods. I traced it south about 40 rods. 

 It is doubtless continuous with the two thin layers of tuff in the sand- 

 stone above the trap east of the ash bed described in the last section, 

 which were mentioned by Davis and Whittle.* 



" An interesting point is the occurrence of two thin layers of tufa in the sand- 

 stone just above the trap, each about an inch in thickness and about a foot apart. 

 These layers appear in a hand specimen of a rusty brown color, composed of water- 

 worn fragments of trap mixed with clastic quartz, and have a much weathered ap- 



* I,oc. cit., p. 120. 



