6 Davis — Quarries in the Lava Beds at Meriden. 



posterior sheet does not here give decisive evidence of its 

 origin. 



The Quarry block will be described in detail below. 



In Cat-hole block, the anterior sheet is opened in a small 

 quarry near its base, where a ropy flow-structure is exposed. 

 The vesicular upper surface of this sheet is well seen, but no 

 actual contacts are found. The main and the posterior sheets 

 in this block have afforded no evidence as to their manner of 

 origin. 



In Notch mountain block, a water-worn fragment of vesicular 

 trap has been found in the sandstone about a foot above the 

 very scoriaceous upper surface of the anterior sheet. The 

 main and posterior sheets afford no evidence. 



In West Peak and Short mountain blocks, no exposures of 

 upper contacts have been found. 



Other blocks north and south of the Meriden district afford 

 repeated instances of " mixture " at the upper contact : for 

 example in the gorge of Farmington river at Tariffville.* It 

 should be understood, however, that while the lines of upper 

 contact — sandstone on lava sheet — must measure many miles 

 in total length, it is only here and there that they are exposed 

 to sight, and then for but a few feet. To the geologist not 

 familiar with these small but significant exposures, the suffi- 

 ciency of the evidence of extrusion in the several blocks may 

 be doubted, such is the prepossession in favor of " dikes " and 

 " intrusions " when dealing with igneous rocks. The sufficiency 

 of the evidence in one block to prove the extrusion of sheets 

 in neighboring blocks, where no contacts are found, may be 

 seriously questioned, so naturally is suspicion aroused when 

 stratigraphic continuity is broken : but after repeated observa- 

 tion on the ground I believe that, taken altogether, the evi- 

 dence of extrusion of the anterior, main, and posterior sheets 

 is overwhelming and incontrovertible. 



When the lava beds are once clearly recognized as extrusive, 

 they may be used with any other members of the rock series 

 in stratigraphic studies. The systematic repetition of the 

 anterior, main, and posterior ridges in orderly succession over 

 and over again, naturally suggests faulting : a line passing by 

 the northern end of one set of the three ridges will, if con- 

 tinued to the southwest, pass by the southern end of the set in 

 the next block : the lines of this kind also mark the termina- 

 tion on one side or the other of various minor ridges of sand- 

 stone on conglomerate : the same lines lead to the occasional 



*See an article by Professor W. North Rice, this Journal, xxxii, 1886, 430- 

 433. Also, The Intrusive and Extrusive Triassic Trap Sheets of the Connecticut* 

 Valley, by Davis and Whittle, in Bull. Museum Comp. Zool, xvi, 1889, 99-136. 



