66 BULLETIN OF THE 



The second argument is based on the arbitrariness of succession or 

 lack of relation between the different members of the series. Here the 

 interpolation of contemporaneous lava flows at certain points in the 

 series is significant ; for as far as is known they bear no necessary rela- 

 tion in the time of extrusion to the deposit of conglomerate, sandstone, 

 shale, or limestone. Professor Emerson has, it is true, regarded some 

 of the limestones that occur associated with the trap sheets in Massa- 

 chusetts as the product of thermal springs that were excited by the 

 eruption of the trap. I cannot say anything as to the cause of the lime- 

 stone deposit in Connecticut, but whether connected causally with the 

 eruption or not, the association of limestone and trap is by no means 

 invariable ; the limestone occurs only, as far as known, on the back of 

 the first trap sheet, and this in itself is enough to make one lean toward 

 the explanation by faults. If all the beds were sedimentary, and their 

 succession were of the normal kind described by Professor Xewberry in 

 his essay on " Circles of Deposition," the repetitions might perhaps be 

 explained without faulting; but it has been seen that such is by no means 

 the case. Before proceeding to the third argument, it may be noted that 

 the explanation thus far given does not depend altogether on the contem- 

 poraneous extrusive origin of the trap ; it is important to note this, for 

 while extrusion has been well proved for the first or Lamentation section by 

 observations on the previous day's excursion, it is not yet directly proved 

 for the High Rock section, although as will appear in the sequel there 

 can be little doubt that all the sheets of the district are extrusive. But 

 if intrusive, it is difficult to conceive that intrusive sheets should have 

 taken their places among the bedded rocks as systematically as these 

 Meriden sheets have, unless they had been driven in between the beds 

 before they were tilted, and then faulted afterwards. Therefore, whether 

 the trap is intrusive or extrusive, the evidence thus far collected favors 

 the hypothesis of faults, and of the eruption of the trap before faulting. 



The third argument by which decision is to be made between repeti- 

 tion by faults and by recurrent processes, depends on the number of times 

 the repetition occurs. If the two sections now described are the only 

 ones in the valley thus repeated, they might possibly be regarded as the 

 results of recurrent processes ; but if similar sections occur frequently 

 or habitually, with no more change in the corresponding members than 

 should be expected in different parts of beds of lava, sandstone, con- 

 glomerate, and shale, then there can be no question that the repetition 

 is due to faulting. It may be noted also that if faults are found in 

 some number and in systematic relation and accord, they may be ac- 



