East Haven-Branforol Region. 381 



H. D. Rogers proposed a theory to account for the crescen- 

 tic form of the ridges in New Jersey, which will hold very 

 well for those in Connecticut, especially if the theory just pro- 

 posed to account for the dip of the underlying sandstone be 

 correct. He 'said: " The sandstone being disrupted in a plane 

 parallel to the dip, the beds on the upper side of the sloping 

 dyke will be lifted off from those upon which they reposed, 

 and in this tilting of the beds, there will arise towards the 

 extremities of the fissure seams or transverse cracks extending 

 in the direction of the dip."* This theory readily accounts for 

 the conformability of the overlying sandstone in the "hooks," 

 for the trap flowing into these transverse cracks would modify 

 the dip of the upper sandstone so as to make its direction more 

 or less nearly the same as the slope of the upper surface of the 

 intrusive rock. That the fissures were sometimes originally 

 curved is shown by curved dikes and lines of dikes in the 

 region west of Pond Rock, while the curved outline of many 

 of the ranges in the whole valley is produced by what Percival 

 calls the ''advancing or letreating order" of position of nearly 

 straight fissures. It has been shown experimentally that when 

 one set of fissures is produced in strata, another subordinate set 

 transverse to them may be produced at the same time ; this 

 fact would explain the network of dikes east of Foxon in the 

 northern part of East Haven. 



Hemingway mountain is another of the trap ridges in the 

 region which Professor Davis has claimed to be overflow sheets. 

 Its intrusive character is shown at its northern end where the 

 extremity of the trap sheet stands between walls of sandstone, 

 both of which have been much indurated and otherwise 

 affected by the heat of the trap ; and is also indicated by the 

 trap of the ridge next west, which is exposed almost horizon- 

 tally between strata of sandstone, the upper of which it has 

 penetrated and scorified as well as hardened. North and north- 

 west of Hemingway mountain, within a mile, there are several 

 high ridges which seem to be dikes; they begin and end 

 abruptly and both sides are precipitous, while the outliers of 

 some of them are seen squeezed in between layers of sandstone. 

 The sandstone has been indurated to such an extent and degree 

 that it stands in ridges as high as those of the trap with sides 

 almost as steep. 



The heavy trap conglomerate south of the north end of Pond 

 Rock is a puzzling factor in the problem, not only on account 

 of the trap in it and its relation to the trap ridges near which 



* Tl lis Journal, xlv. 33 \. 1843. "Report of meeting of the Association of Ameri- 

 can Geologists and Naturalists. At this meeting a committee, consisting of Professor 

 Silliman, J. D. Whelpley and FL D. Rogers, was appointed to determine, if possi- 

 ble, the correctness of this theory. I have not found any report of the results of 

 their investigations. 



