382 E. 0. Hovey — Trap Midges of the 



it occurs, but also on account of the great size of the bowlders 

 composing it. In the southern part of the Connecticut valley 

 this heavy conglomerate occurs only in connection with the 

 ranges of trap southeast of Toket Mt. and those east of Pond 

 Rock, all of which are very near the eastern crystalline rocks. 

 The most probable sources of the trap in the conglomerate are 

 the heavy sheets near by, though the bowlders do not much 

 resemble the trap of the great ridges. But the conglomerate 

 does not affect the question of the intrusive or extrusive origin 

 of Pond Rock and Toket, for in each case much comparatively 

 fine sandstone containing no trap except such as forms a contact 

 breccia lies between it and the main ridge. The formation is 

 older than the ranges east of Pond and Toket; for the trap of 

 the range east of the latter lies on top of it, and that of the 

 ranges east of the former intersects it. 



The age of the trap.- — Professor Davis concludes that all the 

 trap was ejected before the tilting of the sandstone took place. 

 This does not appear to be true in the region I have examined. 

 The sandstone of the western part of the region was much 

 faulted and broken in the process of upheaval ; but the true 

 dikes do not appear to have been faulted, and therefore must 

 have been formed since the tilting of the strata. The fissures 

 through which the trap came up may have been made in con- 

 nection with the tilting. Pond Rock is an intrusive sheet, but 

 the evidence regarding its age seems to be incomplete. It is 

 certainly more recent than the youngest strata now exposed in 

 this part of the valley (except the trap conglomerate), for it is 

 intruded between them. The crescentic form, if we accept 

 Rogers's theory of its origin, might be taken as an indication 

 of intrusion after the tilting. If Pond Rock be of more recent 

 date than the upheaval of the sandstone, then the first eastern 

 range is still more recent, for its northern members separate 

 the strata of the conglomerate which was probably derived in 

 part from Pond Ruck. If we make Pond Rock intrusive after 

 the tilting, we must suppose the heavy trap conglomerate to 

 have been made later than the Triassic era ; which may be a 

 rather violent hypothesis, as unconformability between the 

 conglomerate and the sandstone has not been proven. The 

 second eastern range consists of dikes, as is shown by the dip 

 of the adjacent sandstone and the position of the trap with 

 reference to it ; and, on the. same evidence as is presented by 

 the western dikes, these are more recent than the tilting of the 

 sandstone. 



Conclusions. — My observations, then, lead me to agree with 

 Professor Davis in so far as to make some of the trap older than 

 the very last of the sandstone formation. Probably Pond 

 Rock is this older trap ; and the southern part of the range 



