362 E. 0. Tlovey — Trap Ridges of the 



ridges present bluffs or very steep faces to the west, while 

 their eastern sides are gradual in slope. These ridges are all 

 low, none of them rising to a height of more than 140 feet 

 above the sea, though in Branford the sandstone rises grad- 

 ually to the height of 226 feet.* 



The most striking feature of the topography, however, is 

 that of the outcrops of trap. These arrange themselves in 

 about six lines of ridges, as is well shown on Percival's elabo- 

 rate and excellent map of the State, f and also on the map 

 accompanying this article. The most important range com- 

 prises Pond Rock (Percival's E. I.), and Totoket Mountain 

 (E. II.), which seem to belong to different systems ; while the 

 five subordinate ranges are made up of many small exposures 

 of trap, and lie two to the east and three to the west of Pond 

 Rock. With the exception of the easternmost, these ranges 

 show a general convexity toward the west, while Pond Rock 

 and Totoket are almost semicircles. The eastern of the six 

 ranges is very short, and is remarkable for being convex toward 

 the east — the only well-marked example of the kind in the 

 Connecticut Triassic area. 



The map accompanying this article has been prepared with 

 considerable care. Most of it was taken from the charts of the 

 ISTew Haven Region by the U. S. Coast and Geodetic Survey ; 

 but the region east of the road crossing Pond Rock, northeast 

 of Lake Saltonstall, and the southern hook of Totoket Moun- 

 tain were mapped by myself, using a compass and measuring 

 the distances by pacing. The town maps of the district as 

 given in an atlas of New Haven County were found to be 

 almost entirely valueless, even for the roads. The outlines of 

 the exposures of trap were all laid down from my own obser- 

 vations. I have endeavored to represent with approximate 

 accuracy the position and shape of every exposure of trap in 

 the region mapped ; the task required the location of about 

 270 exposures.:}; See further, tue closing note on page 383. 



Pond Rock. — Pond Rock, with the eastern ridges, is consid- 

 ered by Prof. Davis to contain the key to the whole problem 

 of the origin of the trap ridges of the valley, hence a detailed 

 description of this and the other ranges will not be out of 

 place. The main range, Pond Rock, begins \\ miles S. 10° E. 

 of the railroad embankment across Lake Saltonstall, and ex- 

 tends northerly and easterly for six miles. For rather more 



* Map of the New Haven region by the U. S. Coast Survey. 



f Report on the Geology of Connecticut, 1842; J. G. Percival. 



% The degree of excellence attained by Percival in his map is something mar- 

 velous. Working alone and without any of the modern appliances, he produced 

 a map which to-day stands very fairly the test of field work in a region of excep- 

 tional intricacy. The scale of his map is small, being but one inch to five and 

 one-half miles. 



