East Haven- Br anford Region. 367 



range next west of the main range contains many amygdules 

 and pipestems of calcite at its southern end and the rock is a 

 dull black ; toward the north some of the ridges consist of hard 

 and somewhat lustrous trap, and others of that which is much 

 decomposed and soft ; some are amygdaloidal while others are 

 not. These ranges are composed of many isolated members, 

 and some variation might be expected. 



The main ridge is composed for the most part of a continu- 

 ous sheet of trap, but the external appearance and texture of 

 the rock vary somewhat in different parts of it. By far the 

 largest part of the sheet is composed of hard, dense, tough trap 

 which is almost as lustrous as that from East Rock, but its 

 color is a lighter green and planes of alteration penetrate its 

 mass. At the railroad cut the rock is somewhat amygdaloidal, 

 and much of it is decomposed, some even into coarse dark- 

 brown earth The solid rock at this place is green or black, is 

 almost lusterless, and rarely if ever shows its crystalline struc- 

 ture macroscopically. 



Along the lake, as has been remarked already, much amyg- 

 daloid occurs ; it alternates with the dense and the decom- 

 posed rock. The amygdules are mostly of calcite, which easily 

 weathers out leaving the rock very vesicular. Fragments of 

 this vesicular trap cover large areas of the southern slope near 

 the eastern extremity of the ridge. 



In Prof. E. S. Dana's collection of. thin sections there are 

 two from Pond Rock, one from the railroad cut and one from 

 the head of the lake ; in mine there are three : one from the 

 lower contact with the sandstone in the railroad cut, one from 

 near the middle of the sheet on the northern side, a mile and a 

 half from the lake, the third from the southern slope within 

 half a mile from the eastern extremity of the ridge, showing 

 the contact with the overlying sandstone. Prof. Dana's sec- 

 tions and the first and third of mine (Nos. 21# and 18 of the 

 collection), show very much the same thing, viz : an altered 

 diabase with the augite constituent almost entirely gone, and 

 with the plagioclase somewhat affected. The section (No. 23), 

 from the northern slope is very different from these. Consid- 

 erable chlorite appears, but much of the augite is apparently 

 but little altered, giving the usual brownish color in ordinary 

 light and bright colors between crossed Nicols. The structure 

 is rather coarsely crystalline and the individuals of the plagio- 

 clase twins are much larger than have been observed in other 

 sections. In this section the feldspar constituent seems to be 

 the one that has suffered most from hydration. 



]STo thin sections have been made of the trap of the first 

 range east of Pond Rock, but I have two (Nos. 15 and 25 in my 

 collection), from the second range ; the former is from the con- 



