MUSEUM OF COMPARATIVE ZOOLOGY. 123 



with the adjacent beds has already been mentioned. The base is seen 

 in the Shore Line Raih-oad cut, locahty 14'. The back of the sheet 

 has been carefully searched from one ei^d to the other with no success 

 except in the little gully in its northern hook, locality 14 (Fig. 2), but 

 the general uneven and scoriaceous texture of its upper portion is con- 

 tinuously visible for two miles or more as it dips under Saltonstall Lake ; 

 this is seen to best advantage by rowing along the shore in a boat, 

 which may be obtained at the southern end of the lake. 



The base of the trap sheet for a distance of several feet is decidedly 

 amygdaloidal and close-grained ; and, owing to its broken character and 

 the subseqiient infiltration of secondary quartz and calcite, it locally 

 resembles a breccia. Under the microscope, the trap is seen to be very 

 amygdaloidal, and the vesicles are elongated by the flowing of the trap 

 conformably to the line of junction with the sandstone below. Speci- 

 mens of this breccia-like mass appear identical to the eye and imder the 

 microscope with those from the base of the anterior at the north end of 

 Totoket Mountain, locality 4. 



Round areas of a brownish material resembling water-worn fragments 

 of sandstone are apparently enclosed by the trap near its junction with 

 the sandstone, but the microscope shows these to be secondary deposits 

 in vesicles, and to consist of quartz and granular calcite, products of 

 alteration, stained brown by iron. Similar areas are found at the base 

 of a trap ridge on the northeastern limits of New Britain, locality 25, 

 where Percival erroneously refers to them as consisting of dark red jas- 

 per, the product of the indurating action of the trap ; ^ also at the base 

 of the tufaceous bed of the anterior to Lam. tation Mountain, local- 

 ity 8, and at the Hartford City quarries, locality 19. A section of sand- 

 stone three inches below the trap sheet of Saltonstall shows water-worn 

 fragments of trap, and denotes that at the time of the deposition of the 

 sandstone layers there were bodies of trap undergoing erosion in the 

 neighboring region : they may have been derived fi'om the front of this 

 very sheet before it had advanced .so far as the locality in question. 



The upper surface of the trap forming Saltonstall Mountain is ex- 

 tremely vesicular and irregular; the vesicles are sometimes well defined, 

 sometimes vague, indicating both gas expansion and replacement as 

 their cause. The texture shows a distinct decrease in coarseness as we 

 approach the upper contact, although the upper portion, as a general 

 rule, is more coarsely crystalline than tha lower portion in contact with 

 the sandstone. Pumpelly speaks of this fining of the texture on ap- 



1 Geol. Conn., 1842, p. 383. 



