MUSEUM OF COMPARATIVE ZOOLOGY. 123 
with the adjacent beds has already been mentioned. The base is seen 
in the Shore Line Railroad cut, locality 14’. The back of the sheet 
has been carefully searched from one end 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 subsequent 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 under 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 byiron. 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 Lamentation 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 from the frovt 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 the lower portion in contact with 
the sandstone. Pumpelly speaks of this fining of the texture on ap- 
1 Geol. Conn., 1842, p. 388. 
