116 BULLETIN OF THE 
4.—Special Accounts of the more important Localities. 
The following more extended descriptions of certain selected localities 
are added, to give a better understanding of the fulness of evidence on 
the question in discussion than could be obtained from the foregoing 
summary. We thus present examples of what we interpret as an in- 
trusive sheet at Roaring Brook, on Gaylord’s Mountain; a bed of vol- 
canic ashes and bombs, presumably near the locus of eruption of one of 
the extrusive sheets, in the anterior ridge of Lamentation Mountain ; 
the base of an extrusive sheet, at Hartford; the top of an extrusive 
sheet in Saltonstall Mountain ; and extrusions of complex structure at 
Meriden and Tariffville. 
Roaring Brook, Gaylord’s Mountain. Locality 3. — On entering the 
ravine of Roaring brook from the drift plain at the eastern foot of Gay- 
lord’s Mountain, ontcrops of sandstone are soon encountered with dip of 
40° to the eastward. These are followed for several hundred feet up 
stream until the rock in the stream bed is found to consist of fine-grained 
trap, the line of contact having been passed unnoticed. A little search 
is needed to discover it, but-when once made out it can be followed 
with some distinctness. In a general way, the trap sheet thus disclosed 
lies parallel with the beds above it, but on tracing its surface up the ra- 
vine, it is seen to depart significantly from perfect parallelism and comes 
in contact successively with different beds. Moreover, it gives forth 
very distinct branches or leaders (Fig. 12), one of which extends for 
twenty feet into the overlying strata. The margins of these offshoots, 
as well as the edge of the sheet itself, are tolerably even, in marked con- 
trast with the excessive irregularity of the upper surface of the trap 
sheets of the eastern ranges. The overlying beds give not the least 
sign of trap fragments which so generally characterize the beds lying on 
the back of the eastern sheets. Taking all these features together, and 
placing them in contrast with those of the sheets on the eastern side of 
the valley, there can be no question that their consistent differences 
are due to some fundamental difference in the manner of eruption of 
the lava. We are forced to the conclusion, that the western sheet has 
been driven in between the previously deposited beds of sandstone and 
shale, while the others have been poured out on the surface of certain 
beds, and afterwards buried under others of later date. Study with the 
microscope confirms this conclusion. The trap of West Rock, a con- 
tinuation of Gaylord’s Mountain to the south, has been described _petro- 
ae 
