116 BULLETIN OF THE 



4. — Special Accouuts of the more important Localities. 



The following more extended descriptious 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. AVe thus present examples of what we interpret as an in- 

 trusive sheet at Koaring Brook, on Gaylord's Mountain ; a bed of vol- 

 canic ashes and bombs, presumably near the locus of eruption of one of 

 the cxtiusive 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, GaylorcVs Monntain. Locality 3. — On entering the 

 ravine of Roaring Brook from the drift plain at the eastern foot of Gay- 

 lord's Mountain, outcrops of sandstone are soon encountered with dip of 

 40° to the eastwai'd. These ai-e 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 

 Avitb some distinctness. In a gcnei'al way, the trap sheet thus disclosed 

 lies parallel with the beds above it, but on tracing its surface up the I'a- 

 vine, it is seen to depart significantly from perfect parallelism and comes 

 in contact successively with dilTerent beds. jNloreover, 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 oiFshoots, 

 as well as the edge of the sheet itself, ai'e tolerabl}' even, in marked con- 

 trast with the excessive irrcgulai-ity of the upper surface of the trap 

 sheets of the eastern langes. 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 tiie sheets on the eastern side of 

 the valley, there can be no question that their consistent differences 

 are due to some fundamental ditlerence in the manner of eruption of 

 the lava. We are forced to the conclusion, that the Avesteru 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 latei- 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- 



