Topograpliical Features of the New Haven region. 61 



pears to have terminaterl southward the basin of Pine-Marsh Creek, 

 might under other circumstances have made basins for lakes. Lake Sal- 

 tonstall, four miles east of New Haven, probably owes its existence to 

 this action. The lake is 3.^ miles long and has an average breadth of 

 a third of a mile. The basin is scooped out of a very soft, crumbl ing 

 shaly sandstone, and lies between two bow-shaped trap dikes, three- 

 fourths of a mile apart, whose average trend is north-northeast. Its 

 depth is stated at 112 feet ; and since its surface is only half a dozen 

 feet above high-tide level, the bottom is more than 100 feet below 

 that level. At the present outlet the waters flow over solid trap at a 

 low cut in the western trap ridge, so that the basin is here rock-bound 

 on the south. The stream from the lake (called Stoney River, but 

 properly the lower part of Farm River), flows for its last mile be- 

 tween granite shores and has in some places a rocky bottom. Thus 

 there is a granite as well as a trap barrier between the lake and the 

 sea, and the depression it occupies is a true basin. We may believe 

 therefore that the long narrow basin occupied by the lake is an excava- 

 tion made in the soft sandstone by the ploughing glacier, and that it 

 was not continued to the sea because the ploughshare was lifted out of 

 its trench by the hard unyielding rock before it. 



Height of the Land in the Glacial era. — With regard to the 

 height of this portion of Connecticut above the sea in the Glacial era 

 we have as yet few facts for definite conclusions. 



a. In sinking an artesian well on Green st., 120 yards from the 

 harbor, a bed of fine clay 14 feet thick was struck at a depth of 140 

 feet, or 126 feet below mean tide level. Above this clay there 

 were the ordinary sand or gravel deposits of the New Haven plain. 

 The clay bed was evidently a mud deposit made in the harbor as it 

 existed immediately before the deposition of the sand ; and as the 

 sand beds of the New Haven plain date from the era following the 

 Glacial, the harbor very probably was that of the Glacial era. If the 

 land then stood 125 feet above the present level, the mud bed would 

 have lain just at the water's surface, like those of the present day. 

 The evidence as to the level of the land in the Glacial era is uncer- 

 tain; still it affords a presum2:)tion that it was at least 125 feet higher 

 than now. No clay has hitherto been found in any other part of the 

 New Haven plain. 



h. Near Stoney Creek, eleven miles east of New Haven, on Smith's 

 Island, one of the " Thimbles," there are two pot holes in the hard 

 gneiss rock; oiie of them is 1\ feet deep, and 3 in diameter, and the 

 other 3 feet deep and 10 inches across. They are situated within a 



