58 J. D. Dana on the origin of some of the 



into a new arch by tins dike, losing in the encounter the red sandstone 

 from the back (or north side) of its head, down nearly one-third way 

 to its base. Either side of this dividing ridge the glaciei*, besides 

 abrading the general surface of the sandstone formation and thereby 

 preparing the rocky basement for the alluvial plains, was ploughing 

 out the river channels adjoining — that of the small Mill River on 

 the west, and that of the broad Quinnipiac on the east. It is a strong 

 confirmation of the view brought forward that the direction of the 

 Quinnipiac ridge, (as well as that of Sachem's ridge,) is S. 12° W. (true 

 course), thus coinciding with the average direction of the Connecti- 

 cut valley, and therefore with that of the movement in the glacier. 



The largest of the valleys in the Hamden portion of the New Ha- 

 ven region lies along side of the West Rock ridge, where the erosion 

 of the glacier, and of the waters flowing from them would have been 

 greatest in consequence of the height of the rock and its slopes, 

 and where, moreover, erosion from running waters has been going on 

 ever since from the streamlets that the rains and melting snows have 

 made over the long declivities. In this valley lie Wintergreen Lake 

 (due to a recent damming of one of the streams), and farther north 

 the sites of other " contemplated" lakes. 



This western part of Hamden is drained by Wilmot brook with its 

 tributaries, which flows through the gap between Pine Rock and 

 West Rock and soon after enters West River. The northern poi'tion 

 of the brook, which lies among the sandstone ridges, points southward 

 nearly toward the northern extremity of the Beaver Pond depression, 

 and approaches it within two-thirds of a mile. It might therefore be 

 queried whether Pine Rock had any effect toward dividing the excava- 

 ting action of the glacier on the north, like that from Mill Rock above 

 described. But there is this great difference in the two cases, that the 

 gap between Pine Rock and West Rock is very much broader than 

 the Whitney ville gap, being about a quarter of a mile across, and be- 

 sides there is no continuous pavement of trap at bottom. Moreover 

 Pine Rock has an oblique position with reference to West Rock, its 

 direction being E. 20"" N. true course, (about E. 12° N., compass 

 course,) and owing to the convergence of these two ridges and the 

 broad opening intermediate, and also to the S. 12° W. direction of the 

 glacier movement, the principal part of the excavating portion of the 

 glacier would naturally have passed between them, where Wilmot 

 brook has its actual course. 



Looking beyond the limits of the New Haven region, still other 

 examples of this north-and-south ridging of the soft sandstone occur. 



