MARGINAL GLACIAL DRAINAGE FEATURES 533 



sharply trimmed. In the lower end are several hummocks, apparently 

 of a morainic nature. This older channel was occupied during the 

 retreat of the last ice-sheet by a small stream which formed a second 

 channel twenty or thirty feet wide within the older one, which has a 

 width of about 125 feet. The smaller channel has distinctly trimmed 

 though low banks, and a characteristically swampy bottom. At its 

 upper end the older channel is buried in a gently undulating moraine 

 in which the smaller and later stream seems to have originated. 



TYPE II. SUBMARGINAL 



Cayuta Gorge channel. — An excellent example of this type is 

 Cayuta Gorge at the outlet of Cayuta Lake (Fig. 4; Ithaca sheet, 

 U. S. G. S.). The lake lies in a broad, mature valley trending a little 

 south of southwest. At its southern end a glacial deposit, about 

 forty feet in average height stretching across the valley, forms the 

 dam to which the lake owes its origin. In one place on the west side 

 of the valley near the schoolhouse the top of this barrier is less than 

 twenty feet, and probably not more than ten feet above lake level. 

 Through this gap to the south is free communication with Catlin Mill 

 Creek, and thence with Seneca valley; yet the lake waters, instead 

 of finding an outlet through this low pass, turn eastward and escape 

 through a rock gorge cut to a depth of over three hundred feet through 

 the hill bordering Cayuta valley on the east (Fig. 4). That this 

 outlet is no normal valley, is shown by its almost perpendicular rock 

 sides and its lack of harmony with the surrounding topography. 

 Clearly nothing but the intervention of a glacier could have produced 

 such an abnormal drainage condition in a region of horizontal and 

 comparatively homogeneous rocks. 



As is show by a map of the moraines of this region,' a lobe of 

 ice from the great Seneca valley tongue lay for a long time across the 

 lower end of Cayuta Lake valley. Such an ice-lobe would obstruct the 

 normal drainage and cause the water to escape over the lowest point 

 in the valley side. This, in this case, clearly must have been the site 

 of the present gorge. In order to permit the cutting of so profound a 

 gorge, the glacier must have stood nearly stationary for a long time. 

 It might have been melting away as fast as the gorge was being cut 



I Tarr, Bui. Geol. Soc. Am., Vol. XVI, 1905, pp. 215-28. 



