﻿GEOLOGY OF THOUSAND ISLANDS REGION 1 43 



relation as that which initiated the Black valley. The only features 

 which are not in harmony with the above theory are the southward 

 course of a section of the Indian river, above Evans Mills, and of 

 the Oswegatehie above Oxbow. These are probably due to glacial di- 

 version, similar to that of the Black below Great Bend, but for 

 better knowledge we must await the topographic sheets. 



Professor Cushing suggests that north from Felts Mills the pre- 

 glacial divide might have swung west from the present course, pass- 

 ing south of Perch lake, through Depauville and south of St Law- 

 rence corners. The wider valley of the Chaumont north of Depau- 

 ville and the northward course of French creek favor this view. 

 It is quite possible that Prewisconsin glacial erosion has caused a 

 northward migration of the portion of the divide that was trans- 

 verse to the ice flow, but the latest ice work seems to have been 

 too weak. We may not appeal to forced stream flow during the 

 last ice recession, as the region was- then buried under Iroquois 

 waters. The northward uptilting of the area tends of course to 

 divert sluggish drainage into southward flow, but alone this could 

 not be a very effective factor. 



Passing now to certain specific data and features connected with 

 very recent history, the reader should note again the intimate rela- 

 tion and parallelism of Black river to its northward flowing neigh- 

 bors [pi. 43], after which a glance at plate 44 will show the cause 

 of the separation and the character of the barrier. At Great Bend 

 and Felts Mills the river has cut into the south side of its own 

 delta, that was built in Lake Iroquois. Along much of that stretch 

 rock is seen in the bed of the river, beneath the steep wall of the 

 delta deposits. North of the delta the ground is 100 feet or more 

 lower than the river, and all draining northward. At Felts Mills 

 the river has an altitude of 580 feet, while only iy 2 miles north, 

 and simply across the delta divide, is Pleasant creek, a tributary 

 of Indian river, at only 520 feet altitude. The fall from Black 

 river to Indian river by Pleasant creek is 200 feet in about 6 miles. 

 Further up stream, at Great Bend the river has a large meander in 

 the delta and the facility for northward flow may be even better 

 than at Felts Mills, but the topographic survey has not covered the 

 district. 



The suggestion is natural that possibly a rock barrier is buried 

 under the delta, which would be an effective barrier to north escape 

 of the river if the delta were removed. Fortunately we have 

 specific data. Mr F. A. Hinds, the well known hydraulic engineer 

 of Watertown, has pointed out the important fact that the drainage 



