﻿GEOLOGY OF THOUSAND ISLANDS REGION II3 



and to a certain extent at least is due to the pivotal situation of the 

 region with respect to the early Paleozoic warpings, as has already 

 been shown. In general the rocks lie, in nearly flat attitude, on the 

 worn surface of the sharply folded Precambric rocks. Over most 

 of the district a low, southwesterly dip prevails; locally, however, 

 the dip steepens to 5° or more, and dips occur in all compass direc- 

 tions. A strong westerly dip in the rocks along the Black river 

 just above the bridge at Brownville is well shown in plate 28, and 

 the dip is to the north, into the bank, as well, rock layers on the 

 south side of the river lying some 10 feet higher than their 

 equivalents on the north bank. In plate 24 a rather steep north- 

 erly dip in the Black River limestone at Watertown is shown, and 

 in plate 21 a similar easterly dip in the same formation at another 

 locality. These are samples of what is a matter of common oc- 

 currence all over the district. The areal mapping plainly brings 

 out the presence of a series of folds which trend somewhat to the 

 east of north. It also shows that the present stream valleys of the 

 region in large part trend with these folds and chiefly follow the 

 anticlines, while the synclines constitute the higher ground be- 

 tween. 1 Examples are the valleys running south from Theresa and 

 from Evans Mills on the Theresa sheet; the French creek valley 

 and the Chaumont valley on the Clayton sheet ; and the Clear lake- 

 Butterfield lake-Black creek valley on the Alexandria sheet ; but 

 there are many others of minor importance. 



In addition to these nearly north-south folds there is a second 

 set, about at right angles to the first, trending somewhat to the 

 north of west, in parallelism with the Frontenac axis which is 

 itself a fold of this group, the axial and most prominent one. 

 Though mostly of minor importance, these folds are likely earlier 

 than the others, and in part at least owe their existence to the 

 warpings and tiltings of the region in early Paleozoic times, when 

 it oscillated up and down, with tipping now to the east and now 

 to the west. The Frontenac axis appears to be the major warp 

 of this series, and the others are minor corrugations, grouped 

 about it and diminishing in importance with recession from it. 



/An anticline is the upward folding of rock layers into a long and rela- 

 tively narrow arch; a syncline, the downfolding into a similar trough. 

 Where erosion has removed the upper portion of such folds a worn off 

 anticline is readily recognized on an areal map since it will show an older 

 rock centrally, followed by successively younger rocks in the same order On 

 each side; while an eroded syncline -will show a youneer rock in the center, 

 followed by successively older rocks on each side. Thus the French creek 

 valley, south of Clayton, shows Precambric rocks centrally, adjoined py 

 Potsdam on each side, Potsdam adjoined by Theresa and that by Pamelia 

 kmestone, and the structure there is anticlinal. 



