﻿•GEOLOGY OF THOUSAND ISLANDS REGION 157 



smooth clay fillings, as meadows or swamps between the rock bluffs 

 or among the rock knobs, make striking contrast [pi. 29]. 



The clay is evidently the rock flour of the glacial mill, sifted by 

 the standing waters. Its glacial relationship is shown by the fact 

 that in some localities it shades into ordinary clayey till ; by its in- 

 clusion of boulders and cobbles, probably ice rafted; and by its 

 composition which is decidedly calcareous. 



In many exposures the clay rests directly on glaciated rock [pi. 

 57] with no mass or visible layer of till or stones intervening. In 

 the gullies or storm-wash hollows a few cobbles or boulders -are 

 commonly found, derived from the mass of the deposit, but they 

 do not seem perceptibly more common at the base. The bed of 

 the creek where plate 57 was taken was filled with cobbles from the 

 clay ravine. At the top of this section the lamination was destroyed, 

 but the crushing appears to be very localized, and has rarely been 

 noted elsewhere. However, the structure does not often appear, as 

 the exposed clay quickly loses its lamination and forms a rough, 

 crackled skin over the slope, as shown in plate 58. It is only where 

 the clays are freshly exposed that the lamination becomes evident. 



In plate 58 the numerous white fragments scattered over the 

 slope are calcareous concretions, discoid or irregular in form. Evi- 

 dently they represent concentration of the lime that was originally 

 disseminated in the deposit, but the clay still retains enough of the 

 carbonate to effervesce very freely in weak acid. The latter is 

 true of all the clays tested, except in some cases the topping lay- 

 ers, 1 or 2 feet thickness. The lack of carbonate at the surface 

 may be due to postglacial leaching, and perhaps to original lack of 

 carbonate since the latest beds may have been deposited from well 

 washed material, the ice being far removed to the northward. 



Some sections do not contain the lime concretions. This is the 

 case with a great exposure iy 2 miles east of Clayton where the 

 river has undercut the bank, giving a section 15 to 18 feet high. 

 The lower part is beautifully laminated, the upper part with older 

 exposure showing the characteristic mottled or crackled skin and 

 some small lime particles. The east end of the clay section exhibits 

 some crumpling of the beds. All these clays effervesce freely. 



The volume of this clay over the area increases southward, over 

 the limestones, but the total seems excessive in proportion to the 

 scanty drift of other materials. It is possible that the genesis and 

 history of the clay is more complex than would at first appear. 

 Apparently it is all Postwisconsin, for if it were partly the deposit 

 of ice of earlier invasion we should expect to find the deeper and 



