﻿[08 NEW YORK SPATE MUSEUM 



faces therefore the joints ordinarily divide the exposure into rhom- 

 boidal, rather than rectangular blocks. In plates 15, 20 and 23 

 joints are well shown. 



The limestones of the district exhibit, in general, more abundant, 

 more regular, and more clean cut joints than does the Potsdam sand- 

 stone. The limestones moreover are all somewhat soluble in rain 

 water and underground water, the Black River and some of the 

 Lovvville beds being preeminent in this respect. The glacial depos- 

 its over the district are in rather scant amount, there being much 

 bare rock exposed, and much more only thinly coated with soil. 

 On the bared limestone surfaces the widening of the joint cracks 

 produced by slow solvent action of rain water which passes under- 

 ground along them, is magnificently shown [pi. 26, 27], most 

 impressively perhaps in the Black River beds but almost equally 

 well in the upper Lowville. In many fields which might other- 

 wise be available for pasturage, the cattle must be carefully ex- 

 cluded, otherwise they fall into, and become tightly wedged in these 

 gaping fissures. During our field work we came by chance upon 

 a poor, stray cow in such plight in the vicinity of Limerick, tightly 

 wedged in a fissure of sufficient size so that the animal's back was 

 well below the ground surface. 



Down these widened joint cracks also the streams go underground, 

 so that surface streams are infrequent in the Black River and upper 

 Lowville districts. Beneath, this downward tendency is checked by 

 the less soluble character of the remainder of the Lowville, on the 

 upper surface of which these waters run along, eating away under- 

 ground channels of considerable size in the soluble layers just above. 

 In their early stages these channels are thoroughly roofed over, but 

 as time goes on the roof tends to disappear, either by caving in be- 

 cause of lack of support by the widened channel underneath, or by 

 slow dissolving away of the rocks above, thus bringing daylight 

 down to the upper part of the tunnel. The matter will receive 

 more detailed discussion when treating of the general drainage, but 

 the details of the process and its varying stages are most excel- 

 lently illustrated in the region [pi. 35-38]. While it is in many 

 cases impossible to distinguish between preglacial and postglacial 

 solution, it is nevertheless clear that much of this limestone removal 

 is postglacial. 



Folds 



The rocks of the district exhibit various degrees of folding. The 

 Grenville sediments are closely and intricately folded ; the Paleozoic 

 rocks show slight folding of Paleozoic date; and the same rocks 



