FIFTH REPORT OF THE DIRECTOR 



Natural Bridge it reappears, flows a short 

 distance upon Lowville beds and disap- 

 pears again under Black River limestone, 

 not to reappear for another half mile. 

 This last half mile is the most important g 

 for the understanding of the process which 

 produced the inlier farther up. The course 

 of the river can here be followed through 

 the woods by a distinct depression that is 

 covered with large, variously tilted Black 

 River slabs and partly bounded on the 

 sides by Black River cliffs. It is here 

 manifest that the Black River strata as a 

 whole have been sinking down along the 

 river as in a graben, being eaten away 

 underneath by the dissolving water. 

 Finally, the blocks become so small 

 that freshets are able to remove them 

 entirely and the river again flows in 

 the open and on the underlying Lowville 

 beds. While it is quite apparent that this 

 and other inliers of the same kind wander 

 upward, after they are started, by the 

 waterfall at the upper end, the original 

 cause of the phenomenon is quite clearly 

 the water that along the joints, which are 

 here strongly developed, passes between 

 and under the Black River blocks until it 

 reaches the harder and less soluble Low- 

 ville beds. The fall at the upper end is 

 to all appearances a secondary develop- 

 ment. 



It is obvious that this group of inliers 

 is essentially a Karst phenomenon and that 

 these inliers correspond to the " Dolinen," 

 so well known in the Karst plateau of Aus- 

 tria. We must, therefore, expect to find 

 other examples in the limestone regions of 

 the State. The Helderberg plateau pre- 

 sents a number of instances of depressions 

 or sink holes in the limestones through 

 which the underlying rocks appear. Most 



