506 



PROCEEDINGS OF PHILADELPHIA MEETING. 



ratel}' three of the former head streams of the south branch of Schoharie creek, 

 but its gorge has not so deeply invaded the original depression. 



The geologic structure of the region is such as to facilitate stream-robbing by 

 streams cutting backward in the face of the mountain. The formations are alter- 

 nating beds of hard sandstone and soft red shales, whicli dip gently westward. A 

 stream flowing on a hard bed down the dip would erode very slowly, and this has 

 been the case with the branches of the Schoharie. They rise in an elevated por- 

 tion of the mountain and after the lirst mile or two flow slowly to the westward 

 and empty into the Mohawk river many miles to the northwestward. With streams 

 flowing out of the mountain to the eastward the conditions are very different. 

 Tidewater is onl}'^ a few miles away, which gives great declivity, and on the steep 

 mountain slope streams cutting back against the dip rapidly remove the red shales 

 and undermine the sandstones. The relations of these features are shown in the 

 following figure : 



tHALC 



Figure i. — Cross-sectioyi of Front of northern Portion of Catskill Mountains near Kaalcrs Kill 



Gorge. 



The rapidity of erosion which progresses under these conditions is strikingly 

 illustrated in the Kaaters kill and Plaaters kill gorges, where relatively small streams 

 are causing the rapid recession of falls and deepening of the valley. Great cham- 

 bers are rapidly excavated in the red shale beds, and although tlieir roofs are 

 usually of heavy beds of hard, cross-bedded sandstone, these soon fall as the under- 

 mining advances. The Kaaters kill falls, Haines falls and falls of the Plaaters kill 

 are high, pictur(.'S(iue falls, which exhibit great thicknesses of the alternating hard 

 and soft beds. The newness of the great gorges is very evi<lent, and it is a feature 

 strikingly in contrast witii the wide, elevated depressions of the Schoharie branches 

 which the enterprising Kaaters kill and Plaaters kill have invaded. 



It was at no tlistant date, geologically, when the two lakes west of the INIountain 

 House drained into the north branch of Schoharie creek along a dei)ression which 

 passed with gentle slope along by I) and E (see plate 23) and merged into the 

 present Schoharie dej)ression at the present divide, three-quarters of a mile west of 

 Haines falls. 



The history of the Plaaters kill invasion was quite similar and is, I think, clearly 

 indicated on the map. No doul)t originally there were high gaps in the Catskill 

 fi'ont where the Kaaters kill and Plaaters kill gorges now lie, which gave the in- 

 vaders advantage over the other streams which head against higher portions of the 

 front. These wind gai^s occur frequently throughout the Catskills and are related 

 to an earlier i:)hase in the topographic development of the mountains, which I will 

 not discuss here. There is strong suggestion of the former presence of a gap of thig 



