188 GEOLOGY OF THE SECOND DISTRICT. 



means of a small stream in the west part of Chester, at a place known as the Natural bridge. 

 The water at this place pours through a limestone ridge, and is constantly wearing away the 

 rock, and increasing the extent of its underground passages. If, however, the country should 

 be but slightly upraised, these caves would still exist, but the present stream would flow in 

 another direction. But I leave many of these questions without attempting their solution. 

 We have not obtained all the facts necessary for their rational exposition. 



Waterfalls. 



I should pass the diversified phenomena of waterfalls, with only the slight notice I have 

 already given, were it not that they always possess more or less of a geological interest. A 

 cause truly geological is either immediately concerned in their production as an uplift, crossing 

 the water course ; or else they are formed by the kind or condition of the masses over which 

 the stream flows. We may go back one step further, and say that even the courses of rivers 

 are determined by geological causes. The valleys through which they flow, have been in 

 most cases determined by the action of those internal forces which have raised up the crust 

 of the earth by upheavals ; or, by lateral pressure, liave wrinkled or folded the strata in paral- 

 lel ranges, forming thereby troughs or gently sloping surfaces, down which the rivers fall as 

 upon an inclined plane. 



In Warren county, there are two falls well worthy of notice : that at Luzerne, called the 

 High falls of the Hudson, and Glen's falls, both of which I have had occasion to notice. 

 Neither of them are remarkably high, but they possess an interest aside from the space 

 through which the water is precipitated. The river, at the former of these falls, flows for a 

 mile through a gorge, at the junction of the Potsdam sandstone and gneiss. The force which 

 produced the uplift, appears to have acted mostly upon the gneiss, as the layers of the sand- 

 stone are but slightly disturbed. The dip of the gneiss is N. 20° E. ; and that of the 

 sandstone, N. 20° W. 



The Hudson river begins to fall rapidly just below the ferry at Jessup's landing, and flows 

 thus for tliree-fourths of a mile over a rocky bottom, till within about eighty yards of the 

 precipice : it is then driven through a narrow cleft, which is spamied by a thirteen foot plank, 

 which serves as a bridge for the passage of footmen. There are many, however, who prefer 

 walking half a mile, to crossing a bridge so narrow, and over a flood whose course is as swift 

 as a racehorse, and which soon takes its leap of sixty feet over a ledge of gneiss nearly per- 

 pendicular. This fall may be seen about two miles di-stant, on the road leading from Glen's- 

 Falls to Jessup's landing : it there appears like a bank of snow, and no one would suspect it 

 to be a waterfall. 



The descent over which the water falls, spreads out very wide ; and when the river is low, 

 numerous black rocks project upwards in the midst of the white foam of the cataract. The 

 great width to which the water spreads, injures the effect as a whole ; at least it appears lower 

 in consequence ; still, it is an imposing sight. Upon tlic cast side, the gneiss rises in a per- 

 pendicular bluff nearly one hundred feet high. This mural precipice extends for some dis- 



