498 PROCEEDINGS OF TPIE NEW YORK MEETING 



Tlie following papers were all read by title : 



ROCKY MOUNTAINS OF MONTANA 

 BY BAILEY WILLIS 



ORIGIN OF SOME ARCHEAN CONGLOMERATES 

 BY A. E. BARLOW 



GEOLOGY OF THE CRYSTALLINE ROCKS OF MANHATTAN ISLAND AND VICINITY 

 BY FREDERICK J. H. MERRILL 



ORIGIN OF THE HIGHLAND GORGE OF THE HUDSON RIVER 

 BY FREDERICK J. H. MERRILL 



[Abstract^ 



The object of this paper is to call attention to some facts of geologic structure 

 which have had a very important influence on the course of the Hudson river and 

 the location of its gorge through the i)re-Cambrian highlands of Putnam and Orange 

 counties, New York. 



Tliis gorge has been for many year^ a subject of interest to geologists, and vari- 

 ous theories have been advanced concerning its origin. The most prominent of 

 these was that the river had followed an old fault line, erosion having been guided 

 by a line of displaceinent. 



Careful examination of the gorge and the adjacent territory shows that no dis- 

 placement has occurred and that no fault is there, but stratigraphic study of the 

 region has recently brought to light some facts which aid materially in assigning a 

 reason for the course taken by the river through the area of crystalline rocks under 

 consideration. 



The central portion of the highland gorge, about 7 miles in length, extending 

 from Cold Spring to Anthonys Nose, has a direction about north 30 degrees east, 

 following the general strike of the gneisses which form its sides. These rocks are 

 very distinct in character from the massive granites which form the highland 

 mountains, being quite schistose in structure, and include, at a number of points 

 along the east shore of the river, small areas of highly crystalline limestone. The 

 river in this part of the gorge is about half a mile wide. All evidence of the char- 

 acter of the rocks which form its bottom is wanting, and we are obliged to go north- 

 ward along the line of strike to determine their probable character. As may be 

 seen from an inspection of the West l^oint topographic sheet, from Cold Spring 

 northeastward extends a continuation of the valley occupied by the river, which, 

 about 8 miles from Cold Spring, opens into the Paleozoic plain of southern Dutchess 

 county. Through this valley the Trenton-Calciferous limestone of the latter region 

 can be traced for some distance southward in a closely pressed synclinal fold, the 

 pale blue, fine-grained limestone of Fishkill being succeeded farther southwest, 

 near Cold Spring, by a crystalline limestone which is apparently, in stratigraphic 

 continuity with the former, but which, by metamorphism, has become vastly 

 changed in its condition. 



This crystalline limestone is inclosed by gneisses similar in character to those 



