24 N. H. Darton—Shawangunk Mountain. . 
features of its geology in Ulster county, and they were found to 
be of great interest. In this article there is presented a brief 
summary of the results of my observations, but in a report on 
the geology of Ulster county, now in preparation, there will be 
a somewhat more detailed description of the region. 
The structure of Shawangunk mountain in Ulster county is 
a particularly interesting illustration of close relation of rock 
texture to topography, for the presence of the mountain and its 
form are directly dependent on the structure of a relatively thin 
sheet of hard rock. In the accompanying stereogram (plate 
1) an attempt has been made to represent its physiographic 
character, and the structure is shown in the cross-section at the 
ends of blocks into which the supposed model is divided. The 
mountain consists of a widely extended sheet of Shawangunk 
erit lying on soft Hudson shales. This sheet lies in a gently 
westward-dipping monocline which is corrugated by a series of 
gentle longitudinal flexures. To the westward it dips beneath 
shales and limestones of the succeeding formations in the Ron- 
dout valley ; to the eastward it terminates in long lines of high 
precipices which surmount steep slopes of Hudson shales. Its 
anticlinals give rise to high ridges and wide plateaus ; its syncli- 
nals constitute in greater part the intervening depressions. In 
several portions of the mountain the grit has been eroded off 
the crests of the anticlinals and the underlying slates are bared. 
This is the case in a wide area southeast of Ellenville, in a long 
strip extending from near lake Mohonk nearly to Rosendale, in 
a small area east of Wawarsing, and in the top of the mountain 
north of lake Minnewaska. Mather has suggested that the great 
cliffs of the region are due to faults, but I find this is not the 
case. Only one fault was found, and this was a small over- 
thrust in the Rosendale region. There are many slight faults of 
a few inches or feet, but they appear to be entirely in the grit. 
The surface of Shawangunk mountain is nearly everywhere 
very rugged, and cliffs and rocky slopes abound. These consist 
of snow-white grits, more or less mantled with dark lichens, 
and are remarkably picturesque. There are many cataracts, 
several beautiful rock-bound lakes, and widely extended views 
of the Catskills to the westward and the Hudson yalley to the 
eastward. The ruggedness is due to the exceptional hardness 
of the grits, the softness of the underlying shales, and a ten- 
dency to vertical jointing which gives rise to cliffs and clefts, 
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