National Geographic : 1894 Mar 17
24 N. H. Darton-ShawangunkMountain. 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 grit 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 valley 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.
1894 Apr 25
1894 Feb 14