. Bulletin of the Geological Society of America. Geology. 358 A. \V. GRABAU—SILURO—DKVONIC CONTACT IN NEW Y<)KK examination at a subsequent date showed this so-called pocket to be a residuary dike of sandstone, formed by the filling of a fissure which penetrated the entire thickness of the Bullhead limestone and entered the Rondout Waterlime from 2 to 3 feet. The total depth of the fissure, as now exposed with its filling of sandstone, is in the neighborhood of 10 feet. The dike is squarely cut off at the top. where the Onondaga limestone rests on its truncated end and on the limestones fla
. Bulletin of the Geological Society of America. Geology. 358 A. \V. GRABAU—SILURO—DKVONIC CONTACT IN NEW Y<)KK examination at a subsequent date showed this so-called pocket to be a residuary dike of sandstone, formed by the filling of a fissure which penetrated the entire thickness of the Bullhead limestone and entered the Rondout Waterlime from 2 to 3 feet. The total depth of the fissure, as now exposed with its filling of sandstone, is in the neighborhood of 10 feet. The dike is squarely cut off at the top. where the Onondaga limestone rests on its truncated end and on the limestones flanking it. The Onondaga limestone is entirely unaffected by the dike, being evi- dently deposited after the formation and truncation of this remarkable mass of sandstone. The width of the fissure is scarcely anywhere over 2 feet, but lateral offshoots extend for many feet into the walls of Bull- head limestone. These offshoots or rootlets of the dike are irregular, commonly narrow, and often appear as isolated quartz masses in the Bullhead or the Waterlime, the connection with the main dike not being. FlGTJre ti.—Fragment of Rock from Margin of Sandstone Dike, Show in- angular pieces of limestone included in the sandstone and injected by tongues of the sandstone (natural size). always observable. Such masses of quartz sandstone have been noted at a distance of 20 or 30 feet from the main dike. They are always small. The dike itself has been traced for more than 30 feet in an east-and-west direction in the sloping walls of the quarry. The walls of this ancient fissure are very irregular, angular masses of the limestone projecting into the quartz rock, while narrow tongues of sandstone everywhere enter the limestone. Extensive brecciation of the limestone has occurred along the margin, and the sandstone there is filled with angular frag- ments of the limestone, which show no traces of solution or wear by running water. These limestone fragments are themselves frequently inje
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