360 A. W. GRABAU — SILURO-DEVONIC CONTACT IN NKW YORK 



showing any secondary enlargement, thus indicating that they were in- 

 cluded before the consolidation of the sand in the fissure. The appear- 

 ance suggests a trituration of the limestone along the walls of the fissure 

 and the borders of the included fragments, the finely granulated lime- 

 stone mud being mixed with the coarser quartz grains, the whole con- 

 solidating without the formation of any but minute crystals of the 

 calcareous minerals. Frequently a considerable mass of the limestone 

 cement occurs between the grains of quartz, and in such cases crystals 

 of pure calcite or dolomite occur in the center of the cement. 



Sometimes sand grains are only partially surrounded by limestone, 

 the other portions showing an addition of secondary quartz. Occasion- 

 ally the interstices between adjoining sand grains are' completely filled 

 by new quartz of definite form and individualized. Along the contact 

 zones between sandstone and limestone, cavities occur in the latter rock, 

 completely filled with crystalline calcite, indicating a recrvstallization 

 after the disturbance which granulated the limestone. There are also 

 microscopic fissures in the limestone masses filled with crystalline cal- 

 cite. Along the sides of the dike, masses of limestone in long narrow 

 bands are not uncommon in the quartz rock. These commonly contain 

 rounded sand grains, and near their margins the grains of the dike are 

 surrounded and cemented by the limestone. They appear to represent 

 crushed masses of limestone, which were strung out parallel to the walls 

 of the fissure while the sand was in motion. Carbonaceous matter is 

 common in these limestone bands and the limestone adjoining the 

 quartz dike generally. It usually occurs in black specks, which are 

 numerous where the limestone shows evidence of crushing, but much 

 less common in the solid, unaltered limestone. Sometimes the quartz 

 grains of the dike near the margin are entirely surrounded by the car- 

 bonaceous matter, which in places constitutes the cement. 



All the features, macroscopic and microscopic, which accompany the 

 sandstone dike point to a cataclysmic origin of the fissure which con- 

 tains it and a more or less violent injection of the sand. Mere erosion 

 or widening of a joint fissure by solution will not account for the phe- 

 nomena observed. That the fissure was formed before the deposition of 

 the Onondaga limestone seems evident from the fact that this latter rock 

 is entirely unaffected. It seems also certain that the fissure was formed 

 after the deposition of a considerable mass of sand over the Manlius 

 limestone, and that the formation of the fissure and the injection of the 

 sand from above occurred simultaneously. In no other way can we 

 account for the inclusion of horses of the wall rock, often of consider- 

 able size, and the injection of the sand into all the fissures and crevices ; 

 nor can we readily explain on any other hypothesis the trituration of 



