I20 NEW YORK STATE MUSEUM 



the filled fissure is scarcely anywhere over 2 feet, but the lateral 

 offshoots extend many feet into the walls of Manlius limestone. 

 These offshoots or rootlets of the dike are irregular, commonly nar- 

 row, and often appear as isolated cjuartz masses in the Manlius or 

 the waterlime rock, the connection with the main dike not being- 

 always discernible. Such masses of quartz sandstone have been 

 traced for more than 30 feet from the dike. The irregularity of the 

 walls of the fissure is very pronounced. Angular masses of lime- 

 stone project into the cjuartz rock, while narrow tongues of sand- 

 stone everywhere enter the limestone. Extensive brecciation of the 

 limestone has occurred along the margin, and the sandstone there 

 is filled with angular fragments of the limestone, which show no 

 traces of solution or wear by running water. These limestone frag- 

 ments are themselves frequently injected with tongues of the quartz 

 sand. Microscopic examination shows evidence of a certain amount 

 of shearing along the margin of the dike, accompanied by a pul- 

 verizing or trituration of the limestone, and followed by reconsoli- 

 dation. These and other features point to a cataclysmic origin of 

 the fissure which contains the dike and a more or less violent in- 

 jection of the sand. The fissure must have been formed and filled 

 before the deposition of the Onondaga limestone and while the Man- 

 lius limestone was covered by a stratum of unconsolidated sand. 

 The formation of the fissure and the injection of the sand into it 

 from above must have occurred simultaneously; for this appears 

 the only way to account for the inclusion of large fragments, or 

 " horses ", of the wall rock in the loose sand, and the injection of 

 the sand into all the cracks and crevices. It seems probable that 

 the .fissure records an earthquake shock during the period interven- 

 ing between the close of the Siluric age and the deposition of the 

 Devonic limestones. This is borne out by the occurrence of numer- 

 ous small faults or displacements in the underlying strata of water- 

 lime. 



Devonic strata 



The Lower Devonic is represented in the Niagara region by the 

 thin beds of shale and sandstone before mentioned as occupying 

 erosion hollows in the Manlius limestone. These are perhaps the 



