792 PRINCIPLES OF STRATIGRAPHY 



such erosion along joint cracks may be seen in the Tertiary sand- 

 stone of Monument Park, Colorado, where in the ledges the begin- 

 nings of this erosion work are seen, while scattered through the park 

 are numerous isolated stone pillars, generally capped by a fer- 

 ruginous block of greater resistance, the last remnants of an ex- 

 tensive formation which formerly covered the entire region. 



13. Earthquake Fissures. A well-known ])henomenon accom- 

 panying more or less violent seismic disturbances is the opening of 

 fissures in the rock by the tearing asunder of the mass. Such fis- 

 sures may remain open or be filled subsequently by the washing into 

 them of surface material, or they may be filled at the time of forma- 

 tion by material violently injected into them from above. Recent 

 fissures have been described by Whimper and others. (See Chapter 

 XXIII.) Examples of such fissures are sometimes found in the 

 fossil state. Thus the Upper Siluric limestones and dolomites of 

 western New York and Ontario are traversed by vertical fissures, 

 which show evidence of violent disruption, and into these fissures 

 sands representing the Oriskany period were injected. These sands 

 apparently rested on the old erosion surface of the Siluric limestone 

 before the shock came. The shock was a pre-Middle Devonic one, 

 for Middle Devonic (Onondaga) strata rest upon this mass without 

 showing any evidence of being affected by the shock. One of the 

 best examples of this group has been described from the cement 

 quarries of North Buffalo. 



"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 trun- 

 cated end and on the limestones flanking it. The Onondaga lime- 

 stone is entirely unaffected by the dike, being evidently deposited 

 after the formation and truncation of this remarkable mass of sand- 

 stone. The width of the fissure is scarcely anywhere over 2 feet, 

 but lateral offshoots extend for many feet into the walls of Bull- 

 head [and Bertie] limestone. These offshoots or rootlets of the 

 dike are irregular, commonly narrow, and often appear as isolated 

 quartz masses in the Bullhead or Waterlimes, the connection with 

 the main dike not being always observable. Such masses of sand- 

 stone 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 mar- 



