Hobbs — Features Formed at the Time of Earthquakes. 251 



bottom. In one part of the shore, however, the plugs have been 

 left standing, each in its circular pit, some 4 or 5 feet above the 

 level of the surrounding rock ; and the foreshore here presents a 

 most extraordinary appearance, great masses suggestive of gigan- 

 tic fossil corals, or of the Paramoudras of the Chalk, standing up 

 from the rocky ledges, while others, torn out by the sea, lie pros- 

 trate in all directions." (See fig. 5.) 



The limestone at the locality is overlaid by about two feet of 

 sandstone with which the sandstone material of the pipes is 

 continuous though with no sign Q 



of collapse in the bed of sand- 

 stone (figs. 3,4). In fact, in most 

 instances the surface of the sand- 

 stone is gently domed upward 

 above the pipes and occasionally 

 has also a domed crack as well. 

 Within the pipe the bedding of 

 the sandstone sags downward and 

 a concentric structure is clearly 

 revealed by the brown weathering. 

 There is, moreover, a tendency to 

 radial jointing within the plugs. 

 The enclosing limestone of the 

 plugs is full of cracks at its upper FlG> 3 Sanclst0 ne pipes in 

 surface and these cracks are filled Carboniferous limestone, East 

 with sandstone. The pipes belong Anglesey (after Greenly), a, 

 ^ fh™„ ^ff OMn + T,nX^, ™-+M« cherty limestone ; [3, sandstone ; 



to three different horizons within 



y, cherty limestone. 



the same formation, and with much 

 probability represent fossil sand-blows like those described 

 from near New Madrid. Structures of a similar character, 

 the writer is informed by Professor A. H. Purdue, are found 

 in the Ozark mountains of Arkansas. 



Whereas during the New Madrid earthquake certain of the 

 fissures opened spouted the sand and water only locally to 

 build up cones; from others the same materials welled out 

 throughout the entire length of the fissures so as to produce 

 broad blankets of quicksand. Just as the sandstone pipes of 

 Anglesey illustrate the indurated relic of the one phenomenon, 

 so do the sandstone dikes described by Diller,"* Hay,f Crosby, J 

 and Case§ the other. Without exception these authors have 



*J. S. Diller, Sandstone dikes, Bull. Geol. Soc. Am., vol. i, pp. 411-442, 

 pis. 6-8. 1889. 



f Robert Hay, Sandstone dikes in northwestern Nebraska, ibid., vol. iii. 

 pp. 50-55, 1892. 



% W. O. Crosby, Sandstone dikes accompanying the Great Fault of Ute 

 Pass, Colorado, Bull. Essex Inst., vol. xxvii, pp. 118-147, 1895. 



§E. C. Case, On the mud and sand dikes of the White River Miocene, Am. 

 Geol., vol. xv, pp. 248-254, 1895. 



