SANDSTONE DIKES; CRATERLETS 885 



time, becoming gradually filled up by debris wbicli falls in from 

 above, or is wasbed into tbem. Sucb is tbe case in several vertical 

 fault fissures at Meriden, Connecticut, wbicb bave been filled by 

 infiltration of trap fragments and sandstone from above. (Davis, 

 in Diller-8:7^i'.) 



Davis says: "Tbese fractures traverse a sbeet of lava and 

 are cbiefly filled witb angular trap-fragments, Init tbe interstices are 

 occupied with sandstone, not in fragments as if it had fallen in 

 with the pieces of trap, but in a close-fitting mass, as if it had 

 settled down in the form of separate particles derived from the 

 sandstone originally overlying the trap sheet, thus, in a general way, 

 taking a structure conformable to tbe blocks of trap that it sur- 

 rounds, but showing also a tendency to a transverse or horizontal 

 stratification. It seems probable that these fissures were filled 

 gradually by infiltration from above . . ." 



In some cases, however, such fissures are filled at the time of 

 their formation by sand violently injected into them either from 

 below or above. Cases of mud and sand welling up from volcanic 

 fissures have been frequently observed, and seem to be a general 

 accompaniment of such fissures near the surface. In some cases, 

 as in the earthquake of Chemakha, Turkestan (Feb. 12, 1902), "salty 

 plastic mud exuded from the open faults and built up high hillocks 

 of the pasty material, which were surmounted by craters" (Hobbs- 

 iS:iJ4). Subsequent movement along the plane caused a dis- 

 placement in these "mud volcanoes" to the extent of 1.5 meters 

 in some cases. Sand and mud injections of this type are known 

 from older geological formations, where they form sandstone dikes. 

 Thus Newsom iSS-^SS) describes a sandstone dike 2^ to 5 feet 

 wide from California, in which the upward bending of the shales 

 on either side is regarded as proving its injection from below. 

 Others from the same general region are also described. Violent 

 injection into an earthquake fissure of loose sand, which covered the 

 surface of the rock, seems to have taken place in the case of the 

 Lower Devonic sandstone dike (injected into Upper Siluric strata) 

 at Buffalo, as described in a preceding chapter. For a general 

 summary of sandstone dikes with references to the literature, the 

 student is referred to Newsom's article (33). 



Craterlcts. Analogous to the injected sandstone dikes are the 

 craterlets formed by sand and mud ejected with water from earth- 

 quake fissures. One such has already been noted in connection 

 with the Chemakha earthquake. Others were noted in the Charles- 

 ton earthquake of 1886. Some of these which were aligned along 

 fissures measured 20 feet in diameter, while the water and sand 



