II- J. S. DILLER — SANDSTONE DIKES 



of earthquakes natural phenomena which are by n<> moans ran- in Cali- 

 fornia. 



The geologic structure of the region is Buch as to render it especially 

 favorable for the production of sandstone dikes by means of earthquakes; 

 and the evidence appears to be conclusive thai these dikes record seismic 

 movement during tin- Tertiarv. 



DISCUSS Joy. 



Professor W. M. Davis. — In confirmation of Mr. Diller- suggestion that 

 detrital material supplied from above would take a horizontal stratification 

 as it settled into a fissure, I may make reference to the several vertical fault- 

 fractures in the city trap-quarry, at Meriden, Connecticut. These fractures 



traverse a sheet of lava and are chiefly filled with angular trap-fragments, 

 but the interstices are occupied with sandstone, not in fragments as if it had 

 fallen in with the pieces of trap, hut 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 -tincture con- 

 formable to the blocks of trap that it surrounds, hut showing also a tendency 

 to a transverse or horizontal stratification. It seems probable that thi 

 fissures were tilled gradually by infiltration from above, while those that 

 Mr. Diller describes were tilled suddenly by violent pressure from below. 



Professor 15. K. EMERSON: I wish to describe in a word an abnormal vein 

 tilling which, though occurring on a small scale as compared with the re- 

 markable cases ju-t described, may have some reaemblai in origin. The 



till in the Connecticut valley often requires blasting; and in a deep cellar 

 excavated in this way a great horizontal sheet ofsands nearly two feet thick 

 and above sixty feci long was exposed, covered by twelve to twenty feet of 



the m08l compact till and separated by two feet of the same firm till from a 

 heavier bed of buff sands, which was underlain by the till in great thick- 

 ness. The upper sheel of -ami had plainly beeri moved into its place a- a 

 frozen block separated from the lower sand, ami it terminated abruptly on 

 all -ides in the till. 



rting in the lower -ami. a fissure had formed, running up through the 

 two-foot band of till ami the -ami lied, and penetrating two or three feel 

 into the upper till, then tapering to a point. This fissure was filled with fine 

 clay, arranged in layers matching each other ami all parallel to the walls of 

 the fissure. It seems plain that the whole ma-- must have been renl by 



-•■in' -train due to the motion of the ice while it wa- itself frozen, and that 

 by hydrostatic pressure the fissure wa- tilled with mud or muddy water from 

 below, and that this occurred with several i n t • -rmi — ion- to effecl the band- 



milt of the vein. 



