412 The American Naturalist. [May, 
specimens of Carcharodon, found in the Red Crag of England. (Geog. 
Journ., Jan., 1894.) 
Intrusive Sandstone Dikes in Granite.—During the summer 
of 1893, a peculiar sandstone rock composed of worn quartz grains was 
discovered in the neighborhood of Pikes Peak in the western side of the 
narrow Manitou park basin of sedimentary rocks. This rock occurs 
as the filling of an extensive system of fissures in granite under circum- 
stances indicating that the sand was forced into the fissures under great 
pressure. Mr. Whitman Cross discusses the origin of these Dikes with- 
out, however, coming to any definite conclusion. So far as he is aware 
no other occurrence of sandstone dikes in granite has ever been de- 
. scribed. They may be compared with the remarkable occurrences mM 
California described by Diller. These latter, however, were in $ ales 
of a great sedimentary complex of Cretaceous age, and they were 
parallel to a system of jointing planes in the strata. Moreover, Diller 
noted that below the horizons occupied by the dikes there occurred 
sandstone strata of a composition identical with that of the dike-rocks. 
The very plausible theory presented by Diller was that the fissures re- 
presented by the dikes were formed by earthquake shock, and that the 
sand wasinjected as quick-sand into the fissures under hydrostati¢ peo 
ure from unconsolidated water-bearing sand layers below. 
The Colorado dikes are more difficult to explain than those of Cal- 
ifornia in that the known facts do not indicate the source of the et 
yet the physical and mechanical facts do seem to show that the fissures 
of this dike complex were filled by a fine quick-sand injected ra 
source containing a large amount of homogeneous material. Ont 
one hand, it is impossible to suppose that such a system of fissures 
large and small, with their many intersections, could remain open tobe 
filled by any slow process, and, on the other hand, it is equally TE 
possible to believe that the uniformity and purity of the mateni 
ing the fissures, varying from mere films on cleavage planes i 
clase grains in the granite to dikes several hundred yards 1m "E 
could have resulted from infiltration. ‘acent 
It has been stated above that the belt of observed dikes lies adjacel 
and parallel to the Manitou park basin of sedimentary r ocks, the ee 
cipal element in which is the red sandstones and grits of the Paf and 
ferus (?) or Trias (?). These beds are, however, of much oa 
more heterogeneous character than the dike-rock, and the o 
made do not suggest that the proximity is anything more a ci 
! Sandstone Dikes, J. S. Diller: Bull, Geol. Soc. Am., Vol. I, 1889. 
A 
