THE TRIASSIC PERIOD. 



5 



This is usually fine and of an earthy nature, and gives rise to mud 

 beds; or if there be abundant chert in the limestone, the insoluble 

 residue may be coarse, giving rise to gravel. Under ordinary cir- 

 cumstances, streams do not break up limestone and transport it in 

 masses, giving rise to limestone conglomerate at their debouchures. 

 Had there been limestone cliffs against which the waves of the 

 Triassic waters beat, or had there been scarps, at the bases of 

 which talus from limestone accumulated, the occurrence of lime- 

 stone conglomerate would not be strange, for in such situations 

 conglomerate and breccia containing a large proportion of limestone 

 may be formed. But at most points where the limestone conglomerate 

 occurs, there is now nothing to indicate that the areas of Triassic sedi- 

 mentation were bordered by limestone. If they were, the surface 

 exposures of the original formation have been destroyed, while its 

 derivative formation remains. Either erosion (Figs. 308 and 309) 

 or faulting (Figs. 310 and 311) might accomplish this result. If there 



Fig. 308.— Diagram illustrating the manner in which limestone conglomerate (below a) 

 might be formed along shore. //// = limestone. (Compare Fig. 309.) 



was faulting while the deposition of the series was in progress, fault 

 scarps, involving limestone, may have appeared about the borders 

 of the area of deposition. In this case, waves and descending streams 

 might have provided the material for the limestone conglomerate. 

 With the limestone, there is more or less other material derived from 

 the local rock formations; but at some points there are occasional 

 bowlders which do not correspond with any known formation of the 

 region. That they had a distant origin cannot, however, be asserted. 

 They may have come from formations now concealed or destroyed. 

 The exceptional coarseness of the conglomerate, at least locally, 



