DAVIS. — ROCKY MOUNTAIN TERTIARIES. 367 



are of equal and often of greater development. Whenever a low plain, 

 valley, or basin is for a comparatively long period but little elevated 

 above the base level of erosion, and during this time mountains and hills 

 stand about the lowlands, there must be a great accumulation of drift, 

 and where the highlands are areas of progressive elevation and the low- 

 lands areas of progressive subsidence this accumulation may continue 

 indefinitely" (Geol. Uinta 1 Mountains, 170, 171). 



Dutton's Report on the High Plateaus of Utah may be quoted to the 

 same end : " There is another class of conglomerates which claims our 

 special attention. These are of alluvial origin, formed, not beneath the 

 surface of the sea nor of lakes, but on the land itself. They do not seem 

 to have received from investigators all the attention and study which 

 they merit. . . . Throughout great portions of the Rocky mountain 

 region they are accumulating to-day upon a grand scale and have accu- 

 mulated very extensively in the past." After describing the transporting 

 action of torrents in mountains, and their depositing action at the moun- 

 tain base, the same author says : " The formation thus built up is an 

 'alluvial cone.' . . . The slopes near the circumference usually lie 

 between 1° and 2° ; those near the apex between 2° and 3|°. The 

 lengths of the radii of the bases often exceed 3 miles, sometimes exceed 

 4 miles, and seldom fall below 2 miles. ... So nearly together are the 

 gateways along the mountain and plateau flanks, each having its own 

 alluvial cone, that the cones are confluent laterally; giving rise to a con- 

 tinuous marginal belt . . . consisting of alluvial slopes which are sensibly 

 nearly uniform. . . . Our surprise is often great at finding the cone 

 wonderfully well stratified." Examples are then given of heavy Tertiary 

 conglomerates which are ascribed to an alluvial origin, although they are 

 " about as well stratified as the average of those which are attributed to 

 sub-aqueous deposition" (Geol. of the High Plateaus, 1880, 219-223). 



The occurrence of calcareous materials other than pebbles in fluviatile 

 and subaerial deposits is seldom discussed. Marls and limestones, even 

 if impure, are taken as evidence of marine or lacustrine conditions. 

 Yet earthy limestones are explicitly recognized among the strata of 

 the fluviatile plain of northern India, as above noted, and calcareous 

 material may be deposited as a cement in the piedmont wash of an arid 

 region. Concerning the latter, Hill writes as follows: — " Throughout 

 the limestone regions of the hot climates of America a superficial crust 

 of white-lime material is found, called tepetate. Sometimes it is compar- 

 atively free from foreign material, or occurs as the matrix or cement 

 of conglomerates. This is a concentrate of the lime which has been 



