CLIMATE AND TERRESTRIAL DEPOSITS 183 



each case indicating subaerial origin, much of which however is not 

 published. The dominant red color of the whole of the Triassic 

 formation, considered in connection with its feldspathic sandstones 

 indicative of the kind of erosion, mud-cracked shales, disseminated 

 gypsum, and calcite, indicative of conditions of sedimentation, point 

 on the one hand to a subarid climate, while the carbonaceous and 

 leached shales of the Rhode Island coal measures indicate a climate 

 markedly pluvial and cool. It is to be noted that in the Rhode Island 

 basin arkose conglomerates of local origin grade into carbonaceous 

 shales.^ The conglomerates are extremely abundant and except 

 in the Wamsutta red beds possess a light-gray matrix, while the shales 

 are usually darker in color. Thus the conclusion previously stated 

 is emphasized, that in humid climates, even in regions of rapid denuda- 

 tion and deposit, the finer materials eroded will show greater decom- 

 position and leaching than material of similar fineness, even when 

 derived more slowly from the erosion of surfaces of moderate relief 

 in arid climates. The character of the fine fluviatile or wash detritus 

 in the region of its origin may, therefore, be taken as an index of 

 climate. The size or abundance of the coarser material on the 

 other hand forms a measure of the rapidity of erosion, and roughly 

 of the degree of topographic relief. Where the matrix or the form 

 of the cobbles indicates, in association with other evidence, the presence 

 of arid or cold climates, however, disintegration dominates over 

 decomposition, and conglomerates in the region of erosion must be 

 correspondingly coarser and more abundant to indicate the same 

 relief as that of a more rainy region. In rivers sufficiently large so 

 that the erosion and deposition occur in different climatic zones only 

 the finer debris will reach the delta. The chief effect of rugged topog- 

 raphy in that case is found in the quantity of sediment and, as will 

 be further discussed in Part III under the topic of the "Effects of 

 Fluviatile Transportation," the evidence as to the climate of the 

 soucre becomes more obscure the farther the alluvium is carried. 



Separation of Tectonic and Climatic Oscillations 



A full discussion of this topic involves the effects of tectonic and 



climatic movements upon both transportation and deposition as well 



I A. S. Packard, "View of the Carboniferous Fauna of the Narragansett Basin," 

 Proceedings of the American Academy, Vol. XXXV, 1900, p. 405. 



