CLIMATE AND TERRESTRIAL DEPOSITS 259 



Turning to the past for illustrations of these conclusions, we may 

 point out that the coarse, coal-measure conglomerates of the Narra- 

 gansett Basin and the less coarse, but still conspicuous, Triassic con- 

 glomerates of the Connecticut Valley, both give evidence of rather 

 local derivation and of continental deposition, evidence which cannot, 

 however, as previously stated, be here discussed in detail. The local 

 origin and coarse texture indicate deposition upon slopes of at least 

 from five to ten feet per mile and possibly much greater, sufficient, 

 under the usual climatic conditions, for good drainage. The Triassic 

 conglomerates of the Connecticut Valley show a large amount of 

 fragmentary fresh feldspar, iron completely oxidized, and no trace of 

 carbon, either in the matrix or associated red shales, the fish fossils 

 being found in the rare black shale bands. The conglomerates of 

 the Narragansett Basin, on the other hand, with the exception of the 

 Wamsutta beds, show a bleached matrix containing more or less car- 

 bon and are associated with a great volume of highly carbonaceous 

 shales. 



From these facts alone, therefore, it would be judged that the Car- 

 boniferous conglomerates, granting their subaerial origin, were accu- 

 mulated during a period of cool and more or less continuously rainy 

 climate. 



The Triassic conglomerates, on the other hand, are associated 

 with many features of climatic significance which also canaot be 

 taken up here in detail, but which independently indicate a semiarid 

 climate with hot summers and possibly cold winters. The character- 

 istics, therefore, of these conglomerates, originating from the same 

 geologic province, but in climatically dissimilar geologic times, are 

 such as to emphasize the importance of the present conclusions regard- 

 ing climatic influences upon the deposits of piedmont slopes. Further 

 discussion of this subject must be left for the section on climatic 

 influences. 



LOWER FLOOD PLAINS — AQUEOUS DELTAS 



The slope of graded streams progressively diminishes from source 

 to mouth, the larger and longer the stream the flatter the grade tending 

 to become. The deltas of the larger rivers commonly possess a slope 

 of less than a foot per mile, and on the seaward margin pass into 

 practically level salt-water marshes, underlaid by heavy deposits of 



