240 J. Barrett — Upper Devonian Delta of the 



washing of upland waste into streams, while at the same 

 time the capacity of the streams to carry waste is increased. 

 The rivers consequently load up by eating into the higher parts 

 of the piedmont slope, the more readily because of the uncon- 

 solidated nature of the deposits ; the river grade outside of the 

 mountains is flattened and there is a transfer of coarser material 

 to the delta or the sea. A conglomerate of climatic origin is the 

 result, interbedded with normally finer grained deposits. A 

 reverse climatic movement will build up again the higher part6 

 of the slope, steepening the grade in this part and giving a 

 minimum supply of waste to the delta until equilibrium be- 

 tween grade and climate is established. In general it may 

 be said that climatic fluctuations of any nature will produce 

 alternate terracing and filling in the upper parts of the pied- 

 mont plain ; asynchronous alternation of thick and coarse with 

 thin and tine deposits upon the delta topset beds, both on the 

 land and extending to the shallow sea. 



The repeated cutting and filling during the Pleistocene 

 of the valleys crossing the High Plains seems, as W. D. 

 Johnson has pointed out, to have been most largely of a cli- 

 matic cause, and the same conclusion has been reached for the 

 terracing in other regions by Davis and Huntington. The 

 subject has been discussed more fully by the writer elsewhere, 

 with some application to the Appalachian deposits of the Upper 

 Paleozoic* 



The question arises, how such a climatic record may be 

 discriminated from a somewhat similar record made as the 

 result of crustal movements. The clearest distinction is in the 

 relations of carbon and iron oxide as seen in the shale mem- 

 bers of the delta deposits ; an increase in the quantity of carbon 

 marking a movement toward wetter or cooler climates, an 

 increase in oxidation marking the movement in the contrary 

 direction. 



The results to the delta would be quite different if there 

 were no storage of coarse siliceous waste in a piedmont slope 

 between the mountains and the all a vial flats beyond. Then 

 the movement toward a greater growth of vegetation would 

 normally decrease the supply of coarse waste to the rivers and 

 increase the deposit of carbon to the delta. Certain exceptions 

 may, however, be imagined : — a climatic movement which 

 would bring on glacial conditions in the mountains would carry 

 coarser waste farther from them without deriving such from a 

 piedmont slope and at the same time favor the storage of car- 

 bon in the parts of the delta which did not receive this waste. 

 Alluvial gravels of ultimate glacial origin derived from a crys- 



* Barrell : Relations between Climate and Terrestrial Deposits, Jour. Geol., 

 xvi, pp. 162, 163, 363-384, 1908. 



