CARBONIFEROUS 303 



Chicliagof island.^-" The fauna of these limestones at Freshwater bay 

 show them to be the equivalent of the Calico Bluff formation of the Yukon 

 section. The}' appear to rest on an igneous series which is probably of 

 Upper Devonian age. 



The Upper Carboniferous limestone, which is about 600 feet in thick- 

 ness, is exposed in the Pybus Bay section on Admiralty island. It is trun- 

 cated above by a Mesozoic limestone, which is iinconformable to it. A 

 series of highly siliceous argillites of undetermined thickness underlies 

 the Upper Carboniferous limestone at Pybus bay, of which about 800 feet 

 are exposed. These include beds of various colored (chiefly black and red) 

 siliceous argillites. Both the siliceous argillites and the Upper Carbon- 

 iferous limestone occur on the coasts of Ivupreanof and Ki;iu islands, and 

 are probably widely distributed in southeastern Alaska. The Upper 

 Carboniferous limestone of southeastern Alaska contains a rich fauna 

 which is so closely allied to that of the Upper Carboniferous limestone 

 of the Yukon as to leave no question as to their equivalence. The argil- 

 lite series occurring between the Upper and Lower Carboniferous lime- 

 stone in southeastern Alaska should jDrobably be correlated with the 

 Nation Eiver formation of the Yukon. No fossils are known from the 

 rocks of either series, but similar relationships which they seem to sustain 

 to the limestone formations of the two regions suggest their provisional 

 correlation at least. 



It is evident from the foregoing that, while the threefold division of 

 the Yukon Carboniferous can not be carried through the Carboniferous 

 section of all the adjacent provinces, yet certain of the stratigraphic units 

 are known to have a wide distribution. 



The beginning of the Carboniferous time in the inland region was 

 marked by no period of erosion or dynamic disturbance, sedimentation 

 being unbroken from the Devonian. There was, however, a gradual 

 change from land-derived material to that of a purely calcareous charac- 

 ter, which was accompanied by the appearance of a new fauna. What 

 the limits of the sea in which these rocks were deposited were can not 

 now be stated. It probably covered much of the present Yukon basin, 

 and certainly covered southeastern Alaska. In northern and northwest- 

 ern Alaska the oldest Carboniferous is also represented by a limestone 

 series, but the included faunas are somewhat different from those of the 

 Yukon. Calcareous sedimentation continued on the Yukon until prob- 

 ably more than 1,000 feet of strata were accumulated, and then there 

 appears to have been elevation above the water and erosion. Tlie suc- 



i»> E. M. Kindle : Notes on the Paleozoic faunas of southeastern Alaska. Journal of 

 Geology, vol. 15, 1907, p. 331. 



JiXIX — But^L. Gkol. Soc. Am.., Vol. 10, 1907 



