258 A. H. BROOKS RECONNAISSANCES IN SOUTHEASTERN ALASKA 



occupy large areas in Prince of Wales, Baranof, Chichagof, and Admi- 

 ralty islands. 



These four formations, (1) the white limestone and phyllite, (2) the 

 blue limestones, (3) the black phyllite and arenaceous schists, and (4) 

 the Coast Range granite, form the country rock of the larger part of 

 southeastern Alaska. There are also younger sediments, volcanic rocks, 

 and various types of intrusives in. this field. 



The oldest beds of the region in which fossils have been found are the 

 limestone outcropping on the shores of Glacier bay.* Professor Cush- 

 ing found a few fossils in this limestone, which were determined as 

 Paleozoic by Professor H. S. Williams. Later, on the evidence presented 

 by these fossils and on that of coral collected from the Dirt glacier by 

 Professor J. J. Stevenson, these limestones were assigned to the Carbonif- 

 erous.f It will be shown below that the latter fossil is from an entirely 

 different horizon. Through, the kindness of Professor Williams the 

 Drake Island material was submitted to Mr Charles Schuchert, to whom 

 the writer is indebted for the following report on three fossils: 



' ' I have examined the Drake Island material and find a large Leperditia of the 

 L. baltica group. 



" Megalomus sp. undet.; sections of a very large species very similar to M. cana- 

 densis. 



" Hormotoma sections, like several found in the Guelph of Ontario. 



" The species on which one can depend for age determination is the Leperditia. 

 These large species of Leperditia cease with the basal beds of the American Devo- 

 nian (Lower Pentamerns = Coeymans), but 'their greatest abundance is in the 

 Wenlock and Dudley horizons of Europe. The Glacier Bay species is unmistak- 

 ably related to the L. baltica of the Upper Silurian. Further, it is not related to 

 the large Lower Silurian forms of the L. flabulites group, and this is again shown 

 by the presence of very large bivalve shells, which I take to be of the gen as 

 Megalomus, a fossil so characteristic of the late Upper Silurian. Even if the large 

 shells are not Megalomus these Leperditias alone prove that the limestone can not 

 be younger than the late Upper Silurian. It is true that the genus Leperditia is 

 stated to occur as late as Lower Carboniferous time (L. carbonaria Hall, L. nicklesi 

 Ulrich), but all the Devonian and Carboniferous species are minute forms, and if 

 they do not belong to other genera, which seems probable, they certainly can not 

 be included in the L. baltica group of Leperditia. 



"The coral identified as Lonsdale ia comes from another locality (Dirt glacier) 

 more than fifteen miles away, and can not be included in the Drake Island fauna. 

 To this locality one should for the present restrict the type section for the ' Glacier 

 Bay limestone,' for the reasons above given, and for the further one that the coral 

 was not found in situ." 



Reid and Cushing found argillites underlying the limestones conform- 

 ably and both forming a closely folded series. This series has been 



*Nat. Geog. Mag., vol. iv, p. 59 ; 16th Ann. Rept., part i, p. 433. 

 f Sixteenth Ann. Rept., part i, p. 434. 



