Geology and Natural History. 159 



acter of this region is the modification of the peneplain by warp- 

 ing so as to form anticlinal ridges and synclinal valleys. In the 

 Wenatchee-Chelan district glaciation furnishes an additional 

 datum plane and Mr. Willis has worked out the physiography in 

 great detail. He recognizes five physiographic stages from the 

 Pliocene to the Recent, inclusive. As a study of physiographic 

 method and of criteria for recognizing peneplains this paper is a 

 valuable addition to geologic literature. 



2. Alaska, Glaciers and Glaciation; by G. K. Gilbert, 

 being Vol. Ill of the Harriman Alaska Expedition reports, pub- 

 lished with cooperation of the Washington Academy of Sciences. 

 New York, 1904. (Doubleday, Page & Co.) 231 pp., 18 maps 

 and plates, 106 figs. — This most instructive and suggestive report 

 may be briefly reviewed under four headings : preglacial land 

 forms, erosion by Pleistocene glaciers, existing glaciers, and gla- 

 cial erosion in general. A noteworthy feature of the preglacial 

 topography was the occurrence of mountain ranges formed by 

 the broad uplift and dissection of extensive peneplains, which, it 

 may be here noted, are but so many additional instances of the 

 difficulty into which Suess's hypothesis of the origin of horsts 

 must lead the geologist. These peneplains and the neighboring 

 ocean were once at (almost) the same level : according to Suess' 

 hypothesis, the peneplains have become horsts, not by local eleva- 

 tion, but by the depression of the surrounding surfaces ; and in 

 this case, as in many others where horsts have ancient peneplains 

 for their uplands, it is evident that such an explanation involves 

 the depression of all the oceans of the world, and the continents 

 along with them, the horsts alone standing still. This is of course 

 conceivable, but it is an extravagant conception. Certain parts 

 of the coast show lowlands of denudation adjacent to the moun- 

 tains, thus recalling the coast plain of Norway as described by 

 Reusch. Gilbert explains the Alaskan coast plain by general 

 erosion when the land had gained something like its present 

 altitude, and does not explicitly call upon marine erosion, as 

 Reusch did for the Norwegian example. Erosion of valleys to a 

 greater depth during a time of greater elevation is also inferred, 

 but hardly proved, unless it is held that glacial erosion cannot 

 have scoured out the channels now occupied by the sea while the 

 land held its present position. 



Gannett's thesis that a glaciated valley is comparable with a 

 river channel is supported by a great variety of facts. Cirques 

 and hanging valleys characterize the coastal mountains : repeated 

 examples are figured and described. In this connection reference 

 may be well made to the Chief Mountain (Montana) map sheet, 

 lately issued by the U. S. Geological Survey, an elegant example 

 of fine topographic work by Messrs. Matthes and Sargent, in 

 which cirques and hanging valleys are remarkably well portrayed. 

 Indeed so numerous are the examples of these forms in once- 

 glaciated mountains in many parts of the world that the occa- 

 sional occurrence of imitative forms in non-glaciated districts can 



