DESCRIPTION OF THE ROCKS <Od I 



It was with this purpose that the writer presented to the Geological 

 Society, four years ago (December, 1911), the outline 2 of a paper entitled 

 "The mesozoic stratigraphy of Alaska." The work begun at that time 

 has developed into a rather extensive and elaborate treatise on the Meso- 

 zoic rocks of Alaska, which, although primarily a summary of exi sting- 

 knowledge, is to a large degree based on special field investigations, the 

 results of which have not hitherto been published. The studies men- 

 tioned above are now well toward completion, and the paper here pre- 

 sented includes some of the more important conclusions of general interest 

 derived from the preparation of the Triassic chapter of that work. 



Acknowledgments should be made to the many geologists, cited below, 

 who made the field observations that are the basis of the descriptions here 

 given, and also to Dr. T. W. Stanton, whose determinations of the fossils 

 are the substantial basis of the conclusions here presented. It should be 

 remembered that these field observations have been gathered, for the most 

 part, in the course of pioneer reconnaissance investigations and neces- 

 sarily are scanty and generalized. It should be remembered also that the 

 fossils have not yet been exhaustively studied. The determinations of 

 genera and species can be accepted as definite, except where a doubt is 

 expressed; but no attempt has yet been made to list all the species, many 

 of which are undescribed, or to determine the precise relations of the 

 faunas to those of .other regions. It is hardly necessary to add that the 

 writer has based his interregional correlations largely on the published 

 results of Prof. James Perrin Smith's elaborate studies and correlations 

 of the Triassic rocks of California, Nevada, and Oregon. Professor Smith 

 should not, however, be held responsible for the correlations of the Alaska 

 and British Columbia rocks except where he is directly cited. 



Description of the Triassic Rocks of Alaska 3 



occurrence and general character 



Triassic rocks are widely distributed in Alaska, being now known at 

 many localities (see map, plate 25) in nearly all parts of the three major 

 mountain regions and being absolutely restricted thereto. The most strik- 

 ing fact regarding the distribution of Triassic rocks in Alaska is this re- 

 markable agreement between the areas of present Triassic outcrops and 

 the areas of the major mountain regions. In this respect conditions in 

 Alaska are in accord with those in many other parts of the world. The 

 marine Triassic is, with good reason, called the Alpine Trias, for in 



2 Bull. Geol. Soc. Am., vol. 23, 1912, pp. 724-725. 



3 In the local descriptive matter here presented, footnote reference will be given for 

 only the latest or most comprehensive description of each formation. 



