abstracts: geology 95 



thin from having been squeezed it is higher in ash. The coal in the 

 same mine therefore may be high in graphite and ash where it is thin, 

 and freer of both ash and graphite in the wider pockets. 



The field as a whole appears to have been subjected to large regional 

 differences in pressure and there are corresponding regional differences 

 in the coal. 



Rhode Island coal is a high-ash, high-moisture, graphitic anthracite 

 of high specific gravity. R. W. S. 



GEOLOGY. — The Broad Pass region, Alaska. Fred H. Moffit, 

 with sections on Quarternary deposits, igneous rocks, and glaciation, 

 by Joseph E. Pogue. U. S. Geological Survey Bulletin No. 608. 

 Pp. 80, with maps, section and views. 1915. 



The region described lies south of the axis of the Alaska Range and 

 includes part of the headwaters of Susitna, Chulitna, and Nenana 

 rivers. Rocks ranging in age from Devonian to Tertiarj 7 are exposed 

 and in addition unconsolidated deposits of glacial, glacio-fluvial, and 

 fluvial origin are present. 



The Devonian rocks include limestone, slate, and conglomerate, all 

 of which are folded and otherwise altered. In places the slate and con- 

 glomerate have become schistose. Rocks tentatively referred to the 

 Triassic are basaltic lavas apparently overlain by dark-blue and black 

 slates with interstratified arkose and graywacke. Other dark-blue 

 and black slate s interbedded with graywacke and conglomerate are 

 tentatively referred to the Jurassic and a complex of sedimentary rocks, 

 chiefly slate and limestone, are considered to be probably Mesozoic. 

 The principal Tertiary rocks are the Cantwell formation (Eocene), 

 a massive conglomerate, locally containing fossiliferous shale beds. 

 It is folded and in its eastern extension takes on a schistose structure. 



All the consolidated sediments are cut by intrusives, most of which 

 are granitic or porphyritic and of felsic (acid) character. The youngest 

 intrusives are of Tertiary age. 



The Broad Pass region has been profoundly glaciated, as is plainly 

 shown by its topography. 



Mining has not been established here. The region, however, is 

 favorable for prospecting. F. H. M. 



