Revieivs — A. H. Brooks- — Mount McKinley, Alaska. 87 



Gault is overlapped by Upper Green sand in the West of England, it 

 should have been pointed out that the Gault in point of aji;e is still 

 represented in the basal sandy and loamy beds of the Upper Greensand. 



From the descriptions and diagrams tlie student will soon grasp the 

 relation of the rocks to the form of the ground and of outcrops to 

 contours ; and in a field-survej' he will learn to complete his 

 geological boundary-lines from the actual data observed along stream 

 courses and scarps of rock, across tracts where the guides are mainly 

 in the shape of the ground, and in the occasional outbreak of springs. 



While the work, as implied in its title, does not deal with the 

 variety of subjects of importance to the geological surveyor, such as 

 are discussed in W. H. Penning's Engineering Geology (1880), in his 

 Text Book of Field Geology (2nd ed., 1879), and in Sir A. Geikie's 

 Outlines of Field Geology (5th ed., 1900), it will be exceedingly 

 useful for study and reference on the interpretation, the uses, and 

 method of construction of geological maps and sections. 



III. — The Mount McKinlez Kegion, Alaska. By Alfred H. 

 Brooks ; with descriptions of the Igneous Rocks and of the 

 BoNNiFiELD AND Kanteshna DISTRICTS, by L. M. Peindle. 

 Professional Paper 70, U.S. Geological Survey, 1911. 



IN this quarto volume the authors have given a full account of what 

 is known of the geology, physical features, and mineral wealth of 

 the region, together with a history of previous explorations, and useful 

 notes on the equipment necessary for the traveller. The climate, 

 vegetation, and animal life are described, and it is pointed out that 

 there is available a large amount of arable land, while the region also 

 furnishes one of the best game-fields in Alaska. 



The oldest rocks, which are probably pre-Ordovician, comprise 

 schists, gneisses, quartzites, and subordinate limestones ; then follow 

 Ordovician (with graptolites), Silurian (?), Devonian (with corals, etc.), 

 and Carboniferous (?). Triassic strata occur in Central Alaska, but 

 not in the area now described. The Jurassic rocks contain andesitic 

 and other lavas in. the lower portions and some coal-seams (as yet 

 undeveloped) in the higher strata. Cretaceous rocks are represented 

 by limestone, black slates, and conglomerate. The Tertiary strata 

 consist chiefl.y of freshwater beds belonging to the Kenai formation 

 (Upper Eocene), and they contain important beds of bituminous and 

 lignitic coals. There are also andesitic, basaltic, and rhyolitic lavas 

 of post-Eocene and in part Pleistocene age, and extensive Pleistocene 

 and Recent glacial and alluvial deposits. 



The Igneous rocks are described by Mr. L. M. Prindle. The 

 intrusive rocks are chiefly granites, granodiorites, and diorites. They 

 occur in the Alaska range, where Mount McKinley rises to a height 

 of about 20,300 feet, and in some other mountain tracts, including 

 that of Talkeetna. There they appear to be mainly of late Jurassic 

 age, but in other parts of Alaska some intrusions may be of Upper 

 Carboniferous age, while others extend into Upper Cretaceous. There 

 are no active or extinct volcanoes in the region. 



Gold placer deposits are widely distributed in the Quaternary 



