276 Brief Notices. 



Mesozoic or Tertiary strata, as well as Pliocene and later deposits. 

 Gold has been obtained in profitable quantity from the Hurrah quartz 

 mine, the associated slaty rocks being possibly of Devonian age ; but 

 most of the gold is obtained from placer deposits, of which detailed 

 accounts are given. Among the metamorphic rocks there is great 

 complexity of structure, recumbent overturned folds and extensive 

 thrust-faulting being described. 



Bulletin 435, 1910, records " A. Reconnaissance of parts of- North- 

 Western New Mexico and Northern Arizona ", by Mr. N. H. Darton. 

 The country here described and shown on a geological map extends 

 along the borders of the railway from Albuquerque on the east to 

 Peach Springs and Kingman on the west. A variety of formations is 

 exposed — Pre-Cambrian, Cambrian, Devonian, Carboniferous, Triassic, 

 Cretaceous, Tertiary, and Quaternary. The region lies mostly in the 

 plateau province, and it includes the Grand Canyon in North Central 

 Arizona, where the ground rises to more than 8,500 feet and the deep 

 gorge is at its base 2,436 feet above sea-level. Some effective views 

 are given of the Canyon, of pre-Cainbriim granite with nearly vertical 

 jointing, of the Wingate Sandstone (Triassic), of Bad Lands, a typical 

 desert valley, and of a recent volcanic cone, etc. In the ' petrified 

 forest ' of Arizona, which is of Triassic age, the logs occur in 

 a conglomeratic sandstone, the ' Lithodendron formation', but as the 

 beds are eroded the silicified trunks accumulate at the surface at 

 various levels. The principal species, Araucarioxylon arizonicum, was 

 described by Mr. F. H. Knowlton. The higher portion of the Trias, 

 known as the ' Painted Desert formation ' on account of its banded 

 and brilliantly coloured sandstones, may possibly include beds of 

 Jurassic age. 



The principal mineral resources of the area are coal and copper ; but 

 asbestos, gold, gypsum, limestone, and building-stone are of importance. 



Bulletin 425 deals with the practical question of "The Explosibility 

 of Coal Dust ", by Mr. G. S. Pice and others. Bulletin 429 treats of 

 " Oil and Gas in Louisiana, with a brief summary of their occurrence 

 in adjacent States ", by Mr. G. D. Harris. The author deals with 

 the occurrence of oil and gas (1) in "Saline Domes", the nuclei of 

 which are generally found to be made up of rock-salt, while oil and 

 gas have been concentrated in enormous quantities, the surrounding 

 territory being barren, and (2) in " Stratum oil and gas fields", where 

 the materials are coextensive with certain widespread geological 

 strata, though occurring in commercial quantities only in areas where 

 the structure is favourable. 



A "Preliminary Keport upon the Oil and Gas developments in 

 Tennessee " has been prepared by Mr. M. J. Munn for the State 

 Geological Survey of Tennessee (Bulletin 2e, 1911). 



VI. — Brief Notices. 

 1 . Iowa. — In an account of ' ' The Pleistocene Deposits in Warren 

 County, Iowa " (TJniv. Chicago Press, 1911), Mr. J. L. Tilton discusses 

 the physical changes which the area has undergone in Quaternary 

 times. The pre-Glacial topography was wholly unlike that of the 

 present; it was almost entirely obliterated by the " sub-Aftonian 





