Reviews — Clarence King — Survey of Fortieth Parallel. 469 



ment of minerals, its various components lying more or less evenly 

 distributed throughout the mass." With regard to the genesis of 

 granite, the author supposes, were the chief factor to be tangential — 

 or, as he terms it, orographical pressure, there must of necessity be 

 all the h'ansitions from a uniform homogeneous granite down to 

 those rocks in which radial or gravitation has produced the ordinary 

 bedded schists. 



The Palaeozoic rocks, which are everywhere unconformable to the 

 underlying Archaean, are strictly conformable from the lowest 

 Cambrian beds to the top of the Upper Coal-measure Limestone. 

 Slightly developed in the Rocky Mountain system, not over 1,000 

 feet in thickness, they thicken out westward, as in the Wahsatch, to 

 more than 30,000 feet, and about 40,000 feet at the extreme western. 

 Palaeozoic limit. In the whole Palaeozoic section there are 18,000 

 feet of siliceous sediment, 13,000 feet of limestone, and about 1,400 

 feet of slates and shales. 



" The general absence throughout the Coal-measure horizons of 

 beds of coal, and the conspicuous absence of shallow- water deposits 

 (with the exception of some conglomerates), indicate that the whole 

 great Palaeozoic series was from the first received on the bed of a 

 deep ocean." Within the Palaeozoic series of this region there are no 

 considerable passages of metamorphism. 



Directly overlying the Palaeozoic limestones are the well-known 

 Eocky Mountain red-beds, which have been generally assigned to the 

 Triassic age. The Trias beds are succeeded conformably by the 

 Jurassic and Cretaceous groups, the exposures of which within the 

 Fortieth Parallel are clearly shown in Map III. (p. 356). Owing to 

 the widespread but unequal mechanical disturbance at the close of 

 the Palaeozoic period, the physical features of the old land area were 

 considerably modified, so that the Trias-Jura series were formed in 

 two separated seas, an eastern and western, differing in depth and in 

 the nature of their sediments (p. 537). 



Between the Cretaceous and Jurassic there is absolute conformity. 

 The former represented a period of comparative calm, so far as 

 orographic disturbances go, although it was characterized by subsi- 

 dences, but so general and gradual as to leave no traces of their 

 mode of operation, except the succession of conglomerates and tiers 

 of coal-beds. 



The Cretaceous group in descending order consists of — 1. The 

 Laramie or the Lignite group of Hayden, 1,500 to 5,000 feet. 2. 

 Fox Hill group, 3,000 to 4,000 feet. 3. Colorado group, equal to 

 Fort Benton, Niobrara and Port Pierre groups of Meek and Hayden, 

 800 to 2,000 feet. 4. Dakota group, 300 feet. 



With regard to the position of the upper member of this series 

 (the Laramie), considerable difference of opinion now exists, so that, 

 " aside from the Taconic system, no single geological feature in all 

 America has ever given rise to a more extended controversy than the 

 true assignment of the age of this group." 



Mr. Clarence King discusses the position of the Laramie group, 

 the geological horizon of which has been referred by Dr. Hayden and 



