Reviews — Dr. Hayden^s Geological Reports. 33 



posed in succession, their dip diminishing as they recede from the 

 mountains, thus showing, in the words of Dr. Hayden, " that the 

 whole country west of the Mississippi to the Pacific, may be regarded 

 as a vast plateau, and that it was gradually elevated until the crust 

 of the more central portions was strained to its utmost tension, and 

 that it then burst, and along here evolved the lofty ranges which, 

 taken collectively, now pass under the name of the Eocky Moun- 

 tains." 



The lowest recognized stratum in this series is the representative 

 of the true Potsdam Sandstone, and this is the only record of Silu- 

 rian times visible in these regions ; neither is the Devonian present 

 in any form ; and the Potsdam Sandstone is directly succeeded by a 

 heavy formation of Carboniferous age, consisting, for the most part, 

 of yellowish limestones and sandstones, with fossils which, with us, 

 would be characteristic of the Lower Carboniferous, but which, in the 

 States, indicate the Upper beds of this age ; neither on their moun- 

 tain exposure, nor at their Eastern outcrop in Kansas, do these beds 

 give any promise of workable seams of coal. No distinguishable 

 Permian is to be seen in this Western series, though well known in 

 the East ; but a conspicuous unfossiliferous series of red arenaceous 

 deposits overlie the Carboniferous strata ; they are occasionally 

 saliferous and gypsiferous, and Dr. Hayden, with some hesitation, 

 refers them to the Triassic period. The upper beds of this forma- 

 tion pass insensibly into those above, which contain unmistakeable 

 evidence of their Jurassic age. These are especially interesting, as 

 giving us, in Nebraska, by far the most important and best authenti- 

 cated series of this formation, to be found in the United States ; 

 towards the South, however, they seem to thin out very considerably, 

 or even to disappear altogether. Above these again comes a vast 

 thickness (3,000 to 4,000 feet) of Cretaceous beds, to the division 

 and determination of which Dr. Hayden has devoted much time and 

 trouble. These Cretaceous rocks, being farther removed from the 

 nucleus of the mountain range, dip at a lower angle than the older 

 beds ; and still less in amount is the very thick series of Tertiaries, 

 which cover the whole country, from the base of the mountain land 

 to the re-appearance of the Cretaceous beds to the East. Although 

 he divides these deposits into Lower, Middle, and Upper Tertiary, 

 Dr. Hayden denies that they can be considered as exact equivalents 

 of our Eocene, Miocene, and Pliocene. 



Dr. Newberry, who supplements Dr. Hayden's Memoir with a 

 very interesting paper on the Cretaceous and Tertiary plants col- 

 lected in these districts, goes further, and pronounces the Lower 

 Tertiary to be of Miocene age. It certainly, in our opinion, bears 

 very little resemblance to what we are accustomed to as character- 

 istic of Eocene deposits. This will at once be evident, when we 

 quote the author (Dr. Hayden) respecting this formation, to which 

 he gives the name of Fort Union or Lignite Group : " It was 

 evidently deposited in large bodies of water, which were at first 

 brackish, and then gradually became fresh. The great number of 

 fossil leaves, and numerous beds of Lignite contained in it, clearly 



VOL. VIII. NO. LXXIX.. 3 



