120 REVIEWS 



far from twelve miles and whose breadth varies from a half mile to 

 two miles or more. This somewhat remarkable backbone of rock 

 early attracted the attention of Percival. It is noteworthy for its 

 hummocky structure, but it nowhere rises more than one hundred 

 feet above the general level. Careful study shows that the skeleton- 

 work of silica forms an intricate network which goes out from parallel 

 vertical walls of considerable thickness. These trunk lines or feeders 

 are shown to have the direction of parallel series of vertical joints 

 which had their origin in post-Newark time and were unquestionably 

 conditioned by a compression of the southwestern New England 

 region as a whole. The width of the silica walls forming the feeders 

 and the peculiarities of the silica network lead to the belief that the 

 same process of solution and removal of the dolomite which is now 

 widening joint planes in the area, operated subsequent to the forma- 

 tion of the joint planes and previous to the infiltration of the silica. 

 If it be true that surface conditions operated to widen joint fissures, 

 we must assume a depression of the area until this surface zone came 

 within the belt of cementation, for here only could the infiltration of 

 the silica have obtained, and thus a cycle of depression and elevation 

 of the area within post-Newark times must be supposed. 



TJie Freshzvater Tertiaries of Greeji River, Wyojiiivg. By W. M. 

 Davis. 

 A BRIEF visit to the Tertiary formation of Green River, Wyo- 

 ming, in the summer of 1902, sufficed to discover many variations of 

 texture in the strata that have usually been regarded as lacustrine. 

 Fine bedded cardboard shales frequently alternate with sandy layers 

 in which cross-bedding and ripple-marks are not uncommon ; some of 

 the strata contain small clayey pebbles cemented by calcareous mate- 

 rial, and closely resembling certain specimens of "tepetate" brought 

 from Mexico by R. T. Hill. It is believed that so great a variation of 

 texture is inconsistent with the generally accepted theory that the 

 Green River formation was deposited in a large and deep lake. The 

 deposits are better accounted for by deposition in a variable shallow 

 lake, possibly alternating from time to time with subaerial or fluviatile 

 conditions. 



The Basin Ranges of Utah a?id Nevada. By W. M. Davis. 



Several mountain ranges in the Great Basin of Utah and Nevada, 

 examined in the summer of 1902, are believed to be faulted blocks. 



