102 REVIEWS 



Finally the author concludes that "dikes, sheets, laccoliths, 'byama- 

 liths,' and perhaps a few of the smaller stock-like plutonic bodies are 

 conceived to be due to crustal displacement permitting intrusion ; that 

 marginal assimilation in the preparation of subterranean magma cham- 

 bers is quite subordinate to magmatic overhead stoping ; and that 

 abyssal assimilation, in contrast to marginal {hypabyssal), is responsible 

 for the preparation or notable modifications of magmas whence come, 

 through differentiation, the igneous rocks of the globe." 



A Structural Section of a Basin Range. By George D. Louder- 

 bock, Reno, Nevada. 



The prevalent idea of the structure of the "Basin ranges" having 

 been called into question, a structural section of the Humboldt Lake 

 Range and adjoining country is presented as a contribution to the dis- 

 cussion. This range, where studied, is shown to be made up of strata 

 of the Triassic and Jurassicperiods, faulted, folded, in places overturned, 

 which were greatly eroded, in fact were practically in a peneplained 

 condition, before the outpouring of the Cenozoic volcanics. Over 

 their upturned and eroded edges lies a volcanic series made up of rhyo- 

 lites, rhyolite tuffs — some being current bedded, and with conglomer- 

 ate layers — capped by basalt. This series is faulted and tilted in a 

 simple manner, in great contrast to the older rocks. Reasons are 

 given for believing that these volcanics were laid down at an approxi- 

 mately horizontal attitude, and that the volcanics of the range and 

 those of the valleys on either side were continuous. On the east slope 

 of the range, the series passes from the summit to the base, with some 

 20° dip, and disappears under the detritus of the valley. On the west 

 slope they are not to be found, but they occur at the west base, butting 

 into the range at an approximately horizontal attitude, indicating a 

 fault on the west side and simple tilting of the range as a compara- 

 tively rigid block. 



A well-checked use of the volcanic rocks, which are so abundant in 

 the Great Basin region, to determine the character and extent of the 

 more recent earth movements is urged, and examples are given from 

 other ranges where it has proved of value. 



The structure of the range may also be arrived at by the application 

 of the physiographic criteria so concisely stated by Davis;' for (i) the 

 range has a unity, and a consistent front, and while lying between 

 broad flat valleys, it shows no approximation to broad intermontane 



