Geology. 85 



To make the foregoing criticisms specific by citing an illustra- 

 tive point : it is inferred by Joly that uranium is concentrated in 

 the outer hundred miles of the crust because if it extended indefi- 

 nitely downward in the same amount, the energy liberated would 

 be more than sufficient to maintain the temperature gradient. 

 This inference, however, has no supporting evidence and leads in 

 turn to some assumption as to the manner in which uranium 

 could be so concentrated and yet remain in its extremely diffused 

 state. On this inference of the subsurface concentration is never- 

 theless based an explanation of the making of mountains and of 

 continental and oceanic movements. As other allowable infer- 

 ences which would meet the same condition of a subsurface 

 excess in radio-activity, it may be suggested that in the deep body 

 of the earth the pressures and temperatures, greater than any 

 attainable in the laboratory, may partially or completely inhibit 

 the radio-active degradation of uranium, or offsetting heat- 

 absorbing reactions in other materials may take place, or igneous 

 activity may serve as a safety valve to reduce the excess of 

 internal energy transmuted from subatomic to atomic form. 

 These are all speculations which have not been disproved. None 

 of them may be true, but they indicate the danger of arriving at 

 conclusions supported on a complicated superstructure of reason- 

 ing when the stability of the foundation premises is open to 

 serious question. In considering the problems connected with 

 internal terrestrial activities the field of the unknown is so large 

 that the method of multiple working hypotheses should be more 

 largely employed than is done in this volume. Nevertheless 

 much is brought out which is stimulating and suggestive, j. b. 



2. The Geology and Ore Deposits of Goldfield, Nevada; 

 by F. L. Ransome. TJ. S. G. S., Prof. Paper No. 66, pp. 253, 

 35 plates, 34 text fig. Washington, 1909. — The Goldfield district 

 consists essentially of a low, domical uplift of Tertiary lavas and 

 lake sediments resting upon a foundation of ancient granite and 

 metamorphic rocks. The erosion of this flat dome has exposed 

 the pre-Tertiary rocks at a number of places in the central part 

 of the district, and these outcrops are surrounded by wide con- 

 centric zones of successively younger formations. Some of the 

 later lavas were erupted after the dome had been elevated and 

 truncated. The pre-Tertiary rocks consist to-day of quartz rocks 

 intruded by masses of a granitic rock like that to which the name 

 alaskite has been given. The Tertiary lavas include dolerite, 

 rhyolite, basalt, andesite and latite. Most of these are found in 

 different flows of different periods and lying between them are 

 various fragmental rocks. 



The sulphide ores of the Goldfield district are of complex miner- 

 alogical character, native gold and pyrite being accompanied by 

 minerals containing copper, silver, antimony, arsenic, bismuth, 

 tellurium, and other elements. In some ores the gold occurs free 

 in fine particles, which, as a rule, are aggregated together to form 

 yellow bands or blotches. The associated minerals are pyrite, 



