624 abstracts: zoology 



In most of the gold-silver deposits quartz has replaced calcite gangue 

 to some extent, giving a peculiar platy structure to the quartz. With 

 the exception of the veins near Aurora the veins pi'oper carry almost no 

 sulphides although pyrite is found in the altered wall rocks. The gold 

 is all free but usually very finely distributed. At Aurora, besides free 

 gold, the ores carry tetrahedrite, some pyrite and chalcopyrite, and 

 selenium. The nature of the selenium compound is not yet known. 



So far as known all the silver-lead deposits are closely associated 

 with the intrusive quartz monzonite and related rocks and are therefore 

 of late Mesozoic or early Tertiary age. All these veins exhibit marked 

 similarity in the sulphide minerals, though the proportions of one to 

 another differ widely even in the same vein. Antimonial compounds, 

 generally freibergite, are present in practically every vein. Galena, 

 dark sphalerite, pyrite, arsenopyrite, and chalcopyrite are usually 

 fairly abundant. 



The copper deposits are associated with quartz monzonite intrusives 

 probably of early Tertiary age. Most of them are of the contact 

 metamorphic type or are replacement deposits in various kinds of 

 sediments near masses of intrusive rock. 



Most of the antimony deposits occur in crushed, contorted siliceous 

 shales. The ores consist of white quartz and stibnite, with, in some 

 places, minor quantities of tetrahedrite and galena, showing that they 

 are probably related to the silver-lead mineralization. E. S. B. 



ZOOLOGY. — A Study of asymmetry, as developed in the genera and 

 families of recent crinuids. Austin H. Clark, The American 

 Naturalist, 49: 521-546. 1915, 

 Among the recent crinoids any wide departure from the normal 

 close approximation to true pentamerous symmetry indicates unfavor- 

 able conditions of one or other of two main types, which are not mutu- 

 ally exclusive. These two types are: (1) Internal unfavorable condi- 

 tions, induced by incipient phylogenetical degeneration through type- 

 senescence, as in the PlicatocrinidiB which in the recent seas represent 

 the almost exclusively palaeozoic Inadunata; and (2) External unfavor- 

 able conditions, taking the form of (a) Phylogenetically excessive cold 

 which, to cite one example, appears to be the determining factor in 

 the asymmetry of the genus Promachocrinus, or (6) Phylogenetically 

 excessive warmth, which appears to be the determining factor in the 

 asymmetry of the Comasteridse. A. H. C. 



