Apbil 1, 1910] 



SCIENCE 



517 



The lithium and gem minerals occur in the bottom 

 of the upper part and consequently near the 

 center of the entire body. A number of distinct 

 structural varieties of pegmatite may be recog- 

 nized, all formed by vedn processes. 



Tlie Cobalt Mining District of Ontario: Mr. S. 



F. Emmons. 



The features of the Cobalt silver deposits that 

 most strikingly differentiate them from those of 

 most mining districts are: 



ilineralogically, the predominance of the metals 

 cobalt, nickel, silver and bismuth, with an almost 

 total absence of lead and zinc, and their prevalent 

 combination with arsenic and antimony rather 

 than with sulphur. 



Structurally, the extreme narrowness of all the 

 rock fractures, and the general absence of evidence 

 of any considerable displacement such as is af- 

 forded by slickensides or clay selvages. Neverthe- 

 less, very decided proof exists that the veins are 

 true fault fractures, not contraction cracks, in 

 that they contain dragged-in fragments of wall 

 rock, that they pass uninterruptedly from one 

 rock formation to another, even though separated 

 by a great unconformity, and that in the coarse 

 so-called conglomerate, in which they were first 

 discovered, they cut through matrix and included 

 fragments indifferently. They seem to be frac- 

 tures that have been produced under so great a 

 load of overlying rocks that movement had been 

 greatly restricted. 



Genetically, the predominance of silver in the 

 metallic state over its combinations with sulphur, 

 arsenic and antimony; and the remarkably abrupt 

 falling off in the tenor of this metal from the 

 bonanza zone, where it is measured by thousands 

 of ounces per ton, to the ordinary low-grade 

 cobalt vein with less than ten ounces, a change 

 that takes place within very few feet. 



These facts seem best explained on the assump- 

 tion that the present veins are only the roots of 

 veins that were originally of great vertical extent 

 but have been mostly worn away; and that these 

 remaining vein roots have been gradually enriched 

 by successive leachings-back for unusually long 

 geological periods (for both primary and sec- 

 ondary vein fractures are of pre-Cambrian age). 



The secondary fractures within the veins that 

 carry the most of the silver are probably not the 

 channels through which the silver was originally 

 introduced, but simply those which, by the admis- 

 sion of solutions leached down from the surface, 

 have produced an extraordinary enrichment in 

 this metal. 



The conclusion seems warranted, therefore, that 

 the rich silver veins are not, as was originally 

 assumed, confined to any particular formation, 

 and that while the bonanza portion of individual 

 veins has a limited extent in depth, the abundance 

 of small fractures or calcite veins, that may at 

 any time pass into bonanza, renders the future 

 of the district very promising. 



The Mechanical Part of a Paleontologic Mono- 

 graph: Lancastee D. Bdeling. 

 The value of a monograph depends so largely 

 upon the accessibility of the miaterial which it 

 contains that current methods are believed to be 

 inadequate for the proper presentation of the 

 results of careful research. Some improvement in 

 the monographic treatment of paleontologic sub- 

 jects may be accomplished by the introduction of 

 the following features. They should be regarded 

 as merely an initial step in what is believed 

 should be a general attempt to raise the standard 

 of monographic methods. 



1. A list giving the present reference of every 

 generic or specific name occurring in the syn- 

 onymy, arranged alphabetically by specific as well 

 as generic and subgeneric terms. 



2. Detailed localities with locality numbers 

 (original where possible or arbitrary where taken 

 from the literature) and a list of the localities 

 giving them in detail (with reference to published 

 sections if possible) and citing the included 

 species. 



3. Sections typical of each general area or 

 province covered by the monograph, giving in one 

 column the species occurring in the section and 

 in a second the species occurring elsewhere 

 throughout the larger area in their approximate 

 stratigraphic position; tables, arranged by faunal 

 provinces, showing at a glance the species occur- 

 ring in the major subdivisions of each; and sum- 

 mary tables showing the general geographic and 

 stratigraphic distribution of the species, the gen- 

 era and the families, respectively. 



4. Descriptive notes indicating the source from 

 which all or any part of each reference in the 

 synonymy may have been copied, or the place in 

 which any part of it may be duplicated, etc., and 

 supplementary foot-notes under each genus giving 

 a chronologic list (with references) of the various 

 genera to which the species now placed in the 

 genus have been referred. 



5. Complete descriptions of plates naming the 

 type specimens, giving the locality and catalogue 

 numbers, and outlining a complete history of each 

 previously figured specimen. 



