March 24, 1911 | 



SCIENCE 



463 



that conclusion. Quartz, actinolite, calcite and 

 iron ores appear as alteration proceeds, and tlieir 

 relations have been noted. The green mineral 

 first appears at a depth of 1,508 feet, where it 

 is only partially developed and hardly to be dis- 

 tinguished from the isotropic glass. It occurs in 

 various forms and first attracted attention as it 

 took the rounded form of the original glass pel- 

 lets, wholly free from other secondary minerals. 

 The detailed relations were examined. Geodic 

 structure often appeared. 



Inasmuch as these several secondary minerals 

 often lie in a matrix of greeualite, it has been 

 assumed that they have been developed from the 

 greenalite by chemical separation. But an iden- 

 tical fact is seen in the relations of secondary 

 quartz. Magnetite, actinolite, and even greenalite 

 and calcite are similarly surrounded by quartz. 

 From analogy, one might assume that these min- 

 erals were generated from quartz. On such an 

 assumption any one of the minerals could be 

 proven to be derived from any of the others. 



These considerations put a veto on the idea 

 that the iron ore is derived from the greenalite. 

 It is a secondary product coordinate and connate 

 with the quartz and with the iron ore. 



An Example of Limonite Deposition: Olivek 



Bowles. 



A small occurrence of limonite at Sturgeon 

 Lake, in the Thunder Bay District of Ontario, is 

 described. Surface waters have dissolved pyrite 

 from a pyritie quartz vein which is exposed on a 

 hillside, and the dissolved iron is deposited in the 

 form of a limonitic cement amongst the pebbles 

 of the talus slope. 



The points to which attention is specially di- 

 rected are:' (1) evidence of total solution of 

 pyrite by rain water assisted only ' by dissolved 

 gases; (2) the large extent of the deposit when 

 compared to its limited source of supply; (3) the 

 presence of ferrous sulphate as an intermediate 

 stage in the process of alteration. The unstaDle 

 nature of ferrous sulphate when considered in 

 connection with the close proximity of the pyrite 

 and limonite would Isad one to expect that lim- 

 onite deposits of pyritie origin, in regions free 

 from carbonate reaction, would be found close to 

 the source of supply. 

 The Geology of the Cuyuna Iron Ore District of 



Minnesota: Carl Zapffe. 



Cuyuna District is located in central Minnesota 

 and is the youngest iron-ore district in the Lake 



Superior region. No rock outcrops point directly 

 to its location, but its existence was conjectured 

 from the geological structure of the Lake Superior 

 region as a whole and that of the diiferent iron- 

 ore districts embraced therein. Numerous well- 

 defined belts of magnetic attraction enable sys- 

 tematic and productive explorations with diamond 

 drills, and the geology of the district has been 

 determined solely from carefully collected data of 

 about 1,900 drill holes. The geology of the dis- 

 trict is interpreted to be that of a closely folded 

 heterogeneous slate formation of Upper Huronian 

 age and containing in its lower horizon inter- 

 bedded sedimentary lenses of iron-bearing forma- 

 tion which, upon being exposed by folding and 

 erosion, have frequently altered through descend- 

 ing meteoric waters into low-grade iron ores at 

 the erosion surface. Basic post-Huronian igneous 

 rocks seem to be exclusive within the ore-bearing 

 area and predominate over the acid phase in the 

 outlying areas. 



The Belation of Texture to the Composition of 

 ~Coal: Frank F. Grout. 



Proximate and ultimate analyses are reported 

 of seven samples from a coal mine at Marshall, 

 Colorado. The samples represent different tex- 

 tures from a single seam, and in the report they 

 are distinguished by the following names: (1) 

 average, (2) glance coal, (3) splint coal, (4) 

 mineral charcoal or "mother coal," (5) cannel- 

 like coal, (6) resin? (7) slate, (8) bone coal. 



It is seen that the average of the seam is sub- 

 bituminous, but that by any of the standard 

 methods of chemical classification the small sam- 

 ples vary from lignite to semi-bituminous coal. 

 The analyses have considerable importance in dis- 

 cussions of the origin of coal, and further, may 

 explain some of the variation in samples from a 

 single seam. It is well known that such con- 

 stituents as the resin and charcoal occur quite 

 erratically in various parts of the mines. 



The Geology of Harding County, South Dalcota: 



Ellwood C. Perisho. 



This area is located in the northwest corner "of 

 South Dakota. Topographically the chief feature 

 is a plain about 3,000 feet in elevation with sev- 

 eral buttes and a few valleys. The buttes are 

 about 500 feet high; good examples are Cave 

 HUls, Short Pine Hills and Slim Buttes; while 

 the chief vaUeys are the Little Missouri, Grand 

 and Moreau. The geological formations are the 

 Fort Pierre, Cretaceous to Loup Fork and Mio- 



