REVIEWS 719 



author's investigation. A study of the origin of peat follows, which 

 throws some light on the way in which coal was formed in Paleozoic 

 times. The author's study of the structure of coal embodies the results 

 of his examinations of a number of different Paleozoic coals. Particular 

 attention is given to microscopic studies, many of which were made with 

 a magnification of 1,000 diameters, approaching the limit of visibility. 



The text is accompanied by 160 plates, many of which contain several 

 illustrations,and a bibliography of publications on the composition of coal. 



An enormous amount of valuable information on the composition of 

 coal has been accumulated in this bulletin. Man> side lights on plant 

 life during the Paleozoic are brought out by the study of the spores and 

 other morphological elements of the coal. Biologic factors like the origin 

 of rootlets and the existence of fungi in Paleozoic times, are revealed. 



There are a number of theories concerning the origin of coal, but we 

 are yet unable to form a conclusive conception of this interesting geo- 

 logical process. Thiessen's paper supplies a great amount of information 



which brings us a step nearer to a satisfactory conception. 



A. C. N. 



Contact-metamorphic Tungsten Deposits in the United States. By 

 Frank L. Hess and Esper S. Larsen. United States Geo- 

 logical Survey, Bulletin 725-D, 1921. 



Of the 5, 000 tons of tungsten concentrates (reckoned as 60 per cent 

 WO3) produced in the United States in 1918, about 1,400 tons was in 

 the form of scheelite (CaW04) from contact-metamorphic deposits. 

 Most of these deposits are along the western side of the Great Basin in 

 California and Nevada but there are scattered deposits near Great Salt 

 Lake and in Arizona, New Mexico, and Oregon. Their development has 

 been recent, the first of the type being discovered in 1908. During the 

 European war most of them were active producers but by 1920 all had 

 lapsed into idleness because of the severity of competition with imported 

 concentrates and richer American ores, combined with the great depres- 

 sion in the steel industry. 



The contact-metamorphic tungsten deposits are nearly all at or near 

 the contact between quartzose igneous rocks, principally granodio- 

 rites, and limestones. In a number of districts the deposits are clustered 

 about several small granite outcrops close together, which suggest the 

 presence of a larger granite body beneath. 



The sihcate minerals are those usual in contact-metamorphic deposits, 

 except that minerals carrying boron appear to be absent and magnetite 

 and hematite are notably rare. 



