Reviews — Petrographic Methods. 381 



becomes very pronounced and striking. The optical properties of this 

 mineral show some relationship to scorodite, strengite, and phosphorite. 

 Its crystallography and chemical composition are also discussed, and 

 a typical nodule and a crystalline aggregate, with tabular crystals, 

 are figured on the plate. 



Campiosatjrus. — jS'o. 1878 of the same volume (pp. 687-96, with 

 plates Iv-lxi) contains the description of two unusually perfect 

 skeletons, the types of Camptosaunts nanus, Marsh, and C. browni, 

 Gilmore, that have been mounted for exhibition in the United States 

 National Museum. The specimens formed part of the Marsh 

 Collection and were obtained fi'om the well-known "Quarry 13", 

 near Como Bluff, Albany County, Wyoming. Both stand on a base 

 of artificial matrix representing the sandstone in which they were 

 found, the larger ( C. browni) being in quadrupedal position, the 

 smaller ( C. nanus) in bipedal pose and representing a rapidly walking 

 animal with head thrown forward, the right leg at the end of 

 a forward stride, and tail doubly curved and slightly lifted. Some 

 correction of Marsh's earlier restoration has been made, and in the 

 case of C. browni a better-balanced animal has been produced by the 

 shortening of the presacral region. The mounting represents nearly 

 the whole length of the toes (except the first) as touching the 

 ground, on account of the fact that certain footprints show nearly the 

 full length of the phalanges. The position in which the bones of 

 G. browni were found is shown in a map, and there are also six plates 

 reproducing photographs of the mounted skeletons. 



IX. — Petrographic Methods. By Professor Dr. Ernst Weinschenk: ; 

 rendered into English by R. W. Clark. 8vo; pp. xvii + 396. 

 JS'ew York and London : McGraw-Hill Book Company, 1912. 

 Price 15s. 



rpHE title Petrographie Methods includes the translation into English 

 X of two books. Die Atileitunff zum Gebrauch des Polarisations- 

 mihroshops and Die Gesteinsbildenden Mineralien. The first, on the 

 polarizing microscope, appeared in the third edition in 1910, and the 

 second, on the rock-forming minerals, in the second edition in 1907. 

 Both books were then revised, and the work before us is therefore of 

 considerable value to English students of petrology. 



The necessity of a thorough knowledge of the fundamental 

 principles of microscopic optical methods in petrology is fully 

 realized in the first part of this book. The discussions on lenses 

 and on polarized light are very clear, and several polarizing micro- 

 scopes (chiefly hj German and American makers) are described. 

 Methods of adjustment and investigations in ordinary and in polarized 

 light are fully dealt with. The use of accessory devices (rotation, 

 heating, and projection) for special investigation is considered in a 

 less detailed manner in the appendix. 



In the second part 139 pages are devoted to the description of 

 106 rock-forming minerals; and preceding these are useful accounts 

 of chemical and physical methods employed in separation and 



