July 24, 1896.] 



SCIENCE. 



119 



marine beds of the Trias. Such are known in 

 the Alps, Himalayas, Salt Eange of India, 

 Siberia and western North America. Quite 

 recently the Vienna geologists, Drs. Mojsisovics, 

 Waagen and Diener have proposed a classifica- 

 tion of the Marine Trias. Four series are 

 recognized, the Scythic, Dinaric, Tirolic and 

 Bajuvaric. These are divided into stages, sub- 

 stages and zones. In the present paper the 

 author attempts to show the relations of Amer- 

 ican marine strata to those of Europe and 

 Asia on the basis of the , above classification. 

 He concludes that the Alps cannot longer be 

 said to furnish the typical region even for ma- 

 rine Trias, but that each region of the earth 

 has some open sea development of a stage 

 lacking elsewhere. Hence studies in faunal 

 geography must be combined with those in 

 phylogeny. 



The Geology of the Little Bocky Mountains : By 

 Walter Harvey Weed and Louis Y. Pirsson. 

 The Little Rocky Mountains of northern Mon- 

 tana are far removed from the Rocky Mt. Cor- 

 dillera. They are formed by a dome-shaped 

 uplift exposing Archean and Paleozoic rocks in 

 a region of horizontal Cretaceous strata. They 

 represent on a smaller scale the kind of phe- 

 nomena we have in the Black Hills uplift as 

 described by Russel in a former number of the 

 Journal. The nucleal core is of crystalline 

 schists, but the structure has been modified by 

 the intrusion of a great laccolitic mass of granite 

 porphyry. The schists are thought by the 

 authors to be Archean. Above these are shown 

 beds of Cambrian, Silurian, Devonian, Jurassic 

 and Cretaceous. Petrographic study of the 

 prophyry shows it to belong to the alkali 

 granite-syenite series. It is very poor in lime 

 magnesia and iron. The magmas resemble 

 those of the other detached mountain groups of 

 Montana. Ores bearing both gold and silver 

 are found associated with flourite in the altered 

 porphyry. The occurrence of telluride ores 

 is much the same as at Cripple Creek. In 

 most of the ores free gold is found in spongy 

 masses of dark copper color. The Goldbug 

 mine is the only property which shows much 

 development, and this is being prospected now. 



Schistosity and Slaty Cleavage : By George F. 

 Becker. The idea developed in the paper is 



that the deformation of a solid, homogeneous 

 viscous, isotropic, not infinitely brittle mass 

 will develop structures in it on not less than 

 one surface, nor on more than four surfaces 

 simultaneously. These structure surfaces will 

 in general stand at acute angles to the direction 

 of the pressure to which they are due, and the 

 flattening of the strain ellipsoids will not be 

 normal to the pressure save in a limiting case. 

 The common theory of slaty cleavage is well 

 known. 



The author presents evidence that solid flow 

 does produce cleavage which is parallel to the 

 lines of relative tangential motion or gliding 

 and that this need not be accompanied by rup- 

 ture, however microscopic. He thinks that no 

 closer approach to slaty cleavage can be gotten 

 by flattening of the particles even in a weak 

 matrix than is gotten in natural sandstones, for 

 in these there is approximate parallelism of 

 the grains of quartz and mica scales with the 

 bedding. 



Deformation of Rocks, III.: By C. R. Van 

 HiSE. In this paper schistosity and cleavage 

 are discussed mainly. After defining the terms 

 and referring to the literature of the subject 

 the author lays down and supports the follow- 

 ing propositions. (1) Rock cleavage is due to 

 the arrangement of mineral particles with their 

 long axes or readiest cleavage in a common 

 direction and that this is caused by parallel 

 development of new minerals, by flattening 

 and parallel rotation of old and new min- 

 eral particles and by flattening and parallel 

 rotation of random original particles. (2) 

 The secondary structure of a rock deformed 

 by plastic flow develops in the plane nor- 

 mal to the greatest pressure and is true cleav- 

 age. (3) In heterogeneous rocks having cleav- 

 age, in a soft layer the cleavage more nearly ac- 

 cords with bedding than it does in a hard layer. 

 (4) Upon opposite sides of an anticline cleavage 

 usually diverges downward, while on opposite 

 sides of a syncline it usually converges down- 

 ward. (5) In regions of overturned monoclinal 

 folds the cleavage may be rotated in the same 

 direction throughout, and hence be monoclinal. 

 (6) Fissility developed in the shearing planes is 

 usually secondary to cleavage developed in the 

 normal planes. 



