GEOPHYSICAL LABORATORY. IO7 



(21) Die Sulfide von Zink, Cadmium und Quecksilber; ihre Kristallform und gene- 



tischen Beziehungen. E. T. Allen und J. L. Crenshaw. Mikroskopische 

 Untersuchung von H. E. Merwin. Z. anorg. Chem., 1912. 



(22) Mikroskopische Petrographie vom Quantitativen Standpunkt. Fred. Eugene 



Wright. Neues Jahrb. Min. Geol. (In press.) 



A German translation of "Microscopical petrography from the quantita- 

 tive viewpoint" (Geol., 20, 481-501, 1912). Reviewed under No. 16. 



(23) Study of a contact metamorphic ore-deposit. The Dolores mine, at Matehuala, 



S. L. P., Mexico. J. E. Spurr, G. H. Garrey, and Clarence N. Fenner. 

 Econ. Geol., 7, 444-484. 1912. 



This is a study of an interesting problem in applied geology, toward which 

 the laboratory contributed an exhaustive petrographie investigation of the 

 various types of rock which had been collected in the field. The problem 

 comprised the study and elucidation of the phenomena of an unusual type of 

 metamorphism and ore-deposition, associated with and consequent upon the 

 intrusion of a great mass of eruptive rock into a series of sedimentary beds. 

 In conjunction with the field-work a collection of typical rock-specimens was 

 sent to the laboratory. From these the field relations which had been ob- 

 served were confirmed and supplementary information obtained. From the 

 different sources of information thus made available it was possible to ar- 

 rive at well-grounded conclusions regarding the geological history of events, 

 including the sequence of mineral deposition, the nature of the circulating 

 solutions, and the relations existing between the metallic sulphides and the 

 gangue minerals. 



(24) The various forms of silica and their mutual relations. Clarence N. Fenner. 



Jour. Wash. Acad. Sci., 2, 471-480. 1912. 



The problem presented by the various forms of silica in their relations to 

 each other has been the subject of some previous investigation by a number 

 of experimenters. The results obtained have not been altogether concor- 

 dant, and the present investigation was undertaken in order to reconcile or 

 explain these discrepancies and to throw as much additional light as possible 

 upon the subject. The great abundance of free silica in very diverse modes 

 of occurrence in nature made it appear of some importance to secure such 

 additional information. The investigation is not yet concluded, but the main 

 relations have been established. 



The inversion-point between quartz and tridymite has been located with 

 considerable exactitude (at about 870 ) and the best conditions for effecting 

 the transformation have been determined. It has also been settled that the 

 transformation is reversible. Similar information has been obtained regard- 

 ing the transformation of tridymite into cristobalite (at about 1470 ), and it 

 has been established that the two are perfectly distinct minerals, each with a 

 definite range of stability. It has been determined, however, that under cer- 

 tain conditions one form of silica may be produced within the field of sta- 

 bility of another, and some of the divergent results of previous investigators 

 are thus explained. 



The inversions of a into /? tridymite and a into /? cristobalite have also been 

 studied by somewhat novel methods and the relation of these to the other 

 transformations shown. 



