928 



SCIENCE. 



[N. S. Vol. IV. No. 103. 



mills. In the middle of it is to be observed a 

 distinct schistose structure. 



Mr. Edw. Goldsmith described a similar de- 

 posit two miles north of that referred to. The 

 masses of the rock which had been mined are 

 so resonant as to merit the name gabbro-phono- 

 lite. 



Mr. H. A. Pilsbry described a collection of mol- 

 lusks obtained by himself and Mr. C. W. Johnson 

 in Florida in 1894. Their main object had been 

 to determine the i-elation of existing mollusks 

 to those of the shell heaps, Vivipara georgiana 

 was one of the commonest of the latter, asso- 

 ciated with Unio and AmpuUaria. Certain forms 

 of V. georgiana from the shell heaps have the 

 spire extremely high. He had called this 

 variety altior. The distribution of this form 

 was indicated as being confined to a short 

 stretch of the River St. John's. 



He believed that the shell heap Viviparas be- 

 longed to a race which is now extinct. Another 

 variety of Vivipara from the same region was 

 extremely flattened and broadly shouldered. 

 This he had called limnothauma. He consid- 

 ered its peculiarity a mechanical result of an 

 acceleration of the reproductive process. This 

 form is also extinct, although some were found 

 more recent than those of the mounds. The 

 characters of both these varieties had appeared 

 during the human period. 



AmpuUaria depressa was found in the mound 

 three times the size of the living shell. The 

 Unios did not vary. Edw. J. Nolan, 



Secretary. 



BIOLOGICAL SOCIETY OF WASHINGTON. 267TH 

 MEETING, SATURDAY, DECEMBER 5TH, 



The evening was devoted to the address of 

 the President, Surgeon General Geo. M. Stern- 

 berg, who spoke of ' The Malarial Parasite and 

 other Pathogenic Protozoa.' 



F. A. Lucas, 



Secretary. 



NORTHWESTERN UNIVERSITY SCIENCE CLUB. 



At the November meeting Prof. Jos. P, 

 Iddings presented the topic ' Petrology as re- 

 lated to other branches of Natural Science.' 

 The outline of his address was as follows : 



Petrology deals with theories regarding the 

 origin and formation of rocks, as well as the 



facts of their existence, and the alteration they 

 may undergo. From geology, as generally de- 

 fined petrology derives data concerning the oc- 

 currence of rock bodies as part of the earth's 

 crust ; establishing their formal and quantita- 

 tive relations, and also their age and time rela- 

 tions. It also derives from geology conceptions 

 of their sources and of the processes of their 

 formation and alteration in general terms. 

 Petrology contributes to geology conceptions of 

 the possible condition of the interior of the 

 earth and of its constitution, and also of the 

 processes of molecular change taking place 

 within it. 



From mineralogy petrology derives data 

 cencerning the form, constitution and composi- 

 tion of the mineral components of rocks, which 

 furnish the internal evidence regarding the 

 mode of formation of and the mechanical and 

 chemical changes that take place within rocks. 

 Microscopical study of rocks involves intimate 

 knowledge of geometrical and physical crys- 

 tallography. While research into the nature 

 and crystallization of igneous rocks necessitates 

 excursions into the realm of molecular physics 

 and chemistry ; having to do with the physics 

 of molten rock magmas, and their behavior as 

 solutions in which the dissolved salts are in 

 various molecular conditions, and are capable 

 of diffusion and differentiation. Saturation and 

 crystallization from solution must also be con- 

 sidered, together with the formation of simple 

 and of mixed salts. Chemistry is also called 

 upon to furnish a means of analysis, and to 

 explain processes by which many mineralogical 

 alterations take place. While physics further 

 supplies the laws controlling the transportation 

 and deposition of sediments, and the concep- 

 tions of rigidity and plasticity, of stress and 

 strain, of fracturing and shearing that consti- 

 tute factors of dynamic metamorphism. 



To biology petrology is indebted for data re- 

 garding the source of material forming certain 

 kinds of rocks. But the processes of growth 

 in the biologic kingdom and those in the min- 

 eral realm are strongly contrasted, and the 

 character of an organism and that of a crystal 

 are totally different. A. E. Crook, 



Secretary. 



Evanston, III. 



