GEOPHYSICAL LABORATORY. 163 



PUBLICATIONS. 



(386) Tridymite crystals in glass. N. L. Bowen. Am. Mineralogist, 4, 65-66 C1919). 



Crystals of tridymite similar to those described by Le Chatelier in a French 

 glass were found in a specimen of light flint glass. Question is raised regarding 

 Le Chatelier's conclusion that tridymite is the only form of sihca stable at 

 temperatures above the stability range of quartz. Cristobalite forms freely 

 and persists indefinitely above 1470° in glasses capable of precipitating sihca 

 at such temperatures and is therefore the stable phase above 1470°. 



(387) Abnormal birefringence of torbernite. N. L. Bowen. Am. J. Sci., 48, 195-198 (1919). 

 Torbernite from Cornwall was found to have totally different optical prop- 

 erties from those ordinarily assigned to it. Torbernite is usually described 

 as uniaxial and negative with indices 1.592 and 1.582. The present tor- 

 bernite was found to have a mean index of about 1.62 and to give very 

 abnormal interference colors, which are always red, blue, or purple, whatever 

 the thickness of the section. Measurement of the indices co and e for various 

 wave-lengths showed that the mineral has very weak positive birefringence 

 for the red end of the spectrum but is negative for the blue end. For green 

 light of 515/i wave-length it is isotropic. This form of torbernite is the hepta- 

 hydrate or the first stage in desiccation from the dodecahydrate, which 

 desiccation may take place spontaneously. 



(388) Cacoclasite from Wakefield, Quebec. N. L. Bowen. Am. J. Sci., 48,440-442 f 1919). 

 Chemical, microscopic, and crystallographic evidence all points to the fact 



that cacoclasite is a pseudomorph (essentially a paramorph) of grossularite 

 after sarcohte with calcite and apatite filling the voids produced by the re- 

 duction of volume involved in the change. 



(389) Crystallization-differentiation in igneous magmas. N. L. Bowen. J. Geol., 27, 



393-430 (1919). 



In this paper some of the objections which have been raised against the 

 theory of crj^stallization-differentiation are considered; and its adequacy to 

 explain certain phenomena, for which it has been considered to fail, is pointed 

 out. The supposed advantages of liquid immiscibility in explaining discon- 

 tinuous variations are considered, and reasons are given for believing that no 

 such advantages exist. On the basis of crystalhzation, explanations are 

 suggested for discontinuous variations, particularly those noted in the asso- 

 ciation gabbro-granophyre. A suggestion is made as to the origin of primary 

 banding with particular reference to the Duluth lopohth. 



(390) Echellite, a new mineral. N. L. Bowen. Am. Mineralogist, 5, 1-2 (1920). 

 Small spheroidal masses of a radiating fibrous mineral occurring in a basic 



intrusive from Sextant Portage, Abitibi River, Northern Ontario, are found 

 to be made up of a new mineral. The optical properties are a = 1.530; 

 i3= 1.533; 7 = 1.545±.001; -{-; 2V = 50±5. The elongation is /3 and the 

 crystallization probably orthorhombic. Chemical analysis gave the formula 

 (Ca, Na2)0.2Al2O3.3SiO2.4H.iO. The name echellite is proposed for this new 

 mineral in allusion to the stepped (1, 2, 3, 4) ratios. 



(391) Differentiation by deformation. N. L. Bowen. Proc. Nat. Acad. Sci., 6, 159-162 (1920). 

 An examination into the tendency of deformation of a partly crystalUzed 



igneous magma toward the separation of hquid from crystals and the conse- 

 quent production of a differentiated mass. An effect of this kind is beheved 

 to be a factor of importance in the production of discontinuous differentiation, 

 of monomineralic types, of complementary dikes, and of primary banding. 



