224 KECORD OF SCIENCE FOR 1886. 



level but from "small columns shows nearly the same size of crystals 

 with more glass base." Higher up iu the sheet the rock in medium- 

 sized columns " has somewhat smaller feldspar crystals and more glass 

 base, in places brown and giobulitic, with feru-like groups of magnet'te 

 crystals. Midway up the cliff the rock shows still more giobulitic and 

 microlitic glass, and that from 10 feet below the present upper surface 

 has smaller crystals and rather more glass base. The variations from 

 bottom to top of the lava are slight but distinctly noticeable, and indi- 

 cate that the cooling which caused the consolidation of the mass was 

 more rapid at the top than at the bottom, which corresponds with the 

 subsequent conditions deemed necessary to produce the different sys- 

 tems of columnar cracking."* 



102. McCormick discusses the nature of concretions in crystalline 

 rocks and describes in detail those in the granite in Craftsbury, Ver- 

 mont. From a study of the literature of the subject two classes of in- 

 clusions are recognized ; the first are ovoid in structure, seldom sharply 

 defined, and often include nodules. They are believed to be contem- 

 poraneous with the solidificatiou of the enclosing rock mass. The 

 second class are generally angular and very dissimilar from the matrix. 

 In the granite of Craftsbury the inclusions consist of spheroidal nodules 

 of biotite from one- half to two inches iu diameter and often four inches 

 in length, in some cases much flattened and crumpled. Microscopic ex- 

 amination shows the mica to be in concentric layers with scattered grains 

 of quartz, most abundant iu the center. They are very difficultly sepa- 

 rated from the remaining rock, and it is thought that they are masses of 

 biotite and segregated from the original chloritic mass, and that their 

 wrinkling indicates an igneous condition of the granite at the time of 

 their separation. t 



103. Dana I proposes a nomenclature for metamorphism and porphy- 

 ritic structure in rocks. For the former, Grystallinic is suggested for 

 secondary enlargement ; Paramorphic for the results of paramorphism, 

 and Metachemie for the term " metasomatic." In descriptions of por- 

 phyritic structure it is proposed that such terms as Orthophyric, Leu- 

 citophyric, Augitophyric, Quartzophyric, etc., be used as adjectives to 

 indicate at once the structure and the mineral causing it. 



PARAMORPHISM, METAMORPHISM, ETC. 



The writer is compelled to confine his attention to the American con- 

 tributions to this subject on account of lack of time and inaccessibility 

 of the literature. The manj^ questions connected with the formation of 

 crystalline rocks are now being discussed by an increasing number of 

 observers, who, with the aid of misroscopic j^etrography, and with wide 

 opportunities for systematic field survey, obtain results vastly more 



*Ain. Jour. Sci., iii, vol. 3, pp. 321-331 and plate. 

 tPhiladelpliiaAcad. Sci., Proc. (vol. 37), pp. 19-24. 

 I Am. Jour. Sci., ii, vol. 32, pp. 69-72. 



