296 



SCIENCE. 



[N. S. Vol. XVII. No. 425. 



The hour being late there was no discus- 

 sion and the separate section adjourned. 



On reassembling Wednesday morning 

 the following two papers were delivered 

 together. 



Studies in the Grain of Igneous Intrusives: 

 Alfred C. Lane, Lansing, Mich. 

 In studying the genesis of minerals from 

 an igneous magma, the importance and in- 

 terest of studying specimens at various 

 known distances from the margin will be 

 illustrated by particular instances. Slides 

 of chips taken at known distances from the 

 edge of flows were passed around, and even 

 to the unaided eye the increase of coarse- 

 ness toward the center was marked. The 

 subject was then treated mathematically in 

 connection with diagrams and with the 

 next title: 



On the Porphyritic Appearance: Alfred 



C. Lane, Lansing, Mich. 



There are some five different kinds of 

 phenocrysts, or crystals, which may give a 

 porphyritic appearance, to wit: 



Coarser relics of a previous consolida- 

 tion. 



Crystals whose formation took place dur- 

 ing the migration of the igneous magma. 



Crystals which were formed early in the 

 process of cooling and solidification, so that 

 their grain continues to increase clear to the 

 center, while later formed constituents in- 

 crease only for a shorter distance from it, 

 their grain thereafter remaining uniform. 

 This porphyritic type will be most obvious 

 at the center of the igneous mass. 



Crystals, the conditions (temperature) 

 of whose formation were nearly half way 

 "between those obtaining initially in the 

 igneous magma and the country rock. Such 

 ■crystals will be most conspiciiously por- 

 phyritic at or near the margin. 



Finally there may be crystals which, 

 like the staurolite of schists, are formed by 

 metamorphic actions, of secondary origin, 



and occur in sediments, and only casually 

 occur in igneous rocks. 



Attention is particularly called to the 

 third and fourth classes, the possibility of 

 the existence of which has been almost over- 

 looked, though their possible existence may 

 be readily inferred from inspection of 

 diagrams of- the cooling of an intrusive. 

 Certain field observations render their 

 actual existence probable. 



A Plumose Diabase containing Sidero- 

 melan and Spherulites of Calcite and 

 Blue Quartz: B. K. Emerson, Amherst, 

 Mass. 



The paper gave a description of an ex- 

 tensive series of specimens of coarsely 

 porphyritic diabase possessing feathery 

 pyroxenes several inches long, and much 

 very easily soluble tachylite or sideromelan, 

 together with spherulites of calcite and this 

 glass, or of deep cobalt-blue glass, radiating 

 from a point near the border. The whole 

 is thought to have been caused by the in- 

 draught of much calcareous mud, its solu- 

 tion in the magma and recrystallization. 

 Many specimens were passed from hand to 

 hand in illustration. 



Shifting of Faunas as a Problem of Strati- 

 graphic Geology: Henry S. Wil^/IAms, 

 New Haven, Conn. 



A comparison of sections through the 

 upper and middle Devonian rocks of the 

 New York-Pennsylvania province discloses 

 marked differences in the faunas occurring 

 at corresponding levels. These facts were 

 presented and their explanation found in a 

 shifting of faunas during the time repre- 

 sented. The nature, extent and mode of 

 recognition of faunal shifting in studying 

 stratigraphy were discussed, and some con- 

 clusions, suggested by the facts, were drawn 

 as to the desirable modification of custom- 

 ary practices in correlating formations by 

 their fossils. 



The sections, eight in number, extended 



