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SCIENCE. 



[N. S. Vol. XXV. No. 642 



meager and inconclusive. In any case, the 

 hypothesis fails to account for basic stocks in 

 highly siliceous rocks. 



Referring to stocks and batholiths which he 

 had studied, Mr. Cross stated that they testi- 

 fied rather to violent and powerful ascensive 

 forces back of the magmas and expressed the 

 belief that in such masses, as in laccoliths, 

 the coming to place of the magmas was in 

 first degree a mechanical displacement of the 

 invaded rock, as such. 



Mr. G. F. Becker considered the intrusive 

 magmas from a physical and chemical stand- 

 point and emphasized his view that such 

 magmas are emulsions rather than liquids; 

 that, at the time of intrusion, they consist 

 largely of crystal aggregates with a small 

 amount of interstitial material not yet crystal- 

 lized — a fact evident from the mutual inter- 

 ference and simultaneous crystallization of 

 the components of any deep-seated rock. 

 This state was compared to that of partially 

 melted snow which consists of ice crystals 

 with some free water; in short, the magma 

 at the time of intrusion is a soft solid like 

 modeling clay and the intrusion must there- 

 fore follow different laws from those of an 

 intrusive fluid. In particular he pointed out 

 that semi-solid magmas may support masses 

 of relatively large density. The presence of 

 aplites and pegmatites in granular intrusives 

 and not in porphyries is significant in support 

 of this theory of the soft solid condition of 

 deep-seated intrusive magmas. 



Mr. A. L. Day directed attention particu- 

 larly to the physical conditions which must 

 be reckoned with in formulating the stoping 

 hypothesis. 



1. The wall rocks in these cases must be 

 accounted very good conductors of heat. It 

 is, therefore, difficult to conceive of a sharp 

 temperature difference between the intruding 

 mass and the wall rock existing for more than 

 a very short interval of time, whatever the 

 relative masses involved. If the amount of 

 heat to be distributed is large, active resorp- 

 tion must occur; if small, adjacent layers of 

 the intruding mass will very soon become solid 

 or hyperviscous. 



2. The evidence which has been gathered by 



the Geophysical Laboratory points persistently 

 to the extreme viscosity of all the highly 

 siliceous minerals and mixtures, even at tem- 

 peratures far above their melting points. 



3. There is a very reasonable probability 

 that most crystalline rocks are more dense at 

 the melting temperatures than the liquids 

 which they form, but it will be remembered 

 that Professor Barus's experimental proof was 

 confined to the gradual transition from liquid 

 to amorphous glass, and therefore leaves the 

 important question still open. 



Mr. Andrew C. Lawson criticized Daly's 

 hypothesis from the point of view of the great 

 diameter of certain batholiths and the flatness 

 of the arch roofing them. With a span of 

 100 miles or more, if the roof were specifically 

 heavier than the invading magma, he did not 

 see what would prevent its complete founder- 

 ing. Eeferring to the high viscosity of the 

 feldspars and quartz, as determined by Dr. 

 Day's experiments, he indicated that, while 

 this was a property of the individual crystals, 

 it did not finally prove that mixtures of such 

 materials in magmatic fusion with other con- 

 stituents of granite would be so highly 

 viscous. Dr. Becker had drawn the con- 

 clusion that porphyritic structures could only 

 be developed in fluids of high molecular 

 mobility. Now the granite rocks of the High 

 Sierra were highly porphyritic over a wide 

 extent. The large well-formed crystals of 

 orthoclase, commonly over an inch in length, 

 showed that in that great batholith the magma 

 had not been highly viscous. Moreover, these 

 porphyritic orthoclases were chiefly aggre- 

 gated in the upper levels of the batholith as 

 if they had been assembled there by flotation 

 from the lower levels, again indicating ab- 

 sence of high viscosity. Further, the granite 

 of the Sierran batholith swarms with angular 

 inclusions. These are not fragments that had 

 been torn from the roof and caught in process 

 of sinking. They are mineralogically allied 

 to the lamprophyres, and represent fragments 

 derived from the shattering of deep-seated 

 masses ascending with the upwelling of the 

 batholithic magma. These facts all indicate 

 fluidity. The speaker had, however, been one 

 of the first to argue for the high viscosity of 



