ABSTRACTS OF PAPERS 61 



under the chainnaiiship of Vice-President Wasliington and with E. (). 

 Hovey as Secretary. 



TITLES AND ABSTRACTS OF PAPERS OF GROUP A AND DISCUSSIONS THKRllON' 



CONTRIBVTIOX TO THE HYPOTHESIS OF MOUNTAIN FORMATION 



BY E. C, ANDREWS 



Read l)y title. 



EARTH'S CRUST AND ITS EVOLUTION 

 I5Y REGINALD A. DALY 



(Ahstract) 



According to records at deep borings, the mean increase of temperature with 

 depth seems to be less rapid in eastern North America tlian in western and 

 central Europe. In eacli continent tlie rate of temperature increase itself in- 

 creases with depth, at least to the depth of 2,000 meters. Deeper down the 

 acceleration doubtless falls to zero and changes sign, but it appears already 

 clear that extrapolation from the average surface gradient is not likely to 

 give a temperature too high at a depth of the order of 40 kilometers. At that 

 depth, therefore, a temperature of 1,200° centigrade or more may be expected. 

 At that temperature and corresponding pressure, ordinary rock-matter can not 

 be crystalline. 



Angenheister's recent study of seismograms has led him to estimate the 

 thickness of the crust under the Pacific as about 41 kilometers, and that of 

 the crust under the surface of Eurasia as about 28 kilometers. 



Thus, from two lines of evidence the conception of a thin, solid crust on a 

 non-crystalline, elastico-viscous substratum seems justified and consonant with 

 the facts of geophysics in general, as well as with a sound cosmogony. 



That the density of the sub-Pacific crust is greater than the density of the 

 underlying layer is a necessary conseciuence : hence an important condition 

 for the instability of the crust in past time. 



These conclusions may guide speculation as to the development of the crust 

 in its present form. Rased on the general idea in the Taylor- Wegener hy- 

 pothesis of the horizontal movement of continents, a theory of the continents 

 and ocean-basins will be sketched. This theory includes an explanation of the 

 segregation of the earth's salic material in one hemisphere : the intense defor- 

 mation of the Precambrian formations; the Postcambrian fragmentation of 

 the primitive continent and the associated mountain-building. 



Presented extemporaneously. 



DlSCf.SSlON 



Prof. W. H. HoBBs: As I have listened to Professor Daly's paper T have 

 thought if he were not such a brilliant geologist what a fine trial lawyer he 

 would be. I have been impressed not with the inadequate attention the 

 Wegener theory has received, but rather with the exaggerated attention that 



