Makch 24, ]9n] 



SCIENCE 



465 



Therefore, it has been assumed that temperatures 

 approximating fusion conditions would be found 

 at about twenty miles depth, but such computa- 

 tions ignore the effects of radioactivity on the 

 geothermal gradient. Therefore the subject needs 

 reexamination in light of new data. 



A study of the subject leads to the conclusion 

 that radioactivity supplies not less than one sixth 

 nor more than one half of the annual heat loss of 

 the earth. It appears, further, that this source 

 of supply of heat must be largely concentrated 

 near the surface of the earth. Therefore, the 

 actual temperature gradient within the earth can 

 not be approximately a straight line, as derived 

 from the laws of cooling, but must curve con- 

 stantly and at a rate which depends upon the 

 amount of heat produced withia the earth by 

 radioactivity at various depths. After making 

 due allowance for the effects of radioactivity and 

 cooling upon the geothermal gradient it appears 

 that temperatures approximating fusion condi- 

 tions are to be expected at a depth of about thirty 

 miles instead of twenty miles. Further, it appears 

 that if radioactivity supplies much more than 

 about one quarter of the annual heat-loss of the 

 earth the nebular hypothesis as ordmarily under- 

 stood must be incorrect. 



Finally (as pointed out by Becker), by making 

 proper allowance for the eifeet of radioactivity, 

 Kelvin 's estimate of the age of the earth is 

 brought into harmony with the best estimates 

 derived from other sources, instead of standing as 

 heretofore, as a perpetual challenge to the accu- 

 racy of other estimates. 



Terrestrial Deposits of Owen's Valley, California: 



Arthur C. Tkowbkidue. 



Alluvial deposits occur, as fans and piedmont 

 alluvial plains on either side of Owen's Valley, 

 Cal. On the Sierra side the deposits are fluvio- 

 glacial. At the foot of the Inyo Mountains there 

 are deposits of two ages. The materials range 

 in size up to bowlders thirty feet in diameter. 

 They are sorted roughly into lenses and pockets. 

 The fans are now being dissected. The cause of 

 deposition is decrease in velocity and volume of 

 streams from the mountains. 



Huge bowlders are transported in the following 

 manner: The stream moves fine material from in 

 front of the bowlder and piles other material 

 behind it. As the bowlder is undermined it falls 

 over into the depression. This process is repeated 

 time and again, resulting in periodic motion for 

 the bowlder. 



Dissection has followed great fluvio-glacial de- 

 posits on the surface of the fans, these deposits 

 bearing relations to present conditions similar to 

 those between a valley train and normal stream 

 erosion. 



Criteria are presented for the distinction of 

 such deposits from still water deposits. 

 Note on a Metliod in Teaching Optical Mineral- 

 ogy: F. W. McNaie. (To be published in Am. 



Jour. Science.) 



In the effort to condense optical mineralogy, the 

 form of the wave shell and deductions therefrom 

 have been rested as directly as possible upon the 

 so-called reciprocal ellipsoid of McCullough. If 

 one may judge by the text-books, the ellipsoid, 

 whether that of Fresnel or this of McCullough, is 

 used in the non-mathematical presentations of the 

 subject to obtain the wave shell or its three prin- 

 cipal sections, and is then immediately abandoned. 

 The device, which occurred to me some years since 

 and which I have found useful in obtaining re- 

 sults with my students, is to carry the use of the 

 ellipsoid into a considerable number of the appli- 

 cations of the theory to the properties of crystals. 

 Perhaps the most conspicuous example of its use- 

 fulness lies in its application to the distinction 

 between positive and negative crystals in con- 

 vergent polarized light. Details can not be ab- 

 stracted. 



Its justification rests in the readiness with 

 which a student who once comprehends the mean- 

 ing of the ellipsoid becomes independent in his 

 application of the test of the quartz wedge, apply- 

 ing the wedge in either position and reasoning out 

 his results with an assurance of correctness. 

 Indications of a Euronian Continental Angle: H. 



B. Ayees. 



A belt of Huronian beds will probably be found 

 parallel to the Eocky Mountains through the 

 Dakotas, Alberta and northwestward, forming a 

 continental angle with the Minnesota belt prob- 

 ably in the vicinity of the Black Hills. A few 

 outcrops of quartzite and slates and some topo- 

 graphic and drift data supply the foundation for 

 the conjecture. 

 The Dam Lahe Quartzite: H. B. Ayees. 



The quartzite of Dam Lake (Aitkin County, 

 Minn.) has been explored by drilling through both 

 contacts with adjoining rock and the results prove 

 it to be the equivalent of the Pokegama quartzite, 

 and here overlying the Keewatin formation. 



