234: Scientific Intelligence. 



This is in close accord with my views outlined in the paper on 

 isostasy already referred to (this Journal, July, 1921.) On page 

 19 of that article we read : 



"Aside from these changes in the elevation, I do not know of 

 any others which are caused by. isostatic adjustment. They must 

 be due to other causes which, I believe, are decreases and increases 

 of density in the isostatic shell. ' ' 



Again, on page 16, it is stated : "We are led to the conclusion 

 that the cause of the mountain formation is a local one, and the 

 only local cause seems to be a change in density in the column. ' ' 



It is seen from the above that Tandy and I agree as to the 

 probable cause of uplift. We do not hold the same views as to 

 the zone within which the horizontal movement takes place to 

 restore the isostatic equilibrium after erosion and sedimentation 

 have taken place. Tandy expresses the view that: 



"It is considered doubtful if movement is generally possible 

 after depths of 30 miles or so, though in my view this depth will 

 vary greatly according to the activity of the circulation. Beyond 

 this depth, things merge into the condition of the nucleus, which 

 we will provisionally regard as inherently solid, cold, and inert. ' ' 

 This view ignores the geodetic investigations, the results of which 

 indicate in the strongest way that the isostatic compensation must 

 extend to an average depth of the order of 60 miles. Tandy's 

 theory as to the depth within which horizontal movement occurs 

 falls when it is realized that we cannot have isostatic compensa- 

 tion extending far below the zone of flow. 



Under the headings "Crustal Conditions," "Generation of 

 Heat by the Circulation," "Contraction and Expansion" and 

 "Evidence and Examples" Tandy sets the stage for bringing out 

 the main idea of his paper, "The Circulation of the Earth's 

 Crust. ' ' Some of the ideas advanced are good, but most of them 

 are speculative and difficult to accept. He says: 



' ' The whole theory must stand or fall on the principle that the 

 circulation is of the most detailed character, so that every stream 

 and depression in the mountains will be an area of deposit, as 

 already discussed. The highest mountains of the world are all 

 very steep folded mountains, and the avalanches, land-slides, and 

 other erosion down the sides of such mountains must be enormous. 

 So that, if we believe that the great bulk of this deposit is not 

 carried forward, but sinks directly into the beds of the streams 

 and rivers, and finally circulates back, under the adjoining 

 heights and spurs, we at once get a circulation far more powerful 

 and rapid than has hitherto been conceived. ' ' 



At another place the author states, "I also think that the cir- 

 culation in high mountain regions takes place only a few miles 

 below the surface." 



