842 



SCIENCE 



[N. S. Vol. XXXIX. No. 1014 



The last words that can be made out of the re- 

 maining text are: 



He protects' thee from death 



And an evil fate. 



This foundation Enzu laid, 



Tappinu-grain he makes abundant, 



Thy land he protects, he establishes for men. 



FKIDAT EVENING, APEIL 24 



deception from 8 to 11 o'clock 

 at 

 Mall of the Historical Society of Pennsylvania, 

 S. W. Corner of Locust and Thirteenth Streets 

 Arthur L. Day, Ph.D., director of the geophysical 

 laboratory of the Carnegie Institution of Wash- 

 ington, gave an illustrated lecture on ' ' Some Ob- 

 servations of the Volcano Kilauea in Action," at 

 8:15 P.M. 



SATDBDAY, APRIL 25 



Executive Session — 9:30 o'clock 

 Stated Business. — Candidates for membership 

 balloted for. 



Morning Session — 10 o'clock 

 William B. Soott, Sc.D., LL.D., Vice-president, 

 in the chair. 



Primary Cambrian Manganese Deposits of New- 

 foundland: Nelson C. Dale. (Introduced by 

 Professor W. B. Scott.) 

 Geology of the Wabana Iron Ores of Newfound- 

 land: Albert O. Hayes. (Introduced by Pro- 

 fessor W. B. Scott.) 

 Sewettite, Metahewettite and Pascoite, Hydrous 



Calcium Vanadates: W. F. Hillebrand. 

 The Relations of Isostasy to a Zone of Weakness — 

 the Asthenosphere : Joseph Barrell. (Intro- 

 duced by Professor Charles Schuchert.) 

 The mass of every mountain or mountain range 

 tends to deflect the plumb-line toward it and 

 slightly away from the true vertical, so that the 

 measured latitude and longitude of any locality 

 will differ slightly according as it is determined 

 by triangulation from other regions or by inde- 

 pendent astronomic determination of the point in 

 which the observed vertical pierces the celestial 

 sphere. But Hayford has shown that the deflec- 

 tions of the vertical are actually only one tenth of 

 the deflections calculated as due to the terrestrial 

 relief. This is a quantitative test of the degree 

 of isostasy and shows that the continents stand 

 high above the ocean floors because they are under- 

 laid with lighter matter. Such a relation of den- 

 sity to relief explains the almost complete neutral- 

 ization of the gravitative effect of the relief and 



accounts for the smallness of the observed deflec- 

 tions of the vertical, averaging for stations in the 

 United States only about three seconds of arc. 

 Dynamically it implies a state of flotation of the 

 crust upon the inner earth analogous to the flota- 

 tion of an iceberg in the ocean. 



Yet the earth as a whole is known to be about 

 as rigid as steel; the nature of earthquake vibra- 

 tions transmitted through the earth shows it to be 

 solid throughout and more incompressible and 

 rigid at great depths than near the surface. 

 Within the limited range of temperatures and 

 pressures open to experiment Adams has added to 

 the evidence and shown that rooks possess greatly 

 increased strength under cubic compression. 

 Furthermore, the writer has published recently 

 some calculations which show that the loads sup- 

 ported by the strength of the crust are much 

 greater than had been generally supposed. The 

 delta built out by the Niger Elver, for example, is 

 equivalent in mass to at least 2,000 feet of rock 

 above sea-level, extending over a circular area not 

 less than 300 miles in diameter. 



How then shall the geodetic evidence pointing 

 toward a general flotation of the crust near to 

 equilibrium be reconciled with this other evidence 

 of great rigidity and strength? It has long been 

 supposed that a mobile zone may explain the ap- 

 parent contradiction, but the necessity of postu- 

 lating such a zone becomes greater as the accumu- 

 lated evidence of weakness, on the one hand, of 

 strength, on the other, diverges more and more. 

 It is the consideration of the depth and physical 

 nature of this zone which is the thesis of the pres- 

 ent paper. 



By means of a study of the area of the surface 

 loads and their degree of departure from isostatie 

 equilibrium this zone is located far deeper than 

 other estimates have placed it; the level of mini- 

 mum strength being thought to lie as much as 150 

 to 200 miles deep. The maximum strength is prob- 

 ably at a depth of 10 to 20 miles and falls off 

 rapidly below. At great depths the earth is 

 doubtless again much stronger and resists deform- 

 ing stresses as would a globe of steel. In physical 

 character this zone of weakness is thought to pos- 

 sess high elasticity, but, under prolonged stresses 

 a low elastic limit. This shell of the earth plays 

 such an important part in geologic dynamics that 

 it is thought to merit a special name — the sphere 

 of weakness — the asthenosphere. 



Evidence for a Pulsational Change of Climate in 

 the Libyan Desert: William H. Hobbs. 



