EARTH S CRUST WASHINGTON". 



311 



the interiors of South America, Africa, and Australia are the conti- 

 nental elevation averages as given by Murray. 



The inner circle is that of the average specific volume (-2^=0.361), 

 and the inner broken line, made up of arcs, is that of the average 

 specific volumes of the portions of the earth's crust radially above the 

 successive small arcs. Specific volumes (the reciprocals of the densi- 

 ties) are used instead of densities because the relations are brought 

 out more clearly and immediately by the parallelism with the eleva- 

 tion graph shown by the former. The arc portions of the specific 

 volume graphs in solid lines are the ascertained averages, while por- 

 tions that are unknown, because of the absence of exposures of 

 igneous rocks or for other reasons, are indicated by dotted arcs, their 

 radial distance being roughly estimated, so far as is possible. These 

 various arcs are connected by radial dotted lines. 



The center of the circles is the locus of the axis, seen from the 

 North Pole, and is at the same time the zero point for the two graphs. 



The graphs show the correspondence between elevation and spe- 

 cific volume so clearly that it is scarcely necessary to go into a detailed 

 description; yet a brief summary of the northern zone may be of 

 interest. This represents the conditions around a zone which ex- 

 tends roughly between 40° and 50° north latitude, varying somewhat 

 north or south so as to include available data and complete the circle. 

 The data on which the graphs are based are given in Table V. 

 Table V. — Average densities, specific volumes, and elevations. 1 



Average 

 elevation. 



Feet. 



+2, 252 



1,888 



2,500 



2,078 



939 



3,189 



2,021 



805 



? 



-12,800 



-15,400 



Earth 



North America. 

 United States. . . 

 South America. 



Europe 



Asia 



Africa 



Australia 



Antarctica 



Atlantic floor... 

 Pacific floor 



ZONE 40°-50° NORTH LATITUDE. 



California 



Oregon and Washington 



Utah and Nevada 



Colorado 



Ozark region 



Michigan, Wisconsin, Minnesota 



Appalachia ( Pennsylvania to G eorgia) 



New England and New York 



Great Britain 



France 



Germany 



Switzerland and Tyrol 



Austria-Hungary 



Urals and Caucasus 



Pamirs 



Japan 



ZONE 10°-20° SOUTH LATITUDE. 



Andes 



East Brazil 



Africa (east and west) 



Madagascar and Reunion 



New Zealand 



+ 3,000 



2,500 



6,000 



7,000 



2,000 



1,000 



2,000 



750 



300 



600 



800 



5,000 



2,0007 



2,000 + 



13,000 



1,420 



6,000? 



2,500? 



2,021 



2,199 



2,134 



' For the hypsometric data I have consulted Murray, Scot, Geog. Mag. iv, pp. 1-29, 1888; Gannett, 

 U. S. Geol. Survey, Am. Rep. 13, ii, d. pp. 283-289, 1892; Bull. No. 274, 1906; and other authorities. 



