NORMATIVE DENSITIES AND ALTITUDES . 395 



chemical average of Utah-Nevada, however, is based largely on analyses 

 of decidedly silicic (and therefore light) rocks from mining regions and 

 does not truly represent the very extensive areas of less silicic rocks which 

 form much of the area, while the average for Colorado is one of the most 

 satisfactory that we have. Similarly, the density for Russia is the great- 

 est shown by Europe, much greater than those of areas which are lower 

 or of about the same altitude, as Great Britain, Germany, Algonkian re- 

 gion, Missouri-Texas, and British Guiana. This is doubtless because this 

 large area is represented almost exclusively by analyses of the very "basic" 

 (and therefore heavy) rocks of the Urals, described by Duparc, while 

 there are few analyses of the many granitic rocks of Eussia. Bal&ania 

 (including Greece and the archipelago) seems to be lighter than it should 

 be from its altitude, chiefly because the analytical data include few or 

 none of the numerous gabbros and diorites of the region, but are confined 

 mostly to the lighter and more silicic lavas of the volcanoes. New Eng- 

 land (and New York), with a much lower altitude than Appalachia, has 

 about the same density. This correspondence in density may be ac- 

 counted for by the fact that the New England region is comagmatically 

 a continuation of the Appalachian, as is shown by the similar characters 

 of the granitic and other rocks, while the divergence in altitudes may be 

 ascribed to differences in local tectonic movements. Greenland and Spain 

 appear to be much denser than their altitudes would warrant, but this is 

 unquestionably because the analyses which represent these regions are all 

 of rocks on or near the low-lying coastal borders. In the case of Spain, 

 at least, we know that the high interior plateau is composed largely of 

 granites, of which we have not a single analysis. Antarctica presents the 

 same peculiarity as do the two areas just mentioned. The Algonkian 

 region (about Lake Superior) seems to be slightly heavier than it should 

 be for its altitude, probably because of the few analyses of the somewhat 

 abundant granitic rocks of the region. On the other hand, the Oregonian 

 region should be probably rather denser than is shown here, because there 

 are relatively few analyses of the extensive basalt flows. 



The general relations are shown in figures 1 and 2, in both of which 

 the loci for rocks without water are indicated by dots, while those for 

 water-bearing rocks are indicated by crosses, a solid curve corresponding 

 to the former and a dashed curve to the latter. The numbers correspond 

 to those of the areas in Table III. 



In figure 1 are presented the data for only the continents and ocean 

 depths, with the l^perbola 17 connecting the calculated loci for the conti- 



17 The line is a hyperbola if we plot (as we do here) with h and 8 as variables ; it 

 will be a straight line if plotted with d and hd 



