I40 The American Geologist. ^'«'"'''»' ^^^i. 
tetrahedral elevation. The deficiency is explained by tiie as- 
sumption of vast subterranean blocks of very light niaterial. 
But that explanation is prohibited in the Russian case, since, 
as Helmert has shown, the deviations of a plumb-line from the 
vertical are inconsistent with the existence of such blocks. In 
reference to the North American case, Helmert has remarked 
that the light subterranean blocks must have descended for sev- 
eral kilometres ; and Alildenhall has shown that no reasonable 
assumption will sufifice to explain the facts. 
It would be too much to claim that geodetical evidence at 
present available proves the tetrahedral theory, for accurate 
data are not yet available for a sufihcient proportion of the 
earth to show whether the major deviations are based on a 
regular plan ; but papers, such as that of !\Ir. E. D. Preston, 
show that geodesists are more inclined to regard the theory 
with favor. It is at least clear that geodesy does not disprove 
the hypothesis, and that some puzzling geodetic anomalies re- 
ceive a simple solution if the theory be true. 
GEOLOGY AXD THE TETRAHEDRAL COIGNS AND EDGES. 
Let us now turn to geology, to see if its evidence as to the 
past history of the world refutes or supports the theory. 
The geological evidence ought to be of especial value, as 
w^e should expect to determine the position of the tetrahedral 
coie^ns on the face of the earth.* 
If the tetrahedral theory be true, the four tetrahedral coigns 
should be areas of unusual stability and strength. Comparison 
of the three meridional land-belts shows that each of them be- 
gins in the north with a vast block of Archean rocks. The Eu- 
rafrican zone, in longitude 20'' E, begins with a block occupy- 
ing Scandinavia, Finland, and Lapland, which Suess has 
termed the "Scandinavian schild." It is an area of great ge- 
ological antiquity, which has long remained above sea-level : 
bands of marine deposits of different ages sweep round it. but 
the block may never have been below sea-level. It has un- 
questionably remained as a solid impassive block, which has 
dominated the whole geological history of northern Europe. 
South of the Scandinavian coign are the transverse east auvl 
western chains of the Alps and the Atlas, with the Mediterran- 
• They were assigned to their geometrical positions by Green, and in the 
nteresting recent tetrahedral volcanic map of M. .Michel-Levy. 
