262 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
getically folded, dislocated and elevated in the Tertiary epoch, at the time of 
the formation of the principal existing mountain chains, including within 
themselves, with two or three doubtful exceptions, nearly all the seismic regions, 
which in consequence characterize them. 
The folded architecture of the geosynclines is unstable, in contrast to the 
tabular architecture of the eontinental areas, and this has with much prob- 
ability been true of all the geological epochs.® 
We have here, then, a very clear statement that the earth’s two 
zones of earthquake of the present time, including together as they 
do 94.62 per cent of all recorded earthquakes upon the land areas, 
are the zones within which the thickest lenses of sediments were 
deposited during the Mesozoic era, and where also, beginning in 
late Cretaceous or Tertiary time, ranges of mountains have been 
in process of erection. It is further pointed out that this zone of 
folding is much dislocated. 
ADJUSTMENTS WITHIN A FAULT MOSAIC AS COROLLARY TO MOUNTAIN 
GROWTHS 
Tarr and Martin, 1906.—In 1899 Thoroddsen printed in the “ Ice- 
landic Language” an account of the earthquakes which occurred in 
Southern Iceland in 1896, and in which five separate earthquakes 
had shaken in succession each of five contiguous earth blocks. In 
1906 Tarr and Martin * clearly demonstrated that the earthquake of 
1899 along the base of Mount St. Elias was a renewal of mountain 
growth along the shore of the Yakutat Bay in which large vertical 
adjustments measured in ten’s of feet took place between the large 
blocks within a fault mosaic, and that movements of smaller magni- 
tude occurred between smaller blocks which were parts of the larger 
and composite ones. This study is therefore one of the most impor- 
tant and satisfactory that has ever been made of a great earthquake. 
Hobbs, 1907—In 1905 the writer carried out a comprehensive 
study of the great Calabrian earthquake of that year with the result 
of showing that even where actual faults are not disclosed by 
escarpments or other displacements at the surface of the ground, 
their course may be followed often in great numbers as seismotec- 
tonic lines—lines of heavy shock. These lines, as the examination 
5. de Montessus de Ballore, ‘‘ Les Tremblements de Terre,” Géographie Séismologique, 
Colin, Paris, 1906, pp. 24—25. 
®@A German abstract of Th. Thoroddsen’s paper appeared in vol. 47 (1901) of 
Petermann’s Mitteilungen. 
7™R. S. Tarr and L. Martin, “Recent changes of level in the Yakutat Bay Region, 
Alaska,” Bull. Geol. Soe. Am., vol. 17, May, 1906, pp. 29-64, pls. 12-23. 
8 William Herbert Hobbs, “On some principles of seismic geology, with an introduction 
by Edward Suess,” Gerlands Beitriige zur Geophysik, Leipzig, vol. 8, 1907, pp. 217-292, 
pl. 1, and 10 figs. “The geotectonic and geodynamie aspects of Calabria and northeast- 
ern Sicily, a study in orientation, with an introduction by the Count de Montessus de 
Ballore,” ibid., pp. 293-362, 10 pls. and 3 figs. 
