CAUSE OF EARTHQUAKES—HOBBS 275 
Postglacial faults.—Evidence is at hand that faults have been an 
accompaniment of the epeirogenic movements which have been going 
on within this region. The continental glaciers which in the yester- 
day of geology covered the region, planed the rock surfaces to a 
freshly polished condition upon which any subsequent displacement, 
even though of small measure, must be revealed whenever diligently 
sought for. No such search has been generally made, but already a 
considerable number of observations widely scattered through the 
region have been put on record. (Fig. 5.) 
Such postglacial faults appear to have been first noticed by 
Mather * at Copake, N. Y., near the common corner of Massachu- 
setts and Connecticut. Similar faults have since been described by 
Matthew *° from St. John, New Brunswick; by Chalmers ** from 
many localities in the Province of Quebec; by C. H. Hitchcock ** 
from Littleton, N. H.; by Woodworth * from many localities in 
eastern New York and Massachusetts; by Lawson *? from Banning 
in western Ontario; by Hobbs from Sawyer, Wis.,*t and the 
French River in central Ontario;*? and by Loomis** from Mount 
Toby, Mass. While these faults are often small individually they 
are numerous and they grow large in the aggregate, and in some 
cases they are measured in tens of feet. 
The faults of eastern New York have been found chiefly along 
the lineament which follows the Hudson River and its continuation 
northward. The lineaments of the northeastern United States in 
their relation to the recorded earthquakes of the district as the data 
have been assembled by De Montessus have already been put upon 
record.** 
CONCLUSION 
The earthquake of February 28, 1925, was felt throughout the 
glaciated area of North America and at relatively few places outside. 
It was peculiarly an earthquake of this Laurentian area, and it is 
best explained as due to epeirogenic block movements as a result of 
* W. W. Mather, “ Geology of New York, report on first district,” 1843, pp. 156-157, 
3G. F. Matthew, “ Movements of the earth’s crust at St. John, New Brunswick, in 
postglacial times,’ Bull. Nat. Hist. Soe., New Brunswick, No. 12, 1894, pp. 3442. 
*7R. Chalmers, ‘Report on the surface geology and the auriferous deposits of south- 
eastern Quebec,” Geol. Surv. Can., Ann. Rept., vol. 10, 1897, pt. J, pp. 10-12. 
*8C. H. Hitchcock, “‘ The geology of Littleton,’ in History of Littleton, 1905, pp. 28-29. 
J. B. Woodworth, “ Postglacial faults of eastern New York,” Bull. 107, N. Y. State 
Museum, 1907, pp. 4-28. 
40 A. C. Lawson, “On some postglacial faults near Banning, Ontario,’ Bull. Seismol. 
Soc. Am., vol. 1, pp. 159-166. 
“= W. H. Hobbs, “‘ The late glacial and postglacial uplift of the Michigan Basin,” Mich. 
Geol. and Biol. Sury., Pub. 5, 1911, p. 45. 
#2 W. H. Hobbs, “ Postglacial faulting in the French River district of Ontario,’’ Am. 
Journ. Sci., vol. 1, 1921, pp. 507-509. 
#¥F. B. Loomis, ‘‘ Postglacial faulting about Mount Toby, Mass.,” Bul. Geol. Soc. 
Am., vol. 32, 1921, pp. 75-80. 
“ Beitriige zur Geophysik, vol. 8, 1907, pl. 2. 
