BRITISH ASSOCIATION. 
217 
tary posts on the frontier west of tliat river, to the coast of 
Georgia, and from 31° N. lat. to Lowa, a distance of about 800 
miles in each direction ; it occurred about 9 p.m., and was suffi- 
ciently voilent to excite some alarm ; throughout the region 
agitated the motion was both undulating and vibratory. From 
a comparison of the dates of the shock at twenty-seven different 
localities, it appears to have been simultaneous along a certain 
line stretching in a N.N.E. direction from the western margin of 
Alabama to Cincinnati, a length of more than 500 miles ; it 
was also synchronous along other lines parallel to this ; places 
to the westward experienced the shock earlier than the other 
localities, the intervals being in proportion to the distance. 
From these facts the authors infer that the area agitated at a 
given instance was linear ^ and that the earthquakes moved from N. 
N.E. to E.S.E. in the manner of an advancing wave. The velocity 
with which the shock was propagated appears to have exceeded 
thirty miles per minute. The second, or Guadaloupe earthquake 
was felt along the Winwood Island, at Demerara, Guianaj 
Bermuda, and most of the principal cities of the Atlantic sea. 
board of the United States, from Savannah to New York. Its 
range, in latitude, amounting to 35°, and in longitude to 23°, 
the longest diameter of this elliptical area extending from Deme- 
rara to New York, was about 2,300 geographical miles ; and 
its breadth, from Bermuda to Savannah, 700 miles. The princi- 
pal intensity of the disturbance was confined to a nearly N. and 
S. line, or belt, or embracing St. Vincent^ s, St. Lucia, Martini- 
que, Dominica, Guadaloupe, and Antigua ; and thence prolonged 
to the continent of South America, and to Bermuda. Along 
this curved axis the shock was simultaneous : and from a com- 
parison of observations made at other stations, it appears to have 
been propagated eastward and westward at the rate of twenty- 
seven miles per minute. In the second part of their communi- 
cation the authors propose a theory of the origin and movement of 
earthquakes, as applied by them in explanation of the structure 
VOL. II NO. XVIII Z 
