58 REPORT—1843. 
Report for 1842]. The authors first proceed to examine the phenomena attending 
earthquakes, commencing with the following propositions :—1. Earthquakes consist 
essentially of a wave-like motion of the whole solid ground; 2. the earthquake un- 
dulation is not simultaneous throughout the whole area agitated, but is progressive, 
and propagated with enormous velocity ; 3. the undulation is transmitted sometimes 
in the manner of an elongated, curved, or nearly straight belt, moving parallel to 
itself, and sometimes in the manner of a dilating elliptic or circular zone. The authors 
then describe earthquake phenomena as divisible into such as are of invariable occur- 
rence, and therefore characteristic, and such as are only occasionally witnessed. The 
characteristic phenomena consist, as announced by the Rev. John Mitchell of Cam- 
bridge, in the Phil. Trans. for 1760, of a peculiarly rapid wndulation, or wave-like 
motion of the ground, and a sharp vibratory jar, or ¢remor ; the undulation generally 
extending further from the source of the earthquake than the tremor. The occasional 
phenomena, observable only when the earthquake is violent, are a deep rumbling and 
grating noise, an alternate opening and closing of parallel fissures, and the escape of 
steam and sulphureous and other vapours, and hot water, from those fissures. In 
confirmation of these observations, the authors cite the earthquake of Conception, in 
1835, described by Captain Fitzroy, and that which visited the island of Hayti in 
May 1842. As examples of the second proposition, they mention the earthquake of 
Lisbon, and two others which have occurred during the present year. The first of 
these took place on the 4th of January, and was felt along the valley of the Missis- 
sippi, from the military posts on the frontier west of that river, to the coast of Georgia, 
and from 31° N. lat. to Iowa, a distance of about 800 miles in each direction; it 
occurred about 9 P.m., and was sufficiently violent to excite some alarm; throughout 
the region agitated the motion was both undulating and vibratory. From a compa- 
rison of the dates of the shock at twenty-seven different localities, it appears to have 
been simultaneous along a certain line, stretching ina 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 in- 
stant was linear, and that the earthquakes moved from W.N.W. to E.S.E. in the man- 
ner 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 Windward Islands, at Demerara, and Guiana, Bermuda, and most 
of the principal cities of the Atlantic seaboard of the United States, from Savannah to 
New York. Its range, in latitude, amounted to 35°, and in longitude to 23°: the 
longest diameter of this elliptical area extending from Demerara to New York, was 
about 2300 geographical miles; and its breadth, from Bermuda to Savannah, 770 
miles. The principal intensity of the disturbance was confined to a nearly north and 
south line, or belt, embracing St.Vincent’s, St. Lucia, Martinique, Dominica, Guada- 
loupe, 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 communication the authors propose a theory of the ori- 
gin and movement of earthquakes, as applied by them in explanation of the structure 
of the Appalachian Mountains. According to this theory, the wave-like motion of 
the earth’s surface during an earthquake is of the nature of an “actual billowy pul- 
sation in the molten matter,” upon which they suppose the crust of the earth floats, 
«©engendered by a linear or focal disruption and immediate collapse of the crust, 
accompanied by the explosive escape of highly elastic vapour.”’ The progressive waves 
of oscillation thus developed on each side of the axis of disturbance, would move off 
in parallel order, and form dilating elliptic zones. Supposing the earth’s crust to be 
ruptured only at a focal point, as in the orifice of a volcano, the receding pulsations 
would be approximately circular ; whereas, if the line of fracture were greatly elon- 
gated, and the pulsations observed but on one side, the advancing belt of waves would 
appear straight. 
The sea-waves caused by earthquakes are described as broad undulations of the water, 
moving in the same direction with the pulsation of the crust beneath, at the rate of 
