346 Association of American Geologists and Naturalists. 
Should the line of disruption, on the other hand, be greatly elongated, 
and the pulsations on one side of it only be studied, the belt of advane- 
ing waves may seem straight, the apparent form of the lines of syn- 
chronous shock in the recent Mississippi earthquake. 
The views here suggested of the nature and cause of the wave-like 
motion in earthquakes, rest upon a generalization which the authors of 
this communication regard as one of the soundest deductions in geolo- 
gy, that fluid lava underlies large regions of the earth’s crust, and that 
this crust is of very moderate thickness. If it be conceded that the earth- 
quake undulation and its attendant phenomena imply actual pulsation in 
a subjacent fluid, the whole tendency of geological fact is to demon- 
strate that this fluid can be only intensely heated rock or lava. And 
conversely, the frequent recurrence of earthquakes in every known dis- 
trict of the globe, and the vast distances over which these pulsations 
are transmitted,—in some instances more than three thousand miles,— 
are facts which lend strong support to the doctrine of central heat, 
since they indicate that the internal igneous fluid is absolutely universal. 
Prof. Rogers next gave a concise description of the structural features 
of the great Appalachian chain of the United States, illustrating the 
nature of the flexures in the strata, their remarkable parallelism and 
great length, their distribution in groups, and the law of their succes- 
sively diminishing curvation, crossing the region from southeast to north- 
west. Referring to the published volume of the Transactions of the 
Association, for a full exposition of the views of his brother and him- 
self in explanation of the phenomena, he confined himself to shewing 
that the bending and elevation of strata in regular flexures or axes, is 
the necessary consequence of a wave-like oscillation of the crust, act- 
ing simultaneously with a horizontal or tangential pressure. The iden- 
tity of the ancient undulations, thus causing permanent flexures, with 
modern earthquakes, was then maintained, and facts appealed to in 
proof that these convulsions sometimes produce permanent anticlinal 
arches of gentle curvature, at the present day. 
Other applications of the theory of the paroxysmal undulation of the 
earth’s crust, were then adverted to; particularly the ready explanation 
it affords of the remarkably wide and uniform distribution of the coarse 
materials in some of our rocks of mechanical origin. It was argued, 
that to no aqueous action less extensive than that of an inundation as broad 
and diffused as an earthquake, can we attribute the strewing of the 
great sheets of matter now forming certain conglomerates and sand- 
stones. Repeated oscillations of the crust, if very vehement, and ac- 
companied as they would be by some permanent elevation of the sur- 
face, might send the ocean upon the dry land, and form of the frag- 
mentary detritus a superficial layer as broad as the area inundated. 
