Association of American Geologists and Naturalists. 341 
The following section furnished by the superintendent of the 
mines, shows the descending order and thickness of the several 
beds. 
1. Ferruginous clay mixed with rubble, - = - 30 feet. 
2. Red clay mixed with large masses of rock requir- 
ing blasting, = - - - - - =F TSO te 
3. Red clay similar to No. 1, in the seams of lead, ZOn ne 
4. Rock masses of limestone, - - - - A 
5. Lode, in red clay, of indifferent thickness, say 40 « 
2740 
Pursuing a general direction, at the bottom of the shaft, the 
ore is found to swell out laterally into pouches, or branches off 
so as to admit of lateral openings; so that the whole extent of 
the galleries is estimated at fifteen miles under ground. Over 
the surface, the lead region may be distinctly traced. 
Tuesday morning, May 2.—The secretary read a paper by 
Mr. Nicollet, on the earthquake of New Madrid. 
Prof. H. D. Rogers communicated to the Association the re- 
sults of his researches in relation to the recent earthquakes, and 
gave an outline of a theory of earthquake action, by which he 
and his brother Prof. W. B. Rogers propose to explain the forces 
concerned in the formation of anticlinal flexures, and to account 
for several other dynamic phenomena in geology. 
The characteristic features of earthquake motion, were shown to con- 
sist, as originally stated by Michell, ina peculiar rapid undulation or 
wave-like rocking of the ground, and a short vibratory jar or tremor, 
the tremulous shaking seldom extending to as great a distance from the 
source of the earthquake as the undulation. Details of several earth- 
quakes were quoted, to prove that the rocking motion is a true billowy 
undulation. Thus, during the severe shock so destructive at Hayti in 
May, 1842, the public square at Porto Plata was seen to undulate like 
the waves of the sea, the houses rocking to and fro like vessels in a 
storm. In the great earthquake which shook the Windward Islands on 
the 8th of February last, the earth in Antigua reeled to and fro for more 
than two minutes, and the same is mentioned in relation to the motion 
at Guadaloupe and every other locality, where the phenomena were 
carefully noted. 
The captain of the British steamer Tay reports, that being off Anti- 
gua and looking towards the shore, the hills appeared to be in motion. 
During the earthquake of Conception in 1835, the motion of the ground 
