204 



was once overflowed by the Trappean matter, and that it was the 

 intense and continued heat of this great incumbent mass of igneous 

 material^ which produced the extensive and remarkable altera- 

 tions over large spaces where no dykes are to be seen. 



Prof. Rogers then referred to what he considered a yet more 

 curious effect of the Trap on the adjoining rocks, which, although 

 observable at other localities, he had not elsewhere seen so 

 clearly exhibited. While, as before remarked, no decided tilting 

 of the strata was noticed in the immediate vicinity of the dykes, 

 he observed that a structural condition had been induced in the 

 horizontal beds, which might easily lead an unpractised observer 

 to suppose that this had been forced into almost vertical dips. 

 These rocks, where in contact with the Trap, are traversed by 

 vertical joints, or cleavage planes, so close to one another as to 

 divide the mass into a system of narrow prisms or plates parallel 

 to the walls of the dyke. These planes of division, caused no 

 doubt by the Trap, are distinctly perceptible at the distance of 

 twenty or more feet on either side of even a narrow dyke, and 

 are so decided within a few feet, as almost completely to mask 

 the original planes of stratification. They thus present the ap- 

 pearance of very deeply dipping beds on each side of the dyke, 

 as if suddenly bent upwards by the ascending eruptive mass. 



Dr. Charles T. Jackson read the following extracts from 

 a letter of M. Elie de Beaumont, dated Paris, March 23d, 

 1855: — 



" I have seen, with much pleasure, in the Daily Evening Trav- 

 eller, that the Boston Society of Natural History has given its 

 attention to the results of the researches of M. Alexis Perrey on 

 Earthquakes, and to the brief report which I made to the Acad- 

 emy on the subject. If I had found opportunity, I should have 

 sent you the report. You have yourself presented, on this sub- 

 ject, considerations which appear to merit the attention of trav- 

 ellers, who have occasion to observe volcanoes where the lava 

 flows freely in a continuous manner. Travellers might also 

 compare the days of eruptions, with those of the moon's phases, 

 according to the method employed by M. Perrey in earth- 

 quakes. 



