Proceedings of the British Association. 245 



fissures, showing that the general conditions of the mass were such, 

 that after one system was formed, their nature was so modified by 

 time, that the same process might again take place from another 

 centre, without being materially disturbed by the former set of 

 fissures. If there had at any time been two contemporaneous centres 

 of mechanical force, such modification in their effects would have 

 been produced as to distinguish them from the effects of forces acting 

 consecutively in different periods of time. In concluding, Mr. 

 Hopkins remarked that the same phenomena were presented on a 

 small scale in the constitution of a volcanic mountain, which might 

 be expected on a much larger, wherever the earth's crust had under- 

 gone elevation. The theory that this crust rested on one uniform 

 fluid surface, was opposed by the fact of the shifting of the points of 

 eruption, a circumstance only explained by supposing a degree 

 of interruption in the connection of the internal fluid. — Prof. J. 

 D. Forbes described (at the request of Baron Waltershausen) an 

 instance of a fissure produced by pressure from below, seen in a sec- 

 tion of the Etnean mass. In this case the beds of lava appearing 

 horizontal, but in reality dipping towards the observer, were fissured 

 by a vertical dyke sending out horizontal branches between the layers 

 of lava, horizontal layers being sent off from a vertical dyke. In the 

 Val del Bove one dyke was seen standing out from a vertical cliff, in 

 which the upper surface preserved its original form, and bore the 

 trace of stream-marks. 



Saturday. 



* On the Coal Deposits of the Asturias/ by Mr. S. P. Pratt. — 

 Mr. Pratt gave a general account of a section taken from the neigh- 

 bourhood of Leon, in a north-west direction to the coast passing 

 through Oviedo. The strata rise from beneath tertiary deposits 

 which cover the plains of Leon and Castelli, at an angle of 30°, 

 which soon becomes nearly vertical, dipping north-by-west. They 

 consist of numerous alternations of grit and shale with thin beds of 

 limestone, and contain within about three miles of their rise a bed of 

 good coal, nearly nine feet thick. Between this point and the sum- 

 mit of the Pass, a distance of five leagues, several extensive faults 

 occur, by which the dip is more than once reversed, and several large 

 mountain masses of limestone appear, underlying the grits, &c. ; this 



