185 



ultimate solid state at the same time, and under similar conditions, 

 and throw no difficulties whatever in the way of the igneous theory 

 of granite. Some writers, by confounding such joints with beds of 

 deposit (to which they bear no analogy), have been led into most pre- 

 posterous conclusions. 



Many of the great parallel veins of St. Austell Moor are described 

 as veins of segregation ; yet some of them are metalliferous. Most 

 of the metalliferous veins and cross courses of Cornwall are, however, 

 considered by the author as veins produced by mechanical disruption} 

 but on this hypothesis, the direction of such veins would (in part at 

 least) be affected by the structure and direction of the rock : and 

 from these considerations he thinks that we might (independently of 

 any direct observations) expect in some parts of the county a system 

 of veins running nearly magnetic east and west, and a great system 

 of cross-joints nearly at right angles to that direction. 



Before concluding the paper, he briefly notices the principal direc- 

 tions of the great cross courses and veins traversing the mountain 

 limestone of Derbyshire and Flintshire. The cross courses are nearly 

 in the direction of the beds, the veins nearly at right angles to them : 

 and these two directions harmonize very exactly with the theory which 

 refers both sets of fractures to a mere mechanical disruption of the 

 rock. 



April 8. — Edward Bellasis, Esq., Barrister at Law, New Square, 

 Lincoln's Inn ; and Henry English, Esq., of New Broad Street j were 

 elected Fellows of this Society. 



A paper was first read, entitled " Notice on the Junction of the 

 Portland and the Purbeck Strata on the Coast of Dorsetshire ;" by 

 William Henry Fitton, M.D., F.K.S., &c. 



The occurrence of silicified trunks of trees in the upright position, 

 with their roots in a thin bed of carbonaceous clay and coarse gravel, 

 a few feet above the top of the oolite, in the Lsle of Portland, was 

 mentioned some years ago by Mr. Webster*. Since that time Dr. 

 Buckland and Mr. De la Beche have inferred that both these trunks 

 and the Cycadeae described by the former f as occurring in the same 

 stratum, must actually have grown in the places where their remains 

 are found | ; and, more recently. Professor Henslow has ascertained 

 the existence of two other beds of clay, between that which includes 

 the trees and Cycadeae and the Portland stone. The author of the 

 present notice was so fortunate as to visit the island, during the last 

 summer, at a moment when the remains of Cycadeae were found in 

 one of these lotver beds, and to see some of them before they were 

 disturbed. The bed in which they occur is between those which are 

 called by the quarry-men " Cap" and " Skull-cap", both of which 

 consist of freshwater limestone ; the latter being separated from the 

 Portland stone by no more than two or three inches of clay. The 

 Cycadese in this lower bed were in some cases of very large horizontal 

 dimensions, and, like those in the dirt above the "Cap", were in 



* Geological Transactions, Second Series, vol. ii. p. 42. 



t Ibid. p. 395. X Geological Proceedings, vol. i. p. 219. 



