202 Proceedings of' the Royal Socieiy. 



shale within its mass, and penetrated laterally among the beds to 

 the extent of one hundred feet or more on the east side. On the 

 south flank of the highest part of the crag we have a section exhi- 

 biting the relations of the two rocks. The trap has the fitrm of an 

 arch, of perhaps twenty feet radius, with a long straight tabular 

 mass about three feet farther to the east. A mass of shale lies un- 

 der the arch exhibiting a laminar structure ; in the portions conti- 

 guous to the trap, its substance is hardened, and the planes of the 

 lamina, instead of being straight and parallel, are arranged concen- 

 trically with the curved surface of the trap which covers them. 

 Portions of shale also lie under and above the thin tabular project- 

 ing mass of trap, and these likewise conform themselves to its sur- 

 face. The inference is, that, independently of the original slaty 

 form of the shale, a secondary laminar structure was induced upon 

 it, by the heat of the fused trap being propagated through it pro- 

 gressively and unequally, each portion as it was dried and harden- 

 ed, separating from that beyond it. 3. The crag exhibits a striking 

 example of the effects of denudation. The north end of the ridge, 

 which is low, and on a level with the surface of the land westward, 

 has merely had its covering of shale stripped oflf, and exhibits a few 

 trifling indentations ; but the south end, which rises in bold relief 

 above the adjacent land, has been cut into seven distinct hillocks, 

 separated by transverse ravines, which are steep in the sides, and 

 from ten to sixty feet in depth. The appearance of these ravines 

 shews, that they must have been cut by powerful currents flowing 

 from the west. 



ii. Notice of Experimental Researches into the Laws of cer- 

 tain Hydroclynamical Phenomena that have not hitherto 

 been reduced into Conformity with known Laws. By 

 John Scott Russell, Esq. Lecturer on Natural Philoso- 

 phy. 

 April 17. — Sir Henry Jakdine in the Chair. The follow- 

 ing communications were read : 



]. On the Constitution of the Earth's Atmosphere in Remote 

 Geological Epochs. By Professor Johnston, Durham. 

 This is the first paper of a promised series on the subject here 

 announced. In the present paper the author endeavours to shew, 

 that in remote epochs the atmosphere was more extensive and heav- 

 ier than it is now, that it contained a greater absolute quantity of 

 oxygen, and that this quantity has gradually diminished up to our 



