350 Proceedings of the British Association for 1850. 



effects attempted to be attributed to them, were but insigni- 

 ficant ; and, indeed, nothing was more difficult in geology than 

 to attempt to connect present events with the past. 



Colonel Portlock supported the views of Professor Sedg- 

 wick ; while the statements of Sir C. Lyell were advanced by 

 others in favour of the erosive agency of rivers. 



Professor Hitchcock, in reply, disclaimed that the purport 

 of his statements went to establish the erosion of rivers as 

 tlie only cause of the formation of valleys. 



Dr Becker then read a paper " On the Constant Increase 

 of Elevation of the Beds of Rivers."" 



An interesting account of the discovery of " A Tertiary 

 Fossiliferous Deposit underlying Trap in the Island of Mull," 

 was communicated by the Duke of Argyll. — The island, 

 according to Professor Jameson, consists chiefly of trap, 

 granite, gneiss, and mica slate, all of which are seen in the 

 small bay near Ardtun, and at this place are some small layers 

 of brown coal interstratified with columnar trap. A little 

 north of the bay is Ardtun Head, a perpendicular cliff of 130 

 feet, intersected by a deep fissure or ravine, accessible from 

 the moor above. The cliff, the Duke remarked, consists 

 of the following horizontal beds : — 1. At the top, 20 or 30 feet 

 of rudely columnar trap ; 2. A thin laminated stratum con- 

 taining fossil leaves ; 3. Volcanic ashes ; 4. A second leaf- 

 bed ; 5. A second bed of volcanic ashes ; 6. A third leaf- 

 bed ; 7. Amorphous trap ; 8. Columnar trap, occupying the 

 base of the cliff. The volcanic ash-beds are undistinguish- 

 able from some modern formations at Vesuvius, and from the 

 tuff at Madeira and Auvergne. The second leaf-bed is 1^ to 2 

 feet thick, and in its lower part is a mere mass of vegetation. 

 In the third bed the leaves a^re less numerous, and imbedded 

 in a volcanic mud, which now forms a hard trap ; the 

 leaves are black and look charred, but this is not necessarily 

 the case : no trunks, boles, or even small twigs were found. 

 From these appearances the Duke concluded that the leaves 

 had accumulated from autumn to autumn in a shallow lake, 

 and had been overflowed by soft mud, in which they were pre- 

 served. The only indication of living animals found with 

 the leaves was the track of a worm. Chalk flints were found 



