Correspondence. 519 



perished. The rings showed a slow but uniform growth of about 

 twelve annual lines to an inch. Trees of this size far exceed those 

 now growing south of Loch Maree in less exposed positions. The 

 roots are extremely singular. In one case Mr. Brown found a 

 plexus of inosculating roots, ten feet in diameter, forming almost a 

 platform, the separate roots measuring ten inches in width. 



Mr. Brown proceeds to infer that the change of climate must have 

 been very considerable to have first caused the growth of such fine 

 forest trees, and then their overthrow and the production of peat. 



Mr. Brown suggests that this Higliland region of Laurentian 

 Gneiss surmounted by Cambrian rocks has remained elevated above 

 the sea, and clothed with vegetation when all the younger rocks 

 were submerged beneath its waters, which would by their genial 

 iufluence favour a more rich vegetation than the present climate. 



5. Mr. E. B. Kemp-Welch, of Lindfield, Malvern (Sept. 17th) an- 

 nounces the discovery of a Trilobite new to the Malvern district, 

 viz : Ampyx nudus, March ; the specimen was obtained " from the 

 Woolhope limestone, at the tunnel shaft, on the Worcester and 

 Hereford Eailway, Oolwall, near Malvern." Mr. Welch encloses a 

 sketch, which is certainly very like an Ampyx, a remarkable find, 

 indeed, in the Upper Silurian of Malvern. — We had, however, the 

 pleasure to see this new find the other dsij ; it was kindly brought 

 for our inspection by Dr. Grindrod, of Malvern. We are sorry to 

 state that it is manufactured. — Edit. 



MACKINTOSH ON WELSH VALLEYS. GEIKIE ON SCOTTISH KAMES. 

 To the Editor of the Geological Magazine. 



Sir, — As sure as there are alternations of hard and soft strata in 

 the course of a valley or river so sure will there be alternations of 

 gorge and alluAdal flat. Mr. Mackintosh credits this principle to 

 Professor Jukes. I, however, first published it in 1857, in the first 

 edition of "Eain and Eivers," p. 53, in accounting for the river- 

 gorges through the north and south Downs. Also at page 174. And I 

 have since sung the cuckoo-note in various letters to periodicals. In 

 the " AthenEeum " of 26th December, 1863, 1 advanced the principle 

 as " the open sesame of the secret of the parallel terraces of Glen Eoy." 

 In February, 1864, Mr. Jukes kindly sent me a copy of an article of 

 his in the " Eeader." I remarked to him that he had used my 

 argument. His letter in reply begins, " I had your description of 

 Glen Eoy in my head when I wrote the passage you allude to." In 

 page 16, second edition of "Eain and Eivers," I have said, "Any 

 one may make parallel terraces for himself in the road-side gutter. 

 Dam up the run of rain. A pool will form above the dam. Every 

 rain will deposit on the bed of the pool, till the flat alluvium rises 

 to the height of the dam. Take away the dam. The rain cuts 

 through the alluvium which it has deposited and runs between two 

 parallel terraces till they vanish by denudation. This is the whole 

 secret of the terraces of Glen Eoy, or of any other valley or river." 



