150 GEOLOGY [CHAP. IX 



Letter 499 Roy shelf 1 keeping so long at exactly same level does cer- 

 tainly appear to me insuperable. 



What a wonderful fact this breakdown of old Niagara is. 

 How it disturbs the calculations about lengths of time before 

 the river would have reached the lakes. 



I hope Mrs. Lyell will read this to you, then I shall trust 

 for forgiveness for having scribbled so much. I should have 

 sent back Agassiz sooner, but my servant has been very 

 unwell. Emma is going on pretty well. 



My paper on South American boulders and " till," which 

 latter deposit is perfectly characterised in Tierra del Fuego, 

 is progressing rapidly. 2 



I much like the term post-Pliocene, and will use it in my 

 present paper several times. 



P.S. I should have thought that the most obvious objec- 

 tion to the marine-beach theory for Glen Roy would be the 

 limited extension of the shelves. Though certainly this is 

 not a valid one, after an intermediate one, only half a mile 

 in length, and nowhere else appearing, even in the valley 

 of Glen Roy itself, has been shown to exist. 



Letter 500 To C Lyell. 



1842. 



I had some talk with Murchison, who has been on a flying 

 visit into Wales, and he can see no traces of glaciers, but only 

 of the trickling of water and of the roots of the heath. It is 

 enough to make an extraneous man think Geology from 

 beginning to end a work of imagination, and not founded on 

 observation. Lonsdale, 3 I observe, pays Buckland 4 and myself 



1 For a description of the shelves or parallel roads in Glen Roy see 

 Darwin's " Observations on the Parallel Roads of Glen Roy, etc.," Phil. 

 Trans. R. Soc., 1839, p. 39 ; also pp. 171 et scq. of this volume. 



2 " On the Distribution of the Erratic Boulders and on the Contem- 

 poraneous Unstratified Deposits of South America," Trans. Geol. Soc., 

 Vol. VI., p. 415, 1842. 



3 William Lonsdale (1794-1871) obtained a commission in the 4th 

 Regiment at the age of sixteen, and served at Salamanca and Waterloo. 

 From 1829 to 1842 he held the office of Assistant-Secretary and Curator 

 of the Geological Society. Mr. Lonsdale contributed important papers 

 on the Devonian System, the Oolitic Rocks, and on palasontological 

 subjects. (Quart. Journ. Geol. Soc., Vol. XXVIII., p. xxxv., 1872.) 



4 William Buckland (1784- 1856) became a scholar of Corpus Christi 

 College, Oxford, in 1801 ; in 1808 he was elected Fellow and ordained 



