GEOLOGY [CHAP IX 



Letter 556 Ch. IV.- -The strangeness of the (Eocene) mammifers, 

 co-existing with recent shells. 



Ch. V. Curious pumiceous infusorial mudstone (p. 118) 

 of Patagonia; climate of old Tertiary period, p. 134. The 

 subject which has been most fertile in my mind is the 

 discussion from p. 135 to end of chapter on the accumulation 

 of fossiliferous deposits. 1 



Ch. VI. Perhaps some facts on metamorphism, but chiefly 

 on the layers in mica-slate, etc., being analogous to cleavage. 



Ch. VII. The grand up-and-down movements (and vertical 

 silicified trees) in the Cordillera : see summary, p. 204 and 

 p. 240. Origin of the Claystone porphyry formation, p. 170. 



Ch. VIII., p. 224. Mixture of Cretaceous and Oolitic 

 forms (p. 226) great subsidence. I think (p. 232) there is 

 some novelty in discussion on axes of eruption and injection, 

 (p. 247) Continuous volcanic action in the Cordillera. I think 

 the concluding summary (p. 237) would show what are the 

 most salient features in the book. 



Letter 557 To C. Lyell. 



Shrewsbury [August loth, 1846]. 



I was delighted to receive your letter, which was forwarded 

 here to me. I am very glad to hear about the new edition 

 of the Principles? and I most heartily hope you may live 

 to bring out half a dozen more editions. There would not 

 have been such books as D'Orbigny's S. American Geology 3 

 published, if there had been seven editions of the Principles 

 distributed in France. I am rather sorry about the small 

 type ; but the first edition, my old true love, which I never 

 deserted for the later editions, was also in small type. I much 



1 The last section of Chapter V. treats of " the Absence of extensive 

 modern Conchiferous Deposits in South America ; and on the contem- 

 poraneousness of the older Tertiary Deposits at distant points being 

 due to contemporaneous movements of subsidence." Darwin expresses 

 the view 'that " the earth's surface oscillates up and down ; and . . . 

 during the elevatory movements there is but a small chance of durable 

 fossiliferous deposits accumulating" (loc. at., p. 139). 



2 The seventh edition of the Principles of Geology was published in 



1847- 



3 Voyage dans PAmerique mcridionale execute, pendant les Annees 



5826-37. 6 vols,, Paris, 1835-43. 



