250 MISCELLANEA (continued'). [1881. 



you have said on Geology. I suppose that the classification 

 of the Silurian and Cambrian formations must be considered 

 the greatest or most important step ; for I well remember 

 when all these older rocks were called grau-wacke, and 

 nobody dreamed of classing them ; and now we have three 

 azoic formations pretty well made out beneath the Cambrian ! 

 But the most striking step has been the discovery of the 

 Glacial period : you are too young to remember the pro- 

 digious effect this produced about the year 1840 (?) on all our 

 minds. Elie de Beaumont never believed in it to the day 

 of his death ! The study of the glacial deposits led to the 

 study of the superficial drift, which was formerly never 

 .studied and called Diluvium, as I well remember. The study 

 under the microscope of rock-sections is another not incon- 

 siderable step. So again the making out of cleavage and the 

 foliation of the metamorphic rocks. But I will not run on, 

 having now eased my mind. Pray do not waste even one 

 minute in acknowledging my horrid scrawls. 



Ever yours, 

 CH. DARWIN. 



[The following extracts referring to the late Francis Mait- 

 land Balfour,* show my father's estimate of his work and 

 intellectual qualities, but they give merely an indication of 

 his strong appreciation of Balfour's most loveable personal 

 character : 



From a letter to Fritz Miiller, January 5, 1882 : 

 " Your appreciation of Balfour's book [' Comparative Em- 

 bryology '] has pleased me excessively, for though I could not 

 properly judge of it, yet it seemed to me one of the most 

 remarkable books which have been published for some con- 

 siderable time. He is quite a young man, and if he keeps 



* Professor of Animal Morpho- on the Aiguille Blanche, near 

 logy at Cambridge. He was born Courmayeur, in July, 1882. 

 1851, and was killed, with his guide, 



