1878.] GEOLOGY. 411 



In the spring he received a copy of Dr. E. von Mojsisovics' 

 ' Dolomit Riffe,' his letter to the author (June i, 1878) is 

 interesting as bearing on the influence of his own work on 

 the methods of geology. 



" I have at last found time to read the first chapter of your 

 ' Dolomit Riffe,' and have been exceedingly interested by it. 

 What a wonderful change in thj future of Geological chro- 

 nology you indicate, by assuming the descent theory to be 

 established, and then taking the graduated changes of the 

 same group of organisms as the true standard ! I never 

 hoped to live to see such a step even proposed by any one." 



Another geological research which roused my father's 

 admiration was Mr. D. Mackintosh's work on erratic blocks. 

 Apart from its intrinsic merit the work keenly excited his 

 sympathy from the conditions under which it was executed, 

 Mr. Mackintosh being compelled to give nearly his whole 

 time to tuition. The following passage is from a letter to 

 Mr. Mackintosh of October 9, 1879, and refers to his paper 

 in the Journal of the Geological Society, 1878 : — 



" I hope that you will allow me to have the pleasure of 

 thanking you for the very great pleasure which I have derived 

 from just reading your paper on erratic blocks. The map 

 is wonderful, and what labour each of those lines show ! I 

 have thought for some years that the agency of floating ice, 

 which nearly half a century ago was overrated, has of late 

 been underrated. You are the sole man who has ever noticed 

 the distinction suggested by me * between flat or planed 

 scored rocks, and mammillated scored rocks."] 



C. Darwiii to C. Ridley. 



Down, November 28, 1878. 



Dear Sir, — I just skimmed through Dr. Pusey's sermon, 

 as published in the Guardiaii^ but it did [not] seem to me 



* In his paper on the * Ancient Glaciers of Carnarvonshire,' Phil. Mag. 

 xxi. 1842. See p. 187. 



