^2 Dr Johfi Davy on the 



rather than too low an estimate. And yet it is far below 

 the rate apparently established by the experiments with 

 corals cited in the preceding paragraph. We must admit 

 that the subject requires more accurate investigation. 



The stay of the expedition near any particular reef in the 

 Pacific was too short for any examinations by us. They 

 might easily be made by those residing in coral seas, either 

 in the manner adopted by Mr Allan, or more definitely 

 by placing marks upon particular species. By inserting 

 slender glass pins a certain distance from the summit of a 

 Madrepore, its growth might be accurately measured from 

 month to month. Two such pins in the surface of an As- 

 trsea would in the same manner, by the enlarging distance 

 between, shew the rate of increase in the circumference of 

 the hemisphere ; or, if four were placed so as to enclose an 

 area, and the number of polyps counted, the numerical in- 

 crease of polyps resulting from budding, might be ascertained. 

 It is to be hoped that some of the foreign residents at the 

 Sandwich, Society, Samoan, or Feejee Islands, will take this 

 subject in hand. There are also many parts of the West Indies 

 where these investigations might be conveniently made. 

 {To he continued.) 



On the Colour of the Bocks in the Lake District of the North 

 of England. By JoHN Davy, M.D., F.R.S., &c. Com- 

 municated by the Author. 



The careful observer in passing through the lake district 

 of Westmoreland and the adjoining counties, can hardly fail 

 of being struck by the prevailing dark hues of the rocks, often 

 in so great a degree as to be almost black, and of having his 

 curiosity excited as to the cause. 



If he break a portion, he will commonly find the very dark 

 hue to be superficial, or at least almost invariably of greater 

 intensity at the surface than in the interior ; and he will pro- 

 bably arrive at the conclusion, that this darker hue is a stain 

 or discolouration imparted by adhering adventitious matter. 

 This conclusion I believe to be the correct one. I shall 

 mention some circumstances which appear to confirm it. 

 Firstf Of the rocks of the district. These, for the most part. 



