1 62 King George s Sound. paet l 



plish colours ; both varieties being generally, but not 

 always, mixed with small particles of quartz, and being 

 cemented into a more or less perfect stone. The rounded 

 calcareous grains, when heated in a slight degree, in- 

 stantly lose their colours ; in this and in every other 

 respect, closely resembling those minute, equal-sized 

 particles of shells and corals, which at St. Helena have 

 been drifted up the sides of the mountains, and have 

 thus been winnowed of all coarser fragments. I cannot 

 doubt, that the coloured calcareous particles here have 

 had a similar origin. The impalpable powder has 

 probably been derived from the decay of the rounded 

 particles ; this certainly is possible, for on the coast of 

 Peru, I have traced large unbroken shells gradually 

 falling into a substance as fine as powdered chalk. 

 Both of the above-mentioned varieties of calcareous 

 sandstone frequently alternate with, and blend into, 

 thin layers of a hard substalagmitic 1 rock, which, even 



1 I adopt this term from Lieut. Xelson's excellent paper on trie 

 Bermuda Islands (' Geolog. Trans.' vol. v. p. 106), for the hard, com- 

 pact, cream- or brown-coloured stone, 'without any crystalline struc- 

 ture, which so often accompanies superficial calcareous accumulations. 

 I have observed such superficial beds, coated with substalagmitic 

 reck, at the Cape of Good Hope, in several parts of Chile, and over 

 wide spaces in La Plata and Patagonia. Some of these beds have 

 been formed from decayed shells, but the origin of the greater 

 number is sufficiently obscure. The causes which determine water 

 to dissolve lime, and then soon to redeposit it. are not, I think, known. 

 The surface of the substalagmitic layers appears always to be 

 corroded by the rain-water. As all the above-mentioned countries 

 have a long dry season, compared with the rainy one, I should have 

 thought that the presence of the substalagmite was connected with 

 the climate, had not Lieut. Nelson found this substance forming 

 under sea-water. Disintegrated shell seems to be extremely soluble ; 

 of which I found good evidence, in a curious rock at Coquimbo in 

 Chile, which consised of small, pellucid, empty husks, cemented 

 together. A series of specimens clearly showed that these husks 

 had originally contained small rounded particles of shells, which had 

 been enveloped and cemented together by calcareous matter (as 

 often happens on sea-beaches), and which subsequently had decayed, 

 and been dissolved by water, that must have penetrated through the 

 calcareous husks, without corroding them, — of which processes, every 

 stage could be seen. 



