324 PEBBLES IN CHALK. [Ch. XVII 



were transported thither at the same time ? We cannot conceive such 

 rounded stones to have been drifted like erratic blocks by ice (see 

 Chaps. X., XI.), for that would imply a cold climate in the Cretaceous 

 period — a supposition inconsistent with the luxuriant growth of large 

 chambered univalves, numerous corals, and many fish, and other fossils 

 of tropical forms. 



Now in Keeling Island, one of those detached masses of coral which 

 rise up in the wide Pacific, Captain Ross found a single fragment of 

 greenstone, where every other particle of matter was calcareous ; and 

 Mr. Darwin concludes that it must have come there entangled in the 

 roots of a large tree. He reminds us that Chamisso, the distinguished 

 naturalist who accompanied Kotzebue, affirms that the inhabitants of 

 the Radack archipelago, a group of lagoon islands in the midst of the 

 Pacific, obtained stones for sharpening their instruments by searching 

 the roots of trees which are cast up on the beach.* 



It may perhaps be objected, that a similar mode of transport 

 cannot have happened in the cretaceous sea, because fossil wood is 

 very rare in the chalk. Nevertheless wood is sometimes met with, 

 and in the same parts of the chalk where the pebbles are found, both 

 in soft stone and in a silicified state in flints. In these cases it has 

 often every appearance of having been floated from a distance, being 

 usually perforated by boring-shells, such as the Teredo and Fistu- 

 lana.\ 



The only other mode of transport which suggested itself is sea- 

 weed. Dr. Beck informs me that in the Lym-Fiord, in Jutland, the 

 Fucus vesiculosus, often called kelp, sometimes grows to the height 

 of 10 feet, and the branches rising from a single root form a cluster 

 several feet in diameter. When the bladders are distended, the plant 

 becomes so buoyant as to float up loose stones several inches in 

 diameter, and these are often thrown by the waves high up on the 

 beach. The Fucus giganteus of Solander (Macrocystes pyrifera, 

 Hooker), so common in Terra del Fuego, was descried by Captain 

 Cook as attaining the length of 360 feet, although the stem is not 

 much thicker than a man's thumb. Dr. Hooker found the same sea- 

 weed 700 feet long. J It is often met with floating at sea, with shells 

 attached, several hundred miles from the spots where it grew. Some 

 of these plants, says Mr. Darwin, were found adhering to large loose 

 stones in the inland channels of Terra del Fuego, during the voyage 

 of the "Beagle" in 1834 ; and that so firmly, that the stones were 

 drawn up from the bottom into the boat, although so heavy that they 

 could scarcely be lifted in by one person. Some fossil sea-weeds have 

 been found in the Cretaceous formation, but none, as yet, of large size. 



But we must not imagine that because pebbles are so rare in the 



* Darwin, p. 549. Kotzebue's First Voyage, vol. iii. p. 155. 

 f Mantel!, GeoL of S.E. of England, p. 96. 

 % Flora Antarctica, vol. ii. p. 464. 



