242 PEBBLES IN" CHALK. [Ch. XVII 



quartz and green schist, some of them 2 or 3 inches in diameter, has 

 justly excited much wonder. If these had been carried to the spots 

 where we now find them by waves or currents from the lands once 

 bordering the cretaceous sea, how happened it that no sand or mud 

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

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

 x. and 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 green- 

 stone, where every other particle of matter was calcareous ; and Mi*. Dar- 

 win 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, ob- 

 tained 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 Fistulana.\ 



The only other mode of transport which suggests 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 buoy- 

 ant 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, so common in Terra del Fuego, is said by Captain Cook to 

 attain the length of 360 feet, although the stem is not much thicker than 

 a man's thumb. 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 white 



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

 \ Mantell, Geol. of S. E. of England, p. 96. 



