PART II. CHAPTER XV. 



187 



Pebbles in Chalk, whence derived. 



the stony masses of coral are everywhere bored ; and other por- 

 tions through the intestines of fish ; for certain gregarious fish 

 of the genus Sparus are visible through the clear water, brows- 

 ing quietly, in great numbers, on living cor- 

 Fig. 162. Fig. 163. als, like grazing herds of graminivorous 

 quadrupeds. On opening their bodies, Mr. 

 Darwin found their intestines filled with 

 impure chalk. This circumstance is the 

 more in point, when we recollect how the 

 fossilist was formerly puzzled by meeting 

 with certain bodies, called cones of the 

 larch, in chalk, which were afterwards 

 Coproiites offish called lulo- Yecoguized by Dr. Buckland to be the ex- 

 cido-copri, from the chalk, ^remcnt of fish.* Thcsc Spiral coproiites 

 (see Figures) like the scales and bones of fossil fish in the chalk, 

 are composed chiefly of phosphate of lime. 



Single pebbles in chalk. — The general absence of sand 

 and pebbles in the white chalk has been already mentioned ; 

 but the occurrence here and there of a few isolated pebbles 

 of quartz and green-schist, some of them two or three inches 

 in diameter, in the south-east of England, 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 were transported thither at the same time ? We cannot 

 conceive such rounded stones to have been drifted like erratic 

 blocks by ice, for that would imply a cold climate in the cre- 

 taceous period ; a supposition inconsistent with the luxuriant 

 growth of large chambered univalves, numerous corals, and 

 many fish, and other fossils of tropical forms. (See p. 86.) 



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 Mr. Darwin concludes that it must have 

 come there entangled in the roots of a large tree. He reminds 

 us that Chamisso, a 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 sharpenii^ their instruments by searching the roots 

 of trees which are cast up on the beach.f 



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

 cannot have happened in the cretaceous sea, because fossil wood 



* Geol. Trans. Second Series, vol. iii. p. 232. plate 31. figs. 3. and 11. 

 t Darwin, p. 549. Kotzebue's First Voyage, vol. iii. p. 155. 



