186 LYELL'S ELEMENTS OF GEOLOGY. 



Origin of White Chalk. 



With these fossils the remains of fish and Crustacea are not 

 uncommon ; but we meet with no bones of land animals, nor 

 any terrestrial or fluviatile shells, nor any plants, except pieces 

 of drift-wood and sea-weed, nor any sand or pebbles ; all the 

 appearances concur in leading us to believe that this deposit was 

 formed in a deep sea, far from land, and at a time when the 

 European fauna was perfectly distinct from that of the tertiary 

 period, from which its numerous species of plants and animals 

 entirely differ. 



Origin of the White Chalk. — Having then come to the con- 

 clusion, that the chalk was formed in an open sea of some depth, 

 we may next inquire, in what manner so large a quantity of this 

 peculiar white substance could have accumulated over an area 

 many hundred miles in diameter, and some of the extreme 

 points of which are distant, as we shall see in the sequel, more 

 than 1000 geographical miles from each other. 



It was remarked in an early part of this volume, that some 

 even of that chalk which appears to an ordinary observer quite 

 destitute of organic remains, is nevertheless seen under the 

 microscope to be full of fragments of corals and sponges ; the 

 valves of Cytherina, the shells of foraminifera, and still more 

 minute infusoria. (See p. 41.) 



Now it had been often suspected before these discoveries, that 

 white chalk might be of animal origin, even where every trace 

 of organic structure has vanished. This bold idea was partly 

 founded on the fact, that the chalk consisted of pure carbonate 

 of lime, such as would result from the decomposition of testacea, 

 echini, and corals, and in the passage observable between these 

 fossils when half decomposed into chalk. But this conjecture 

 seemed to many naturalists quite vague and visionary, until its 

 probability was strengthened by new evidence brought to light 

 by modern geologists. 



We learn from Lieutenant Nelson, that, in the Bermuda 

 islands, there are several basins or lagoons almost surrounded 

 and inclosed by reefs of coral. At the bottom of these lagoons 

 a soft white calcareous mud is formed by the decomposition of 

 Eschara, Flustra, Cellepora, and other soft corallines. This 

 mud, when dried, is undistinguishable from common white earthy 

 chalk ; and some portions of it, presented to the Museum of the 

 Geological Society of London, might, after full examination, be 

 mistaken for ancient chalk, but for the labels attached to them. 

 About the same time Mr. C. Darwin observed similar facts in the 

 coral islands of the Pacific; and came also to the opinion, that 

 much of the soft white mud found at the bottom of the sea near 

 coral reefs has pas'sed through the bodies of worms, by which 



