uncovered. Mr. J. Geikie maintains, in his last very interesting work
( Prehistoric Europe, 1881), that the more perfect scratches are
probably due to the last access of cold and increase of ice, during the
long-continued, intermittent glacial period.
{224b} Many geologists have felt much surprise at the complete
disappearance of flints over wide and nearly level areas, from which the
chalk has been removed by subaerial denudation. But the surface of every
flint is coated by an opaque modified layer, which will just yield to a
steel point, whilst the freshly fractured, translucent surface will not
thus yield. The removal by atmospheric agencies of the outer modified
surfaces of freely exposed flints, though no doubt excessively slow,
together with the modification travelling inwards, will, as may be
suspected, ultimately lead to their complete disintegration,
notwithstanding that they appear to be so extremely durable.
{225a} Archives de Zoolog. exper. tom. iii. 1874, p. 409.
{225b} Nouvelles Archives du Museum, tom. viii. 1872, pp. 95, 131.
{226} Morren, in speaking of the earth in the alimentary canals of
worms, says, pr sepe cum lapillis commixtam vidi: De Lumbrici
terrestris Hist. Nat. &c., 1829, p. 16.
{227} Perrier, Archives de Zoolog. exper. tom. iii. 1874, p. 419.
{228a} Morren, De Lumbrici terrestris Hist. Nat. &c., p. 16.
{228b} Archives de Zoolog. exper. tom. iii. 1874, p. 418.
{234} This conclusion reminds me of the vast amount of extremely fine
chalky mud which is found within the lagoons of many atolls, where the
sea is tranquil and waves cannot triturate the blocks of coral. This mud
must, as I believe ( The Structure and Distribution of Coral-Reefs, 2nd
edit. 1874, p. 19), be attributed to the innumerable annelids and other
animals which burrow into the dead coral, and to the fishes,
Holothurians, &c., which browse on the living corals.
{236} Anniversary Address: The Quarterly Journal of the Geological
Soc. May 1880, p. 59.
142