170 THE SEA. 



lies an ocean-floor of soft cretaceous clay, the produce 

 of some coral reef, which has been browsed upon and 

 ground to powder by the molar teeth of myriads of 

 Parrot-fishes (Scaridce and Labridce) for ages. From 

 the full-fed whales faecal pellets are constantly drop- 

 ping, each of which consists of siliceous matter, resolv- 

 able, indeed, into frustules of Diatoms, and shells of 

 Polycysts, and spicules of Sponges, but now concreted 

 into an irregularly nodulous, compact mass. These fall 

 on the soft, calcareous, pasty bed below, and sink into 

 its impalpable bosom ; the white, creamy semifluid 

 closing over each nodule, and burying it from all dis- 

 turbance. Geologic periods pass ; upheavings of the 

 crust roll away the sea into other channels, and the 

 calcareous bed is a thick stratum of chalk, the white 

 cliffs of the Albion of the day. The pickaxe and the 

 spade go to work, and lo ! irregular nodules of flint 

 appear, and savans wonder how they came there. The 

 hammer breaks them open, and the lapidary, with his 

 lathe, grinds out a thin section, which the microsco- 

 pist puts under his best powers. He finds that spicules 

 of Sponges, and valves and fragments of Diatomacece 

 are abundant, mingled with a host of amorphous par- 

 ticles too greatly comminuted to be referred to any 

 determinate form. Enough is seen, however, to show 

 the organic origin of the flint-masses ; and as to the 

 question of their introduction into the chalk, that no 

 longer remains a mystery. 



Among the organisms found in the cretaceous flint 

 nodules, none have elicited more discussion than cer- 



