PRINCIPLES AND METHODS OF PALAEONTOLOGY. 381 



tions enumerated above; but it occasionally happens that accidental 

 floods sweep them away into low grounds, hollows, or caves, where they 

 rest and become covered up with the hue mud deposited as the waters 

 subside; or livini^ animals may be swallowed uj) in peat-mosses and in 

 swamps; or their remains may be exposed to the action of springs 

 highly charged with calcareous matter, and thus become coated with 

 earhonate ot lime; or the wind may envelop them ia drift sand ; and iu 

 all these instances they will be more or less effectually protected from 

 further chnnge. 



The imbedding and preservation of the exuvia of those marine ani- 

 mals and plants which are not destroyed by the carnivorous and herb- 

 ivorous races, on the other hand, is hardly a matter of chance, but must 

 always inevitably take jdace. The sea is incessantly wearing away the 

 shores against which it beats, and the shallow grounds over which its 

 currents and tides race, undermining and cutting them away, and grind- 

 ing the fragments down by their mutual friction into boulders, shingles, 

 pebbles, sand, and mud. It then carries away the finer nmterials, and 

 spreads them over the deeper and quieter portions of its bed, whei-e 

 they are arranged in successive layers, which gradually rise into banks 

 of mud and sand. Brooks and streams, constantly bringing down sim- 

 ilar materials from the higher grounds inland, add to these deposits, or 

 form similar ones peculiar to themselves, thus giving rise to the " deltas" 

 and the " bars" found at the mouths of most rivers. In all the 

 quieter and not too deep parts of the sea bed, therefore, it is as if a con- 

 stant though very slow rain of fine earthly particles were going on, and 

 consequently every dead shell, every undestroyed bone, which is left on 

 the bottom, is sooner or later covered up and i)rotected from further 

 destruction. Just as the showers of fine ashes which fell from Vesuvius 

 seventeen centuries ago so covered up and protected the remains of 

 Herculaneum and Pompeii, that even now the smallest relics of lloman 

 daily life are preserved for our inspection, so may the muddy deposit 

 now taking place over a large extent of the j) resent sea bottom preserve, 

 for the inspection of future generations, the remains of the creatures at 

 present living and dying there. 



For the sake of clearness it has been provisionally assumed that, iu 

 all these instances, the organic bodies have been preserved by being 

 enveloped in masses of inorganic matter ; that the mud which forms the 

 bottom of seas and rivers is, in all cases, pulverized ro(!k brought from 

 other localities. It is very rare, however, to find mud purely of this 

 character, and there are some remarkable accumulations at present 

 taking place, of which ev^ery particle is derived from organisms which 

 have once lived, the apparent mud, in which the large organisms are 

 imbedded, being nothing but a mass of shells of minuter forms inter- 

 mingled with fragments of larger ones. 



5. JMost important consequences How from a recognition of the fact 

 that the modes of jjreservation of the renmins of animals and plants 

 last described far outweigh every other iu importance and extent. This 

 may be made more clear by again using the instance of Ponq)eii and 

 Hercuhmeum as an illusti'ation. Suppose that long after these cities 

 were buried others had been built over them by some of the many bar- 

 bariaii iuvaders of Italy, during tlie decline of the empire, and that 

 after a while Vesuvius had entombed these under another shower of 

 ashes; and that these had, after a few hun<lred years of existence, un- 

 dergone a like fate, so that the Avhole of this part of Italy was buried' 

 under volcanic accumulations, on the surface of which flourished the 

 villages and vineyards of a race ignorant of the existence of a previous 



