of Tertiary Deposits. 113 



species of mollusca. It is not merely the extent of surface at 

 present occupied by these estuaries which has thus been de- 

 nuded of the crag ; but considerable tracts of marsh land for- 

 merly connected with them, but from which the water has since 

 been shut out, have also lost this original covering. Within a 

 very short distance of the Deben, another estuary, the Stour, 

 flows through a lacustrine deposit belonging to the newer plio- 

 cene or uppermost tertiary period ; and here, in addition to the 

 shells, is a considerable stratum of mammalian remains, which, 

 at one period, evidently extended as far as the opposite bank of 

 the river, a distance of about a mile and a half, or two miles. 



I must look forward some few thousand years, and anticipate 

 the time when, by the recession of the sea or the elevation of 

 the land, the deposits forming at the mouths of these estuaries 

 has become accessible, and is made the subject of geological in- 

 vestigation. I must also assume, that the geologists of that re- 

 mote period have followed the same course of induction that has 

 recently been pursued, and have arrived at similar conclusions 

 respecting the course to be adopted in ascertaining the relative 

 antiquity of tertiary deposits. The age of the formation in 

 question, then, is about to be tested by comparing its organic 

 remains with the then existing species. Of what will these fos- 

 sils consist, and whence will they originally have been derived ? 

 The bones of such animals as are now drifted down the rivers 

 Deben and Stour will be mingled with those of the extinct mam- 

 malia of the uppermost or newer pliocene period. The living spe- 

 cies of mollusca now inhabiting the German Ocean, will be found 

 associated with the extinct testacea of the newer pliocene, older 

 pliocene, and perhaps even with the miocene or middle epoch. Yet 

 this deposit, in which the organized beings of different geological 

 periods shall be found thus indiscriminately mingled, will be one 

 exhibiting every appearance of regular stratification, a deposit ill 

 which a large portion of testacea will be found naturally 

 grouped, and in which there will be the clearest evidence of 

 their having become entombed on the spot which they had long 

 previously inhabited. That the influences of causes now in 

 operation is really producing such an effect as the one now de- 

 scribed, admits of almost actual demonstration ; for the fossil 

 shells of the crag are thrown up along various parts of the Suf- 



YOL, XXII. XO. XL1U. JANUASIY 1807. H 



