168 On the Pliocene Deposits of the Valley of the Thames. 



may have been formed by a gradual separation of calcareous 

 matter in suspension, by homogeneous attraction. If the ori- 

 ginal surface of the Wealden were irregular, or the uplifting of 

 the strata unequal, chalk, clays and sands might simultaneously 

 or alternately be exposed to the action of the waters, which would 

 produce the frequently repeated layers observed in the tertiary 

 strata. 



On the growing hills and rising valleys of the Pliocene period 

 a gigantic race of mammalia flourished, which in its turn was 

 swept away and entombed, just as we now find bones of the pre- 

 sent creation in beds of rivers and lakes : I have seen several bones 

 of Ox and Sheep inclosed in mud from the bed of the Thames, 

 which when hardened might be easily mistaken for those from 

 Ilford. For the support of so large a number of immense her- 

 bivora, a luxuriant vegetation must have existed ; without it the 

 Elephant and Irish Elk could not have thrived, or the Beaver 

 made a dwelling ; but indications of such are scarce, and I believe 

 have not been found at Ilford, with the single exception to which 

 I have alluded : this may be due to the larger trees having been 

 drifted away by the waters, or a condition of soil unfavourable 

 to their preservation. The presence of basins and fissures in the 

 upper layers of clay shows the interference of time, and marks out 

 an interesting series of events. After a long period of tranquil 

 deposition the strata had reached the surface, from the waters 

 having retired, or an elevation of the valley, and land succeeded 

 water ; streams and currents then hollowed out the surface into 

 basins and disappeared ; an exposure to the sun's rays followed, 

 by which the clays became hardened and fissures formed ; sub- 

 sequently the whole was again submerged and rapidly covered by 

 sand, which filled up the fissures and basins } and at last gravel 

 was washed over the whole, and it became the resting-place of 

 Man. The association of the remains of the Beaver, Megaceros 

 and Red Deer with those of Mammoth and Rhinoceros is inter- 

 esting, as it would show, that whatever the physical conditions 

 were under which these animals were destroyed, they could not 

 have been violent or universally destructive — that no grand con- 

 vulsion occurred by which all were alike overwhelmed ; but that 

 during a regular and uninterrupted course of events, certain ani- 

 mals became extinct from some combination of circumstances 

 unfavourable to their propagation, whilst others of different 

 habits and necessities remained for ages later, to be destroyed 

 only by the enterprise of Man ; — the bones of the first-mentioned 

 three are found in situations showing their existence down to a 

 very late period, and that a race of animals once the associates 

 of the Mammoth, Bear and Rhinoceros, have probably been the 

 contemporaries of our race. 



