186 7. J DAWKINS LOWEK BRICK-EARTHS. 93 



clay (j^o. 5), Brick-earth, and gravel, irregularly stratified, with the 

 layers highly contorted, and of such an irregular confused character 

 that no recognized geological term will accurately express its nature. 

 It is termed Loess* by Mr. Prestwich, and is the exact equivalent of 

 the '' Trail " described by the Eev. 0. Pislier in the summer of 

 1866t. It contains pebbles of quartz, sandstone of probably Car- 

 boniferous as well as of Eocene age, chalk, and Lydian stone, with 

 angular and waterworn flints. Large tabular flints and masses of 

 greywethers (one of which weighed at least 26 pounds) occur in 

 the lower part. There are also irregular layers of peroxide of 

 manganese and of a ferruginous conglomerate. There is one point 

 deserving attention in this bed : the long axes of the pebbles are 

 in the main vertical, instead of occupying the horizontal position of 

 those which have been deposited by water. The surface-soil (No. 6) 

 rests on the contorted surface of No. 5, occupying the hollows and 

 varying from 1 to 3 feet in thickness : it is merely the ordinary 

 rain-wash of the district. 



An examination of this section proves the threefold nature of 

 the deposits. The fluviatile shells, as well as the regular stratification 

 and the even sorting of the pebbles, show that the beds from 1 to 

 3, and perhaps 4, have been the deposits of fresh water undisturbed 

 by the presence of floating ice ; No. 5, on the other hand, by the 

 confusion of its bedding, the admixture of clay with sand and 

 gravel, and the presence of pebbles of chalk and of large transported 

 boulders of greywethers and of flint, is proved beyond all doubt to 

 be of glacial origin — to have been carried down by the ice and de- 

 posited, on its melting, upon the eroded top of the fluviatile deposits 

 below. According to Mr. Prestwich, " it is formed of reconstructed 

 London Clay and of gravel derived partly from the Boulder-clay.'* 

 This view may possibly be true (and its truth or falsehood does not 

 afl'ect my argument); but a careful examination compels me to believe 

 •that there is no proof of the derivation of this glacial deposit from 

 the wreck of the Boulder-clay, while on the other hand the clayey 

 nature of the bed was probably owing to portions of the London 

 Clay having been caught up by the ice in the higher grounds. The 

 Boulder-clay itself to the north of Brentwood may have been com- 

 posed precisely in the same manner. Whether or no this deposit 

 be a true Boulder- clay is in my opinion altogether an open question. 

 Its exact relation to the Boulder-clay to the north has not yet been 

 proved, and we can only be certain that, whencesoever it came, it 

 was transported by ice, and that it proves the climate under which it 

 was deposited to have been much more severe than that under which 

 the mammaliferous fluviatile gravels, free from ice- action, were 

 formed. At the top of all is the result of the atmospheric wear and 

 tear of the ground under temperate conditions of climate. 



The mammalian remains are found scattered throughout the beds 

 2 and 3, more abundantly however in the layers in which the heads 

 of Ehinoceros and Elephant occur. None of them presents any 



* Geological Magazine, vol. i. p. 245j 1864. 

 t Quart. Journ. Geol. Soc. vol. xsii. p. 553 et seq., 1866. 

 VOL. XXIII. PART I. I 



