40 



tion of the mass. At Hampstead, the calcareous ingredient exists 

 in large proportion and in a finely divided state. Frequently, one 

 or more thin layers of the oyster shell peculiar to the lower tertiary 

 region occurs in the body of this stratum; a fact remarkably exem- 

 plified at Piping Tree, and for nearly a mile further down the river, 

 where the layer of shells froms a hard rocky shelf laid bare at low 

 tide, and presenting large and perfect specimens of the fossil oyster, 

 in the midst of the greenish stratum just described. 



At Chericoke the stratum rises to about four feet above the water, 

 and as ascertained by digging, descends to seven feet below the 

 river shore. 



Higher up the stream, these strata attain a greater elevation, and 

 subjacent beds, not apparent at cither of the points above described, 

 come gradually into view. In these localities we usually find, 



1st. A layer of dark grayish-green or grayish-brown colour, con- 

 taining multitudes of shells, generally in a perfect state; the fossil 

 oyster shell already referred to abounding chiefly in the upper part 

 of the stratum. Beneath this, but frequently separated by no dis- 

 tinct line of demarkation, we find, 



2d. A layer of darker hue, containing less shelly matter, and the 

 shells chiefly of the smaller kinds ; and 



3d. A stratum of the same appearance, in which no calcareous 

 matter can be discovered. 



All these strata contain a large portion of the greensand. In the 

 upper and lighter-coloured beds, the granules of this substance are 

 very obvious to inspection, resembling in size and colour the grains 

 of gunpowder, and giving when bruised a bright green stain. In 

 the lower beds they are more minute, and being intimately mingled 

 with the other materials present, are not readily recognised, except- 

 ing by the general greenish character of the mass. These beds also 

 contain a great deal of Mica in fine sparkling scales. Of the depth 

 of these strata below the level of the river nothing definite is known, 

 no extensive excavations having yet been made. At Mr. Wick- 

 ham's they are found to rest upon a layer of large pebbles, but this 

 basis is perhaps not co-extensive with the deposite lower down the 

 river. 



When the upper bounding surface of the Eocene is even and uni- 

 form, it is always marked by a thin layer of black pebbles, upon 

 which there usually rests a bed of olive-coloured earth, or of friable 





