140 On some of the Strata in the Neighbourhood ofLondoUy 



numerous septaria which are dispersed through it, and by 

 the peculiar fossils which it contains. 



The difference of colour observed between its superior 

 and inferior part, and which has gcnevallv been supposed to 

 be owing to a diflcrence in the degree of oxidation of the 

 iron present in it, appears to be the result of a difference in 

 the quantit}' of it, occasioned by the washing away of this 

 iT)etal in the upper part by the water which percolates 

 through it, and which runs off laterally by the numerous 

 drains made near the surface. The dark-red colour of tiles 

 made from the blue clay, the reddish-yellow colour of the 

 place bricks made of the vcllowish-brown clay, and the 

 bright-yellow hue of the washed malms, those bricks which 

 are formed of the yellow clay which has been exposed to 

 repeated washings, are thus accounted for. 



The septaria lie horizontally, and are disposed at unequal 

 distances from each other in seemingly regular layers; and, 

 as has been just observed of the stratum itself, they become 

 of a paler colour, and it may be added suffer decomposition, 

 when placed so high in the stratum as to be exposed to the 

 action of percolating water. They frequently include por- 

 tions of wood pierced by the Teredines, Nautili, and other 

 shells; and it is a fact that may be worthy of being attended 

 to, whilst inquiring into their formation, that the septa of 

 calcareous spar frequently intersect the substances enclosed 

 in the septaria. 



Ti»is stratum is to be found not only wherever the pre- 

 ceding deposition extends, but in other parts also where 

 that has been removed. The cliffs of this clay, at Shepey, 

 extend about six miles in length ; the more elevated parts, 

 which are about ninety feet in height, being about four miles 

 in length, and declining gradually as they terminate towards 

 the east and west. 



The fossils of this stratum have been already carefully 

 particularised. A catalogue of those found at Shepey was 

 added by Mr. Jacobs to his Pluntce Favershamienses; and 

 an account of several of the fossil fruits found at Shepey 

 was i^ublished by Dr. Parsons in the fiftieth volume of the 

 Philosopliical Transactions. The fossils of IJampshiie have 

 been scientifically described by Dr. Solander, in the Fossilia 

 Hanloniensia of Mr. Brander, where the fossils themselves 

 are very exactly figured. 



It was not supposed, even after the publication of tliese 

 accounts, that the fossils of Shepey and those of Hampshire 

 were of the same stratum. Atnong the Hampshire fossils 

 no mention is made of crahs, lobslerSf torloiseSy nautili, 



nor 



