132 On some of the Strata hi the Neighbourhood of London i 



covered in any ot 'he superincumbent beds: that some fos- 

 sils, which abound in the lower, are found in diminishing 

 numbers through several of the siiiierincunibtnt, and arc 

 entirely wanting in the uppermost strata: that some fossils, 

 occurring in considerable numbers in one stratum, become 

 very rare in the adjacent portion of the next superincum- 

 bent stratum, and afterwards are lost : that fossils of one 

 particular genus, which exist abundantiv in the lower strata, 

 and occur in several of the superincumbent ones, are not 

 found in the three highest strata ; whilst one species of that 

 genus, hut which has not been found in a fossil state, ex- 

 ists in our present seas: and lastly, that most of tlie remains 

 which are abundant in the superior strata, are not at all 

 found in the lower. These general facts lead us to hope, 

 that geology may derive considerable assistance from an 

 examination of fossils, made in connexion with that of the 

 strata to which they belong. 



The following is an attempt to investigate on this plan 

 some of the upper strata in the vicinity of the metropolis 

 with their contained fossils; and, although by no means 

 complete, it will, it is hoped, induce others, who possess 

 superior abilities and opportunities, not only to re-examine 

 more correctly these strata, but to extend their researches 

 to the subjacent strata. 



The whole of this island displays evident marks of its 

 stratification having, since its completion, suffered consi- 

 derable disturbance from some prodigious and mysterious 

 power. By this power all the known strata, to the greatest 

 depths that have been explored, have been more or less 

 broken and displaced ; and in some parts have been so lifted, 

 that some of the lowest of these have been raised to the 

 surface J whilst portions of others, fo a very considerable 

 depth and extent, have been entirely carried away*. From 

 these circumstances great difficulties and confusion fre- 

 quently arise in examining the superior strata: the counties 

 however immediately surrounding the metropolis, as well as 

 that on which it stands, having suffered least disturbance, 

 are those in which an investigation of these strata may be 

 carried on with the smallest chance of mistake. 



Real alluvial fossils, washed out of lifted or original su- 

 perior strata by strong currents, and which in other parts 



* See several essavs on this subject in tlie Pliilosophical Magazine, by Mr. 

 Farey, and the Report on Derbysliire, vol. i. p. 10,5. 



Also A Letter on tlie Alteralioi::. which h.ive taken place in the Structure 

 of Rocks, on the Surface of the Basalt'c C'ountrv in the Counties of Derry 

 and Antrim, by William Richardson, D.D. Phil. Trans.. 1S03. 



are I 



