FOSSILS IN LONDON CLAY. 



221 



The bones of horses, with the tooth of an elephant, have been 

 found in a bed of unctuous clay, resting on chalk, near Margate ; 

 but as the clay is superficial, it may be a diluvial formation. 



In France, near d'Auteuil, and south of the Dordogne, according 

 to Humboldt, bones of vertebrated land animals are found in a for- 

 mation resting on chalk, analogous to the plastic clay. Baron Cu- 

 vier says, however, that he has not discovered the bones of land 

 quadrupeds, in any strata below the calcaire grossier, which covers 

 the plastic clay. But, neither the plastic clay nor the gypsum beds 

 of Paris can be taken as types of the tertiary strata in other countries. 



The London clay is placed over the plastic clay and sand, and is, 

 in fact, an upper member of the great arenaceous and argillaceous 

 formation that covers chalk. Some geologists attempt to identify the 

 London clay with the beds of calcaire grossier, and of gypsum, in 

 the Paris basin, but their mineral characters are most essentially dif- 

 ferent. By attempting to force an agreement with artificial classifi- 

 cations, where it does not exist, we mystify what is clear and simple, 

 and retard the progress of knowledge. 



The uppermost bed of the London clay is of a reddish brown col- 

 our, and is more arenaceous than the lower beds : the colour of the 

 lower beds varies from a bluish lead colour, to a blackish brown ; 

 they are often considerably indurated, and have somewhat of a slaty 

 structure. The thickness of the London clay varies from one hun- 

 dred to four hundred feet or more : this variable thickness is occa- 



called calcareous. In the Valley of les Echelles, the immediate junction of the 

 limestone with the sandstone may be seen, soon after entering the valley form the 

 archway. This vast wall of limestone, nearly one thousand feet in thickness, rests 

 upon a mass of sandstone of unknown depth : there is very little dip, where the 

 first junction is seen, but about a mile below, you meet with the limestone again in 

 conjunction with the sandstone, and thrown into a vertical position. The work- 

 men whom I met with, near the mouth of the gallery, said they always found sand- 

 stone below the limestone, and they considered it as the lowest bed in the country : 

 but this is obviously a mistake. The sandstone, or molasse, on which the lime- 

 stone in this part of Savoy reposes, or which is subordinate to the limestone, is 

 composed of smallish grains of quartz and chlorite, pretty equally mixed. In the 

 sandstone of les Echelles, which I got from its junction with the limestone, there 

 were some particles of rose quartz and mica. It scratched glass, strongly, when 

 rubbed upon it ; but when put into a dilute muriatic acid, it effervesced, violently, 

 and became friable, owing to the solution of the calcareous cement by which it ap- 

 pears, from this experiment, to be agglutinated. The molasse, which is inter- 

 stratified with limestone and associated with coal on the lake of Annecy, also ef- 

 fervesced ; but, the particles being smaller, it appeared nearly homogeneous, when 

 examined without a lens. It has been recently stated, that the molasse of the Alps 

 belongs to the same formation, as the sandstone above chalk near Paris. There 

 may be sandstone of that formation in the canton of Berne; but the molasse or 

 sandstone in this part of Savoy, I am well convinced, is a member of formations 

 that are lower than chalk. It is possible, however, that beds of this molasse may 

 have been worn down, during the great destruction of the strata, that has evidently 

 taken place since they were deposited, and from the debris of this sandstone, upper 

 beds may have been formed covering strata that are above chalk. The molasse 

 which covers the bones and teeth of the mastodon and other large mammalia, 

 near Alpnach, nearly resembles that in this part of Savoy ; but the particles are 

 smaller, and more intimately mixed."— P. 176. 



