FeatherstonhaugK's Geological Report. 



61 



pact limestone and calcareous grit, are independent of and in- 

 termediate between the chalk and the lowest known beds of 

 the tertiary. The developments of the tertiary beds are so 

 numerous in this country, that a similar passage may hereafter 

 be recognised here. 



The lower tei^tiary formation is subdivided into the Lon- 

 don clay and the plastic clay. The bed called plastic clay of 

 the English geologists is found, as well as that in the vicin- 

 ity of Paris, lying upon the chalk, yet the French deposite, from 

 which it takes its name, is a true clay, applicable to the plastic 

 uses of the potter, resembling the colored clays near New- 

 castle, Delaware, whilst the deposite in the environs of Lon- 

 don consists of beds of flint and pebbles alternating with sands 

 and clay, yet has received the name of plastic clay, because it 

 occupied the same geological position with the French deposite. 



The London clay is the great, dark-colored, argillaceous mass 

 upon which the city of London stands. Its mineral character, 

 however, varies : calcareous beds, with fossils, are enclosed in 

 it, with large septaria. Although these two clays have acquired 

 distinct names, yet there appears nothing in their mineral 

 character which warrants this distinction being kept up, or 

 their being considered other than as a series of clays, where 

 the fossils preponderate in the upper part, and the sand and 

 pebbles in the lower. This is the eocene group of Mr. Lyell, 

 a compound Greek term, expressive of the dawn of the present 

 order of nature, a small proportion of the fossils contained in 

 it belonging to species now found living. 



The middle tertiary or miocene beds have their best type 

 in France, and comprehend the lower fresh-water, the upper 

 marine, and the upper fresh-water of the vicinity of Paris. 

 The lower fresh-water contains siliceous limestone, with gyp- 

 sum and the bones of the paloetherea and other extinct ani- 

 mals, and fresh-water marls. The upper marine consists of 

 gypseous marls, sands and sandstones, and marine marls and 

 limestone. The upper fresh- water contains millstone without 



