Pisolite

13 Sand 3 Clay Dark Blue Shale 14 Clunch Clay and Shale 15 Kelloway's Stone Cornbrash 16 Cornbrash 4 Sand and Stone 17 Sand and Sandstone 5 Clay 6 Forest Marble Forest Marble Rock 18 Forest Marble 19 Clay over Upper Oolite 7 Freestone Great Oolite Rock 20 Upper Oolite 8 Blue Clay 9 Yellow Clay 10 Fuller's Earth 21 Fuller's Earth and Rock 11 Bastard ditto and Sundries 12 Freestone Under Oolite 22 Under Oolite 13 Sand 23 Sand 24 Marlstone 14 Marl Blue Blue Marl 25 Blue Marl 15 Blue Lias Blue Lias 26 Blue Lias 16 White Lias White Lias 27 White Lias 17 Marlstone, Indigo and Black Marls 18 Red Ground Red Marl and Gypsum 28 Red Marl 19 Millstone Magnesian Limestone 29 Redland Limestone Soft Sandstone 20 Pennant Street 21 Grays Coal Districts 30 Coal Measures 22 Cliff 23 Coal Derbyshire Limestone 31 Mountain Limestone Red and Dunstone 32 Red Rhab and Dunstone Killas or Slate 33 Killas Granite, Sienite and Gneiss 34 Granite, Sienite and Gneiss

The above table contains a very complete classification of the British Mesozoic rocks, one of the Tertiary strata which is less complete, and a preliminary division of the Palæozoic rocks into Permian (Redland Limestone), Carboniferous (Coal Measures and Mountain Limestone), Devonian (Red Rhab and Dunstone) and Lower Palæozoic (Killas).

Since Smith's time the main work which has been done in classification is a fuller elucidation of the sequence of the Tertiary and Palæozoic Rocks, and this we may now consider.

The Mesozoic rocks are developed in Britain under circumstances which render the application of the test of superposition comparatively simple, for the various subdivisions crop out on the surface over long distances, and the stratification is not greatly disturbed. With the Tertiary and Palæozoic Rocks it is otherwise, for some members of the former are found in isolated patches, whilst the latter have usually been much disturbed after their formation.

Commencing with the Tertiary deposits we may note that "the first deposits of this class, of which the characters were accurately determined, were those occurring in the neighbourhood of Paris, described in 1810 by MM. Cuvier and Brongniart.... Strata were soon afterwards brought to light in the vicinity of London, and in Hampshire, which although dissimilar in mineral composition were justly inferred by Mr T. Webster to be of the same age as those of Paris, because the greater number of fossil shells were specifically identical[7]." It is to Lyell that we owe the establishment of a satisfactory classification of the Tertiary deposits which is the basis of later classifications. Recognising the difficulty of applying the ordinary test of superposition to deposits so scattered as are those of Tertiary age in north-west Europe, he in 1830, assisted by G. P. Deshayes, proposed a classification based on the percentage of recent mollusca in the various deposits. It may be noted, that although this method was sufficient for the purpose, it has been practically superseded, as the result of increase of our knowledge of the Tertiary faunas, by the more general method of identifying the various divisions by their actual fossils without reference to the number of living forms contained amongst them. The further study of the British Tertiary rocks was largely carried on by Joseph Prestwich, formerly Professor of Geology in the University of Oxford.