Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/309

 sandy, and blackish. The sand dividing them is also said to vary in colour like the plastic clay itself, from white, grey, and yellow, to grey mixed with red and pure red. The English beds of plastic clay and the sands attending them at Reading, Corfe Castle, and Alum Bay, exhibit analogous variations in colour and consistency; indeed at the latter place they run through almost every possible combination in the scale of colours. Between the upper plastic clay and calcaire grossier of Paris, there is also stated to be sometimes found a bed of sand of irregular thickness, which they are doubtful whether to consider as belonging to the formation of plastic clay or calcaire grossier, but are rather inclined to attribute it to the former. It contains organic remains in very few places. Is it not improbable that this bed is contemporaneous with some of the upper strata of the plastic clay formation which we find at Loam Pit Hill, at Blackheath, and in the Isle of Wight, at which last place the beds belonging to this series are accumulated to a thickness far greater than has been yet noticed in any other spot, amounting at Alum Bay, according to Mr. Webster, to 1131 feet, interposed between the chalk and London clay.

Viewing it on the great scale then we may consider this formation, which has been characterized by the title of plastic clay, as composed of an indefinite number of sand, clay, and pebble beds, irregularly alternating. Of these, the sand forms in England, the most extensive deposition, in which the clay and pebbles are interposed subordinately and at irregular intervals.

Again, the occurrence of organic remains in the different beds of this formation, is like the alternation of the strata composing it, exceedingly irregular: sometimes they occupy the clay, at other times the sand or pebbles, and very frequently are wanting in them all.

A good example of shells occurring, mixed with large pebbles,