Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/892

 In 1846, Prof. E. Forbes published the names of certain shells he had found in the Lancashire drift, amongst others a Dentalium from Preston *.

In 1862, Mr. Hull†‡ described the results of the mapping of 600 square miles of drift around Manchester, which necessitated a modification of Mr. Binney's classification, a Boulder-clay resting on the upper sand and gravel, and the lower sand and gravel being often absent.

Recent   Valley-gravels and River-terraces. Upper Till, or Boulder-clay.

Drift    Middle Sand and Gravel. Lower Till, or Boulder-clay.

Form of the Ground in Western Lancashire and Cheshire.

Undulating plains (of Triassic and Upper Carboniferous rocks), more or less covered with glacial drift, occupy the country between Liverpool and Chorley, westward of which a low plain covered with peat-moss borders the sea-coast.

Between Chorley and Lancaster the rock surface is extremely low, often, indeed, beneath the sea-level ; but beds of glacial drift, often 150 feet in thickness, are piled up on it, forming a slightly inclined plane, dipping from the Pendle range towards the sea, where it forms a line of cliffs near Blackpool from 40 to 80 feet in height. This drift plain has been cut through, to a greater or less extent, by various brooks, streams, and rivers. Few, however, have reached the rock surface beneath, the Bibble and its tributary the Darwen being almost the only exceptions.

The third area into which Western Lancashire and Cheshire may be divided consists of three extremely low tracts, in which not only the rock surface, as in the Preston district, lies below high-water mark, but in which the glacial drifts themselves have been denuded away, so that the sea has to be kept out by sea-walls and banks, and is daily making encroachments. They are all areas of former obstructed, and present artificial drainage, and are deeply covered with peat-moss, which reaches in one instance a thickness of 30 feet. The first district is the low country between Lancaster and Fleetwood, lying on both sides of the river Wyre ; the second stretches from the river Alt, north of Liverpool, to the river Douglas, north of Southport; and the third lies between the rivers Dee and Mersey, in that part of Cheshire known as the peninsula of Wirral. It is traversed by a small stream, called the Birket, falling into Wallasey‡ Pool, a tributary of the Mersey, and bounded to the south by an escarpment hereafter to be described.


 * Mem. Geol. Survey, vol. i.

† Trans. Man. Lit. & Phil. Soc. vol. ii. (3rd series), p. 451. Mem. Geol. Sur., Country around Oldham, 1864.

‡ Pool, in this district, is synonymous with " brook ;" thus Bromborough Pool, Liverpool, Blackpool.