A HISTORY OF LANCASHIRE 



addition to those mentioned. Sections in the Boulder Clay can be seen almost everywhere, and are 

 especially marked on the coast, where at times they form cliffs, as at Blackpool, from 40 to 70 feet 

 in height. 



One interesting feature of the Lancashire drift which still requires working out is the occur- 

 rence of broken and comminuted shells, and isolated valves. These are found even in the inland 

 clays. Amongst others, the writer has found valves belonging to species of Cardium, Mactra, 

 Alytilus, and a portion of the test of an Echinoderm. Foraminifera also occur. 



In many places the drift can be divided into three parts, a middle division of sand being inter- 

 calated between lower and upper Boulder Clays, or Drift. Pockets of sand, sometimes of large size, 

 at times occur interbedded with the clays.i 



Post-Glacial Deposits. — To this category belong the extensive peat deposits of the moorlands and 

 plains, which are often of considerable thickness, especially in the ' Mosses,' as Chatmoss, etc., and 

 contain trunks and stumps of trees, sometimes in such profusion as to indicate that many districts 

 and even hills were densely wooded instead of bare and bleak as we now see them. 



Here also must be placed the banks and deposits of Alluvium at the mouths and along the 

 sides of many of the rivers, and the extensive dunes and sandhills which are so striking a feature 

 of the coast between the mouths of the Mersey and the Ribble, near Blackpool, and at Walney 

 Island. 



In the neighbourhood of Fleetwood, Poulton, and Blackpool, these later deposits have been 

 classified by the officers of the Geological Survey as follows : — 



Post-Glacial 



Recent 



Pre-historic 



Blown Sand . 



Upper ' Cyclas ' clay, sand, etc. 



Upper ' Scrobicularia ' clay. 



Marsh clay and tidal alluvium Peat. 



Lower ' Cyclas ' clay. 



Lower ' Scrobicularia ' clay. 



Presall Shingle. 



A somewhat similar division holds good for the district around Southport, the place of the Presall 

 Shingle being taken by the Shirdlcy Hill Sand and Lower Peat. 



BLOWN SAND 



Sandhills are forming so extensively along the Lancashire coast that a few words need to be 

 written respecting them. The set of sea currents is such along the coast from north of Liverpool 

 to Fleetwood that almost continuous sandy beaches are formed. Indeed, these have accumulated in 

 some places to such an extent that the sea appears to be retiring from the land. This is well seen 

 at Southport, where marine lakes and promenades take the place of what was once open beach swept 

 by every tide. The exposure of the sandbanks at low tide to the sun results in the upper layer of 

 sand becommg dried, when it is easily moved by the wind and swept inland, where it collects against 

 any obstacle, such as fences or buildings, and accumulates until it at length overtops them, and falls 

 over upon the other side. In this way a low eminence is formed, which is continually being added 

 to on the seaward side and as continually being reduced by the surface being carried further inland. 

 In this way an extensive belt of arable land has been covered over, and the encroachment has 

 become so serious that vigorous attempts are made to stop its further progress by planting ' starr- 

 grass,' Psamma arenaria, and Ammophila arundinacea, whose long-matted roots hold the sand together, 

 whilst the leaves protect the surface. Southport is entirely built upon blown sand, which can also 

 be seen inland behind it. 



At Formby the sandhills are three miles in width, although it is stated that none existed so late 

 as 1690, the whole deposit having been formed since by the silting up of the then Formby Harbour, 

 and the formation of a sandbank against the land, from which the loose sand was carried landwards. 

 Between Formby and Birkdale, near Southport, many farms have been entirely covered up within 

 the last hundred years, and houses completely buried. 



The sand often contains shells and shell fragments, which have been also wind-borne, and, these 

 decaying, the carbonate of lime of which they consisted becomes dissolved in the acid-laden rain, 

 and, being afterwards reprecipitated, it serves as a cementing material to the sand, which thus becomes 

 solidified, and even impermeable to water. Between Fleetwood and Rossal the sand is extremely 

 large-grained. 



1 There is a considerable literature dealing with the Glacial Drifb, and we are indebted especially to 

 Mr. T. Mellard Reade, Mr. R. H. Tiddeman, and Mr. C. E. De Ranee for records of fecu and 

 explanations. 



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