CHANGE OF LEVEL IN LANCASHIRE. 



437 



and to those accompanying my paper on the Post-Glacial Geology 

 of Lancashire and Cheshire, in the ' Proceedings of the Liverpool 

 Geological Society,' 1871-2, will explain the order and sequence of 

 the deposits ; and it will be seen that the last movement of the land in 

 Lancashire was downwards*. Submarine forests at the Alt mouth, 

 the Eimrose brook, the Liverpool and Garston docks show that sub- 

 sidence has taken place ; and (which is perhaps quite as good evidence) 

 sections of stream gullies, cut in the Boulder-clay and filled with 

 recent silt, at levels far below high water, are frequently met with 

 in dock-excavations. 



Upon the superior peat- and forest-bed, which is an extension 

 inland of the submarine forests, rests, as on a platform, some 22 

 square miles of blown sand, in some cases rising 75 feet above 

 Ordnance datum, and estimated by me to be at least 12 feet in 

 average depth. 



This deposit is shown in my map, as well as in that prepared by 

 the Geological Survey, by yellow dots ; it varies in width at dif- 

 ferent localities, its maximum being at Formby, where it reaches 

 3 miles inland. It is quite evident that the whole of this iEolian 

 deposit is an accumulation subsequent to the last subsidence of the 

 land ; therefore, if we can calculate the time it must have taken for 

 the deposit to form, we shall be in a position to determine the least 

 time that can have elapsed since the subsidence. 



The whole of the blown sand has been derived from the shore 

 between high- and low-water marks, but principally from between 

 high water of springs and neaps when the shore is dry. On a windy 

 day it is very curious to see the streaks of sand rushing over the 

 shore, even when it is damp, shining like rays of a lighter colour 

 pencilled over a dark ground. The shore is very flat, being in 

 places more than a mile wide between high- and low- water marks 

 of spring tides ; so that the conditions for the generation of subaerial 

 sand can hardly ever have been more favourable than they are now. 



In May 1866 I set out a plot of land at Blundellsands, in Burbo 

 Bank Road North, for building-purposes ; it had a frontage of 350 

 lineal yards to the sea, the western boundary being the then high- 

 water mark of spring tides. In 1874, for the purpose of enclosing 

 the said plot, I had to remeasure it to define the boundary, when I 

 found that high-water mark was considerably beyond the western 

 boundary, and that the sand had gained upon the sea. An open 

 wire fence was then put up on the original high- water mark, when 

 measurement showed that there were 15 yards of land in front of it 

 at one end, and 5 yards at the other. The high-water mark of 

 springs had, in fact, receded to that extent. I estimated the deposit 

 of sand that had taken place in the eight intervening years at an 

 average of 10 yards wide along the whole frontage and 2 yards 

 deep. Allowing 1 yard more in depth for sand that may have been 



* At Meols, in Cheshire, on the opposite side of the Mersey estuary, was a 

 Roman station ; and the land is now only a few feet above high- water ; therefore 

 the land cannot have risen since the Roman occupation. 



Q.J.G.S. No. 147. 2g 



