198 



HARDWICKE'S SCIENCE-GOSSIP. 



GEOLOGICAL LESSONS AMONG THE 

 SANDHILLS. 



By T. Mellard Reade, C.E., F.G.S., &c. 



AS enabling the student of geology to realise 

 some of the phenomena of physical geology, 

 observations among the sand dunes may be of con- 

 siderable use. A residence near the sea, on land as 

 it were reclaimed from the desert, a stretch of blown 

 sand extending along the coast from Liverpool to 

 Southport, has directed my attention more particularly 

 to the subject. I will proceed to classify and describe 

 some of the miniature examples of geological action 

 that have come under my observation. 



River action. — The sandhills, here loose, there held 

 together with "bent" or starr grass, or covered 

 with a growth of dwarf willow on the inner plateaux 

 or " flats," form a rampart which holds up the 

 contiguous inland drainage. This rampart is only 

 broken by streams having their rise in the " uplands " 

 beyond the confines of the sand belt — such as the 

 rivers Alt and Douglas and some smaller streams. In 

 very wet winters such as the last months of 1880, when 

 4"50 inches of rain fell in October, 4'Oi in November, 

 and 5 '63 in December, the rainfall unable to escape 

 by saturation, evaporation and soaking through the 

 sand on to the shore, ponds up in considerable 

 flashes. On two occasions only during a residence 

 of thirteen years, I have noticed a considerable 

 stream of water issuing from between the sandhills 

 at a place that is usually dry. Following up the 

 course of this stream I found it winding about among 

 the valleys between the sandhills, cutting out vertical 

 bluffs and perfect carions which showed on their 

 sides the stratification of the sand due to wind action. 

 In some places it was quite narrow and winding, in 

 others it opened out into miniature valleys. To a 

 Lilliputian it would have appeared a mighty river ! 

 Eventually I traced it to its source, a lake, formed 

 by the rains, which had risen sufficiently to burst its 

 banks and by its flow cut out the " scenery " I have 

 described. Since the frost came on, the stream no 

 longer flows ; in its bed is ice, covered with snow, 

 and the frozen sand stands out in tiny rugged cliffs 

 simulating rock to perfection, 



A zvaterfall. — Thornbeck Pool is a stream flowing 

 from the "uplands" of Great Crosby. It drains 

 about 1480 acres, and has made a way for itself 

 through the sandhills into the river Alt, where the 

 latter winds about for several miles on the shore 

 flowing southwards towards the mouth of the Mersey. 

 The river Alt itself is an interesting phenomenon. 

 It flows from the uplands of West Derby, and at 

 Sefton enters the moss country, winding through 

 it until it reaches the Altcar-rifle range, which is 

 a plain bordered by sandhills on the sea side, and 

 by the river Alt on the landward side. The range 

 itself has been to a large extent reclaimed from the 



sea, by the Alt commissioners, protecting their river 

 from blowing sand by hurdles and furze, and the 

 sand getting deposited seawards of these obstructions. 

 The old Crosby lighthouse stands a lone object on 

 the banks of the river, looking on a small scale more 

 like an Egyptian monument by the Nile than anything 

 else. Where the Alt flows through the moss land, 

 it has built up its banks by continual overflows 

 (before the last embankment works were carried 

 out) and by the deposition of alluvium near to the 

 river. The course of the Alt on the shore, within 

 the last few years has altered very considerably, 

 it bends in now with a great sweep towards the shore 

 at the point where the Thornbeck Pool joins it. The 

 effect on the latter is striking. Formerly the stream 

 trickled over the shore in a shallow channel, but of 

 late years it has been cutting its way back from the 

 Alt in a deep trough, the stream tumbling over a 

 vertical cliff of blue clay capped with hard peat, like 

 a veritable Niagara. The resemblance of this tiny 

 waterfall to the colossus of the American continent 

 does not cease here, for the spray of its fall combined 

 with the effect of the tide, eats away the soft clay 

 beneath, leaving the peat overhanging as a shelf 

 until it can support itself no longer, when down it 

 goes into the gulf below in masses to be gradually 

 washed away. In this way it has cut a deep gully 

 reaching nearly to high-water mark. In November 

 1877 175 inches of rain fell in twenty-four hours. I 

 have a coloured sketch I made of this waterfall on 

 that day, it presented so remarkable an appearance. 

 It has been receding at the rate of 5^ yards per 

 annum during the last two years. 



Wind, Drift, and Demidation. — From having had 

 occasion to determine the boundaries between the 

 townships of Great and Little Crosby, my attention 

 was specially directed to the course of the Thornbeck 

 Pool in old times. According to the maps reaching 

 back to the year 1 702 it formed the boundary between 

 the two townships. A new cut was made, and the 

 stream turned down a culvert some fifty years ago. 

 Since then the old stream course has been buried in 

 blown sand, though some of its former effects are 

 recognisable even now, and account for some of 

 the surface features which before were a mystery to 

 me. By digging at a particular point we came upon 

 a bridge which was shown on the original maps, thus 

 verifying their accuracy. Before this stream was cul- 

 verted, I have no doubt it would act like the little 

 river among the sandhills first described. That is, 

 the land drainage would back up in the low part, 

 forming the moss land which exists on its course, 

 and though the drainage area would be sufficient to 

 keep it always more or less open, I have no doubt it 

 would fluctuate, pond up, and then burst its banks 

 again. 



The form of the sandhills is due to the wind, which 

 alternately heaps up the sand and cuts it down 

 again. The origin of the sand is the seashore. 



