512 H. W. Monckton — Gravel-Flats of Surrey and Berks. 



favourable. There is often, therefore, at the head of the fjords 

 a shallow which is called or. It ends abruptly a little distance out 

 with a steep slope, where the water all at once becomes some 

 fathoms deep. 



Suppose, now, that the land is raised up ; we shall have a long, 

 slightly sloping plain of sand and clay, with an abrupt steep slope 

 where the deep water was. The river will at first throw itself over 

 the steep slope as a waterfall, but by degrees it will cut down into 

 the plain and begin to form a new shallow out of the materials. 

 The terraces are just such plains, with so gradual a slope up above 

 the floor of the valleys that they appear horizontal, and ending 

 outside with a steep precipice. At the mouths of most of the 

 valleys, one sees many such terraces rising staircase-like one above 

 the other. These terraces seem to show that the land has rapidly 

 risen many feet at a time, a rise for each terrace, and between them 

 have been long periods of repose, during which the or were formed. 



The above is roughly translated from a small Norwegian school 

 geology by Corneluissen, and seems to me to afford a good 

 explanation of the step-terraces of Norway ; but does it not also 

 explain the gravel-flats of England ? It seems to me that short, 

 rather rapid elevations, separated by long periods of repose, would 

 produce precisely the result which we see in Surrey, Berkshire, and 

 other parts of the country. 



The flats are due partly to excavation and partly to deposition. 

 Assume that an elevation of the Thames Valley to an amount of 

 20 feet took place now. The river would at once begin to cut 

 down its channel to the new level, and in our soft strata its progress 

 back from the sea would be very rapid. We should have a new 

 plain excavated, and the gravel now at the level of the river 

 alluvium would stand up as a terrace ; part of it would, moreover, 

 be destroyed, and the materials spread out as a gravel sheet at 

 the lower level. In England, where the rock is soft and easily 

 eroded, the gravel-flats are wide-spread, but in many of the 

 Norwegian valleys the rock is very hard, and the terraces are 

 consequently of very limited extent. 



The gravel-flats are best seen on the south of the Thames. North 

 of that river similar flats occur, but there drift questions are much 

 complicated by the presence of glacial beds ; indeed, the elevation of 

 the south of England and the deposition of most of the gravels 

 appears to have taken place whilst the north of the country was 

 under glacial conditions, and after they ceased the country seems to 

 have undergone but little further elevation. In Norway, on the other 

 hand, movements of elevation seem to have taken place from time to 

 time up to a much more recent date, and so we find the step-terraces, 

 which are post-Glacial and were formed after southern England 

 had entered upon a period of repose. 



The gravel beds upon these flats differ materially from most or all 

 of the older geological deposits of this country. The fact that the 

 stones are to a large extent subangular, and but little water-worn, 

 distinguishes them from the Eocene pebble beds; nor do they resemble 



