Natural History. 39 



out into the Atlantic on the west, and land connected Scotland 

 with Greenland through the Faroes and Iceland on the north, 

 and with Scandinavia on the east. 



How far, and to what extent, the area between Gainsborough 

 and Lincoln was denuded during this great erosion, we shall 

 never know ; but as it rose higher and higher above the waves 

 the carving tools of nature were brought into play, and rain, 

 frost, and other forces of the atmosphere began their ceaseless 

 work. 



Now rain may seem but a weak agent for forming hills and 

 scooping out valleys, but, with the help of frost and the 

 corroding forces of the atmosphere, without doubt it effects 

 the task. 



Both hill and valley have one common origin ; they are the 

 remains of surfaces once planed and levelled by the sea, (I am 

 not here speaking of volcanic force), which, when raised above 

 the waves, were carved and cut into shape by the rain ; the 

 harder parts, the most capable of resisting erosion, forming the 

 hills, and the softer portions, the most easily denuded, forming 

 the valleys. 



Rising as vapour, mist, and cloud, and falling again on the 

 earth, rain is the source of all our lakes, springs, and rivers ; 

 and, through rivers, the source of continents also, by the 

 deposition of sediment on the floors of oceans and seas, and by 

 the silting up of shallow bays and estuaries. 



Its work never ceases, and, aided by frost and the chemical 

 components of the air, it penetrates and dissolves the hardest 

 rocks, and nothing is free from its action. Rivers can cut 

 only narrow channels, and it is left to rain to widen them into 

 valleys. No drop of rain runs an inch on the surface without 

 setting some soil in motion towards a lower level. 



The amount of erosion depends, of course, greatly on the 

 soil on which the rain falls. On clays, like those of the Lias, 

 it works far greater havoc than on sandy or gravelly soils ; 

 though, without due thought, the reverse might appear to be 

 the case. Mr. W. Whitaker of the Geological survey, in 

 discussing the age of man at the recent British Association 

 Meeting, well observed this when he said, "When rain falls 

 on gravel and sand, which are open and porous, they say ' Oh ! 

 come in, there's plenty of room,' and in it goes and comes out 

 again as a clear spring of water at the base ; whereas, when it 

 falls on clays and stiff soils, they say c We don't want you and 

 w e won't have you,' and the rain, in response, washes hundreds 



