46 Origin of the British Flora. 



give place to a higher race that tilled the ground and had 

 domesticated animals. These, however, are merely sug- 

 gestions ; for a systematic study of the deposits of this 

 stage also, at some point where they give a continuous 

 record, will probably solve the riddle. 



The Neolithic and later periods do not call for any 

 lengthy description. At first the land stood at an elevation 

 some 60 or 70 feet above its present level, so that many of 

 the river-valleys were cut to that depth below the sea, and 

 much of the English Coast was fringed with a broad strip 

 of alluvium, which probably almost connected our island 

 with Belgium and France. The climate during this epoch 

 was Temperate, for in the lowest ' submerged forests ' the 

 Oak is the most abundant tree. Then gradual and inter- 

 mittent submergence flooded the lower parts of the valleys, 

 and caused them to be silted up by the deposits of rivers 

 that no longer had sufficient fall to scour their beds. In 

 some of the peaty deposits or old vegetable soils that mark 

 stages of rest in their process of submergence, we find 

 polished stone weapons, and relics of cultivated plants and 

 of domesticated animals. The flora of these deposits, 

 however, is still very imperfectly known ; but all the plants 

 are species still found in Britain, though the occurrence in 

 South Wales in a * submerged forest ' of Najas marina, a 

 plant now confined to Norfolk, shows that the local 

 distribution may have been slightly different. 



Since the close of the Neolithic Period, changes in 

 physical geography have been slight, and have consisted 

 mainly in the continuous silting up of the flooded valleys, 

 and in the cutting back of the coast-line by the waves. 

 This latter process, it should be remembered, has been 

 sufficiently marked to increase the width of the Strait of 

 Dover, which in places is also being deepened by the 

 scour of the tides. When our present flora entered the 



