A HISTORY OF HERTFORDSHIRE 



covered nearly 1,000 feet beneath the surface in south-east Herts has 

 the Devonian rock tilted 25 from the horizontal, and the Silurian 

 about 40. Whilst great changes in the relative distribution of land 

 and sea were taking place elsewhere in Britain during Carboniferous, 

 Permian, Triassic, and earlier Jurassic times, we have no evidence that 

 this tract sank entirely beneath the sea until we come to the Upper 

 Cretaceous period ; but the submergence of its north-western flanks began 

 in Upper Jurassic times ; in Lower Cretaceous the sea had reached 

 almost to its highest point ; and it was entirely submerged during the 

 whole of the Upper Cretaceous period, except perhaps towards the close 

 of the deposition of the Chalk. Whether it was a land-area whilst the 

 higher beds of the Upper Chalk were forming in the south of England, 

 and still later whilst the Maestricht Beds of Germany were being 

 deposited, we have no evidence to decide, but we do know that a vast 

 amount of chalk has been carried away. Most probably it is the higher 

 beds of the English Chalk only which have been removed by denudation, 

 Hertfordshire, with the rest of the British region, being above the sea 

 when the Maestricht Chalk was deposited. 



In early Eocene times Hertfordshire was again beneath the sea, 

 but not at first deeply submerged. Scotland, Ireland, Wales, and the 

 north and extreme west of England formed parts of a land-area from 

 which sediment was brought down by rivers flowing towards the west, 

 and for a time the climate was tropical. As the land again rose the 

 climate became temperate, and in the Miocene period there was much 

 volcanic activity in the north-west of Britain which probably caused some 

 disturbance of the strata in our area. In the Pliocene period the county 

 was apparently subjected to a vast amount of sub-aerial denudation, and 

 then the sea encroached upon it and its diversified surface was levelled to 

 a considerable extent into a plain of marine denudation. With the next 

 rise of the land the climate became of arctic severity and a great ice- 

 sheet came from the north as far as the range of London Clay hills, still 

 further levelling the land by its erosive action. Submergence followed, 

 and the climate became milder, but only to again become arctic with 

 partial emergence. As the land continued to rise however, and the 

 surface began to assume its present aspect, the climate gradually became 

 temperate, and the most important event of all in the history of the county 

 came to pass the advent of man by migration from the south. It 

 was at about this time also that England was finally severed from the 

 continent of Europe by the formation of the Straits of Dover. The 

 rainfall then was heavy, much of our present land was under water, our 

 rivers rose higher up their valleys and were often in flood, streams ran 

 down our present dry valleys or combes, and most of the county 

 was densely wooded. Man then, probably naked and living much in 

 trees by the margins of lakes or swamps, had to contend with the wild 

 beasts for existence with no other weapons than such as might be made 

 by chipping one flint with another; or perhaps to seek safety first in 

 climbing trees, and then, gaining some insight into constructive art, by 



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