GEOLOGY 



The existence of Devonian and Silurian rocks at a great depth under 

 the surface in this area is only known to us from borings made by the 

 New River Company in the valley of the Lea. These very old rocks 

 must for ages have formed a land-surface stretching right across Hert- 

 fordshire, and probably giving rise to rivers flowing to the north and to 

 the south. The shore-line of the Lower Greensand sea on the south 

 apparently ran through the north of London, and that of the contem- 

 poraneous northern sea through the north of Hertfordshire, trending 

 north-east and south-west, and communicating in that direction, through 



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