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formatiou, the Loudon Clay, although to a great extent covered 

 by Drift deposits, forms by far the larger portion of the beds on 

 which our district stands. The hills in many parts of Essex — 

 such for instance as the ridge extending from Chingford to 

 Waltham Abbey and the range about Havering-atte-Bower 

 and Brentwood — are entirely of London Clay, in many cases 

 capped with outhers of Bagshot sand and Drift formations. 

 We have but to call to mind High Beech in our own neighbour- 

 liood to see that the most picturesque features of the county 

 are due to this formation. Sections of the London Clay, 

 wliich is about 420 feet thick in the neighbourhood of the 

 metropolis, have been exposed in Essex at Buckhurst Hill, 

 Th'eydon, Brentwood, Stifford, Upminster, Warley, &c., and 

 sections of this formation showing its junction with the 

 Woolwich and Eeading beds have been exposed at Bishop 

 Stortford and Roydon. The Middle Eocene period is repre- 

 sented in our county by the Bagshot Sands already alluded 

 to, which form outliers capping many of our hills, such 

 as at High Beech, Crabtree Hill near Lambourn, South 

 Weald, Havering, Blackmore, and large patches stretching 

 northwards from Warley Common to beyond Brentwood 

 and again about Kelvedon Hatch, One other very interest- 

 ing formation of Pliocene date — the Crag — just commences 

 to appear in the north-eastern corner of the county at Man- 

 ningtree, south of the Stour valley, and Walton-on-the-Naze 

 has furnished Red Crag fossils of special geological interest. 



At about that period of the earth's history when the Crag 

 formations were deposited, our globe, owing to a certain com- 

 bination of astronomical events, began to experience those 

 great climatic changes which resulted in the Glacial Period, 

 during which the whole of the northern portions of Europe 

 and America were laid under an icy covering of great glaciers 

 which flowed down from all the mountain slopes and high 

 lands, levelling up the valleys, and becoming confluent, formed 

 a gigantic ice-sheet, which extended southwards into regions 

 which now enjoy a temperate climate, whilst floating icebergs 

 and rafts drifted even into tropical seas, and there thawing, 

 scattered their accumulated burdens of rock fragments and 

 miscellaneous cUhris over the sea bottom. The Glacial Epoch, 



