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12. — The Physical Structure of the London Basin, considered 



IN ITS EeLATION to THE GeOLOGY OF THE NEIGHBOURHOOD OF 



"Watford. 



By John Morris, F.G.S., 



Professor of Geology and Mineralogy in University College, London. 



[A Lecture delivered 14th October, 1875.] 



I HATE been requested by your Secretary to give to the Society, 

 in the form of a short lecture, some general observations on the 

 physical features of the London Basin, and I hope this evening to 

 lay before you some of those conditions under which the various 

 strata which constitute that basin were deposited, with the view 

 of attempting to explain the formations existing in the neigh- 

 bom-hood of Watford, and the adjacent parts of Hertfordshire. It 

 is well known that when the physical structure of any district 

 has been carefully worked out, as this has been by the assiduous 

 and ardent labours of Mr. Whitaker and Mr. Prestwich, it is com- 

 paratively easy for an ordinary geologist to say under what condi- 

 tions the various strata were formed and modified. 



In entering on the consideration of the physical structure of the 

 London Basin, we should regard it in several diiferent aspects : 



Firstly — Its general physical features. 



Secondly — The nature of the materials of which it is composed. 



Thirdly — The conditions under which these materials were 

 probably accumulated. 



Fourthly — The evidence afforded by the fossil remains as to the 

 climatal character of its several periods. 



Lastly — The successive and subsequent changes by which the 

 physical features of the district have been produced. 



Already you have had laid before you, in the perspicuous and 

 very interesting lecture by Mr. Lobley, the subject of the Chalk 

 formation. He has pointed out the conditions under which that 

 remarkable deposit of the British Islands was accumulated, and 

 informed you that that White Chalk, so marked a feature in British 

 geology, formed the last great group of the Secondary period. It is 

 true that the Upper White Chalk, as known in England, is on the 

 Continent overlain by a somewhat higher series than is represented 

 in this country, as the Maestricht beds, Faxoe limestone, and 

 probably the pisolitic limestone of France ; for these strata repre- 

 sent certain deposits towards the close of the Cretaceous era not 

 fairly represented in the British Islands. 



It will be well, however, to take our basis from the Chalk 

 formation, described by Mr. Lobley ; and, commencing from that, 

 we have a series of formations which constitute that third group 

 in British Geology known as the Tertiary series, or Caenozoic 

 period. This is subdivided into three or four groups, dependent 

 partly upon the nature of their fossil contents — in ascending order, 

 the Eocene, Miocene, Pliocene, and Pleistocene. They were long 



