228 Reviews — Memoirs of the Geological Purvey. 



The denudation of tlie Weald is ably treated of, and the author, 

 with the benefit of matured reflection, has been able to confirm the 

 theory put forward ten years ago by Dr. Foster and himself. This 

 theory, advocated also by Prof. Eamsay and others, is that of long- 

 continued subaerial action on an ancient "plain of marine denuda- 

 tion." 



The origin of the Wealden Beds is discussed, and the evidence 

 would seem to show that they were fluviatile accumulations de- 

 posited in a lake. Lastly, Economic Geology, Ironworks, Coal, 

 Springs and Water Supply, Building Stones, Eoads and Eoad 

 Material, Limestones, Manures, and Clays, and the Geological Dis- 

 tribution of Population and Disease, receive a considerable amount 

 of attention. 



Lists of Fossils, revised by Mr. Etheridge, are given in an Appen- 

 dix; which also contains an exhaustive list of books, papers, etc., 

 relating to the Geology of the Wealden area, altogether numbering 

 564. 



The work is well illustrated with maps and sections. 



II. — Mr. Judd's Memoir is devoted to a description of the Liassic, 

 Lower and Middle Oolitic rocks, from the Lower Lias to the Oxford 

 Clay inclusive, with notes on the superficial gravels and recent 

 alluvial, estuarine, and marine deposits. 



His Introductory Essay, on the classification and correlation of the 

 Jurassic rocks of the Midland District of England with those of other 

 districts, will prove of the highest interest to all students of Geology, 

 for it contains the result of much original thought. 



The variations in lithological character, and in fossils, of the 

 several divisions of the Oolitic series, are well illustrated and 

 described by Mr. Judd. The great limestones are of but local 

 development, as is the case with the limestones of the Palaeozoic 

 series, and when absent their partial or perhaps total replacement 

 by strata of varying lithological character renders exact correlation 

 a matter of some difficulty. It becomes necessary to adopt different 

 classifications in different tracts of country, which are essentially 

 based on lithological characters. Thus the Northampton Sand in 

 North and East Oxfordshire and South Northamptonshire fills up 

 the interval between the Upper Lias Clay and the Great Oolite 

 Limestone. Palagontologically the upper part of the Sand is con- 

 sidered as representing the lower zone of the Great Oolite, while' the 

 lower portion of the Sand is considered as the equivalent of the 

 lower beds of the Inferior Oolite. 



The Midford Sand of the south-west of England would seem to be 

 partly homotaxeous with the Northampton Sand. In the Vale of 

 Moreton, Mr. Judd thinks it possible that the Midford Sand which 

 underlies the Inferior Oolite series either thins out altogether in the 

 northern spurs and outliers of the Cotteswolds, or its attenuated 

 representative is lost in the Northampton Sand. 



He has been enabled, in jolaces, to separate portions of the 

 Northampton Sand of Great Oolite age from that of Inferior Oolite 

 age ; the upper beds consist of sandy clays, and present evidences of 



