Revieivs — Memoirs of the Geological Survey. 229 



an estuarine origin ; hence they have been termed the Upper 

 Estuarine Series. 



Evidences of unconformifcy, too, have been traced in the Midland 

 district, proving local upheaval and denudation, vsrhich probably 

 occurred when the Fuller's Earth and upper portion of the Inferior 

 Oolite were being deposited in the West of England, 



In the district more particularly described by Mr. Judd, the 

 Northampton Sand, with the Lower Estuarine Series, are often seen 

 lying upon an eroded surface of the Upper Lias Clay. 



The determination of the age of the Lincolnshire Limestone, first 

 surmised by the Eev. P. B. Brodie and Dr. Lycett in 1850, was not 

 adopted, because some confusion was made with the so-called "slates," 

 which, as Mr. Judd points out, occur at several horizons in the Oolitic 

 series. In 1866, he was led to regard the Lincolnshire Limestone as 

 of the age of the Inferior Oolite, and while engaged upon the Geologi- 

 cal Survey (1867-70) this view was confirmed on both stratigraphical 

 and palseontological grounds. And in this, additional corrobora- 

 tion has been furnished by the researches of Mr. Samuel Sharp and 

 Mr. Beesley. The variations in the attempted divisional line between 

 Middle and Lower Lias, based on palseontological evidence, are 

 discussed : such evidence proves that lines at different horizons 

 would be taken in different places ; and as the clayey beds of the 

 Lower Lias merge often imperceptibly into the sands and clays of the 

 Middle Lias, it is seldom possible to draw a definite line in the field. 



Mr. Judd's remarks on zones — strata marked by a general assemblage 

 of forms — are interesting : but zones can only be appreciated and 

 identified by long-continued palseontological research. There is 

 much perplexity in them. "It must be remembered too," says Mr. 

 Judd, "that every zone may present several fades; the petrological 

 and palgeontological features which characterize these being dependent 

 on the conditions under which the strata were deposited at different 

 points. The faunas of deposits belonging to two facies of the same 

 zone may differ from one another more widely than those of beds of 

 corresponding facies of different zones." 



The origin of the Northampton Sand forms an interesting and 

 important essay in itself, and was in 1869 communicated to the 

 Geological Society, and postponed (owing to official regulations) 

 for publication in this Survey Memoir. 



The descriptions of the Liassic and Oolitic strata are accompanied 

 by copious lists of fossils ; and an Appendix, prepared by Mr. 

 Etheridge, shows the distribution of the species. 



In the chapter on Post-Tertiary deposits are notes on Pre-Glacial 

 deposits ; Glacial deposits, including notices of large transported 

 masses of Inferior Oolite and Marlstone; Post-Glacial deposits, such 

 as Cave deposits, Valley gravels, Estuarine gravels. Marine gravels, 

 and Alluvium. 



Faults, Denudation and Scenery, Springs, Swallow Holes, etc., 

 likewise receive due treatment. The list of works relating to the 

 district, furnished by Mr. Whitaker, includes 110 different papers and 

 books. 



