74 S. V. WOOD, JTJN., AND F. W. HARMER ON THE 



5. Observations on the Later Tertiary Geology of East Anglia. 

 By Searles V. Wood, Esq., jun., F.G.S., and Frederic W. 

 Harmer, Esq., E.G.S. ; with a Note by S. V. Wood, Esq., F.G.S., 

 author of the ' Crag Mollusca,' on some New Occurrences of 

 Species of Mollusca in the Crag and Beds superior to it. 

 (Head November 8, 1876.) 



Contents. 



1. The unfossiliferous sands of the Bed Crag. 



2. The unconformity between the Lower and Middle Glacial beds ; and the 



interglacial valley-excavation. 



3. The consideration of the mode in which the Middle Glacial series was 



accumulated, and of the way in which the sequence of the beds 

 posterior to the Lower Glacial series is to be traced. 



In writing the Introduction to the ' Supplement to the Crag Mollusca/ 

 issued by the Palseontographical Society (for 1871), our object was, 

 with the help of the Map and Sections accompanying it, to give only 

 such a compressed or synoptical account of the researches on which 

 we had for several years been engaged as would enable geologists 

 to perceive the results at which we had arrived respecting the suc- 

 cession of the beds posterior to the Crag in the East of England. 

 We considered that as the officers of the Geological Survey had com- 

 menced the examination of the district, and would eventually publish 

 a detailed account of the sections and other evidence bearing upon 

 that succession, we should have only encumbered scientific publica- 

 tions by bringing forward in greater detail the physical evidence 

 which we had collected, and which had led us to the conclusions of 

 which we thus gave a representation, the evidence of organic remains 

 which we had collected being given by the author of the ' Crag 

 Mollusca ' in the tabular lists which accompany the Supplement to 

 that work. 



There are, however, some subjects referred to in that " Introduc- 

 tion" upon which w T e have made subsequent observations that we 

 desire to bring forward ; and there is one in particular upon which 

 we touched only slightly, the break between the Lower and Middle 

 Glacial deposits, which from its geological importance it is desirable 

 should be shown in some detail, in order that while the officers of 

 the Survey are engaged upon the district it may receive from them 

 the scrutiny which it merits. 



1. The Unfossiliferous Sands of the Bed Crag. 



The first subject on which we have to remark is that of the un- 

 fossiliferous sands overlying the Red Crag. These sands have 

 long been a subject of perplexity to one of us ; and in reference to 

 them we observed, in the before-mentioned "Introduction" (p. viii), 

 that " we did not think they represented the Chillesford sands, as 

 they neither contained the Chillesford shell-bed, nor, though some- 



