INTRODUCTION. iii 



end of Section A), another at Pettistree Hall, Sutton (see also Section A), another at 

 Ramsholt Cliff (on the Deben River, near Sutton), and the main mass which occupies 

 the parishes of Orford, Sudbourn, Iken, and Aldborough. To these may be added a 

 trace (not shown in the map) at Trimley, where it was observed in the digging of a 

 ditch by the late Mr. Acton. 



The Cor. Crag has long been known to consist of two main portions, and a third 

 subordinate bed. The first and lowest of these, (3' of Section XXII,) consists of a series 

 of calcareous sands, in some places more or less marly, which are rich in Molluscan remains. 

 The second, 3", consists of a solid bed formed of Molluscan remains, agglutinated with the 

 fronds and fragments of various species of Polyzoa into a rock, so hard as to have been 

 formerly quarried for building. The third and uppermost, 3"', is a thin subsidiary bed, 

 consisting of a few feet of the abraded material of the rock, reconstructed evidently in 

 very shoal water, probably, indeed, between tide marks, as it is very obliquely bedded. 



From the outliers at Tattingstone and Ramsholt this rock bed is absent, but over 

 the Sutton outlier a small cap of it remains. Over the main mass, however, it 

 spreads continuously, and either from a slight northerly dip of the whole formation, or 

 else from a displacement of the underlying shelly sands, this rock bed descends to the 

 sea level at the northern extremity of the area. The thickness of the formation has been 

 estimated at between eighty and ninety feet, but this seems to us to be much in excess 

 of the fact. The place to test the true thickness of the formation is clearly that where it 

 is in the greatest state of preservation. This is the neighbourhood of Sudbourn, at the 

 southern extremity of the main mass. The London clay, upon which it rests, comes out 

 along the Butley Creek Marshes, and the shelly beds in their full force appear along the 

 slope which fringes those marshes on the eastern side of the creek, where they are 

 exposed in several pits, known as the Gedgrave, the Gomer, the Broom, and the Hall 

 pits, from which the Mollusca of that neighbourhood are obtained. Higher up this 

 slope comes the rock bed, which forms the upper part of the low hills, and this is 

 exposed in numerous pits, that stretch away from those eminences to the northern 

 extremity of the formation. The outcrop of the shelly beds (3') along this slope is shown 

 in Section XXII. Now, it is clear, as it seems to us, that, the whole formation being 

 thus present in the complete state, we have only to take the elevation of the highest 

 points attained by the Cor. rock bed, 3", and its overlying reconstructed bed, 

 3'", in these parts, above the* elevation at which the London clay thus crops out at its 

 base, and the difference, after making allowance for any slight dip there may be, will be 

 the thickness of the entire mass. Estimated in this way, it will be difficult to make out 

 the thickness of the Cor. Crag as exceeding sixty feet. 



Mr. Prestwich has attempted to divide the shelly sands, 3', into constant and de- 

 terminable horizons, which he thinks might by investigation be identified by special 

 groups of fossils. We doubt the constancy or determinability of such horizons ; and, so far 

 from their being characterised by special groups of fossils, the author of the ' Crag Mollusca ' 



