262 J. F. BLAKE AND W. H. HTJDLESTON ON 



prepared to assert it without a careful examination of the great 

 uniform clay series in which no Corallian beds are found. Our aim 

 at present will be to take such note of the physical conditions under 

 which each deposit was formed as will enable us to estimate the 

 contained fossils at their true chronological value, as well as to study 

 the history of the beds for its own sake. 



The Corallian rocks, as traced across the country, are separated 

 into several areas, not simply by denudation, but by their original 

 form, as we judge by a certain general similarity and connexion, under 

 the cover of minor diversities, which characterize each, and sepa- 

 rate it from the others. These areas are of very unequal mag- 

 nitude and importance; but this is just the very feature of the 

 series. They may be distinguished as follows : — 

 I. The Weymouth district. 

 II. The North- Dorset district. 



III. The North-Wiltshire and Oxfordshire range. 



IV. The Cambridge reef. 

 V. The Yorkshire basin. 



In our description of these areas we shall endeavour to remember 

 that our study is the development, physical conditions, and correla- 

 tions of the Corallian beds, and not their stratigraphy, except so far 

 as it may throw light upon the former points. 



I. The Weymouth Disteict. 



The geological structure of South Dorsetshire is well known ; and 

 it affords us three distinct opportunities of studying the Corallian 

 beds. We have first the neighbourhood of Weymouth itself, with 

 the rocks extending on the west to the Fleet near Wyke, and also 

 the two ends of the series on the northern side of the anticlinal as 

 exposed on the east at Osmington, and on the west near Abbotsury. 



The rocks in the immediate neighbourhood of Weymouth were 

 early described by Prof. Sedgwick, in the 'Annals of Philosophy' for 

 1826, when he divided the series between the harbour and Sands- 

 foot Castle into 11 groups, and remarked on the similarity of some 

 of them to the rocks at Filey Brigg : and later this same series was 

 more minutely studied by Prof. Buckland and Sir H. De-la-Beche *, 

 and divided into 33 groups. They did not, however, touch the 

 palaeontology, or assist in the correlation of the beds with those of 

 other areas. In the maps of the Geological Survey the whole is 

 simply coloured as " Coral Rag." Mr. Damon's valuable little 

 workf, however, makes this area familiar ground, and contains 

 very useful lists of fossils. More recently Dr. Waagen has called 

 the Sandsfoot -Castle beds the "Upper Calcareous Grit "J. Some 

 notice, nevertheless, even of previously described rocks, appears 

 necessary for the completion of our view of the whole deposits of 

 this area and its comparison with others. 



Speaking generalty, the Corallian beds of this area are a lenti- 

 cular mass having its greatest thickness near Weymouth — a result 



* Trans. Geol. Soc. 2nd series, vol. iv. p. 1. 



t Geology of Weymouth and the Island of Portland. 



} Versueh einer allgemeinen Classification, &C, 



