A. 8. Lucas — The Heaclon Beck of the Isle of Wight. 99 



stratigraphically, because they are conspicuous and resist denudation 

 better than the associated sands and marls. Thus the great Headon 

 Limestone from its lenticular contour cannot serve as a well-defined 

 hoi-izon save in the hill itself, where it is continuous. In Colwell 

 Bay, if we recognize its coincidence with the 1ft. 4in. buff Limnea 

 Limestone, we must do so from the correspondences of superior and 

 inferior beds ; for this Colwell Bay Limestone might be another 

 similar intercalation. 



We think the stratigraphical evidence alone yields very clear 

 results. In Headon Hill we can obtain a standard section reaching 

 from the top of undoubted Headon Hill Sands to the base of un- 

 doubted Bembridge Limestone. Such a standard section is deduced 

 by combining vertical sections made at various points in the Hill. 

 There is no break in the strata. The vertical section of the Survey 

 near Heatherwood Point includes the Bembridge Limestone, the 

 Osborne Marls, the Osborne Limestone, the Great Upper Headon 

 Limestone, the brackish-marine, and the Lower Headon Limestone 

 with a few beds below. It practically agrees with that of Prof. 

 Blake taken about the middle of the W. face of the Hill. Near 

 the S.W. corner, again, a vertical section includes the Osborne 

 Limestone, the Great Limestone, the brackish-marine, the Lower 

 Headon Limestone, and the Headon Hill Sands. As no vertical 

 section at this point has been published, though details obtained 

 fi'om it are implied in the horizontal section D of the Survey, 

 we give a few measurements of the height above sea-level of critical 

 points, that of the Sands fixing the spot at which the section was 

 observed, somewhat to the N. of Alum Bay Chine. 



Top of Headon Hill Sands 24^ ft. 



Base of Lower Headon Limestone (6ft. thick) 106^ ft. 



Base of Great Planorbis Limestone 144 g ft. 



Base of Osborne Limestone 184| ft. 



The Lower Headon Beds were so obscured by the " mud glaciers " 

 that we did not venture on a detailed record. Of the brackish-marine 

 we preserved the following memorandum. Below the freshwater 

 Sands beneath the Great Limestone we found, as we worked down, 



' ' Blue clay mth Cerithia {coneaviim and ventricosum) 4ft. Gin. 



Ferruginous Sand 2ft. Sin. 



Blue clay 7ft. Sin. 



An oyster bed 2ft. 6in. 



Blue clay -with G. coneavum 8ft. 



Brown clay with Lignite 1ft. Sin. 



A zone of Cyrena obuvata 1ft. 



Ferruginous Sands 1ft. 



A zone of Cyrena obovata 1ft. 



Lignite S or 4 in. 



Blue clay 2ft." 



We found fragments of Cytherea incrassata in the clays of the middle 

 zones, which with Fusiis labiatiis, Ostrcea velata, Natica depressa, etc., 

 marked off a larger marine series below from a smaller brackish 

 series with the Cerithia, etc., above. We have no record of fossils 

 in our note from the lowest clay, while the Lignite and Cyrena beds 



