138 Correspondence — Rev. 0. Fisher. 



It may be well to conclude by summing up briefly the grounds for 

 coming to an arcbasological conclusion at Blackbeatb. 



They are : — 1st. The great improbability of any cavity in the 

 chalk under Blackheath in consequence of the very small quantity 

 of chalk there above the permanent water-level. This point was 

 especially dwelt upon by Prof Prestwich in his letter to Mr. J. K. 

 Laughton, Chairman of the Blackheath Subsidence Committee. 



2ndl3r. The additional improbability of any cavitj^ in consequence 

 of the presence of the clayey beds (10 or 12 ft.) of the Woolwich 

 Series below the Blackheath pebble beds which form the surface. 



Lastly. We were more fortunate at Blackheath than Messrs. 

 Fisher and Rutley at Lexden, not only in having much more 

 geological evidence, but also an amount of archaeological evidence, 

 in the pits popularly known as '' Danes' Holes," which would suffice 

 to turn the scale against a geological explanation, even were the facts 

 against one much less weighty than they are. 



28, Ceooms Hill, Greenwich, T. V. HoLMES. 



Jan. lOih, 1882. 



ON THE STRATA OF COLWELL BAY, . HEADON HILL, AND 

 HORDWELL CLIFF. 



Sir, — I have lately read Prof. Blake's article on the strata of 

 Colwell Bay and Headon Hill, published in the Proceedings of the 

 Geologists' Association for October, 1881. Since I took a somewhat 

 (I fear) over-prominent part in the discussion of Messrs. Keeping 

 and Tawney's paper to which it refers, I should wish to say a few 

 words on the subject. 



I cannot think it can be fairly asserted that Prof. Judd's views 

 " wei'e attacked by Messrs. Tawney and Keeping in a spirit unjusti- 

 fiable in any scientific controversy." When we recollect that one 

 of the authors was born in the Isle of Wight, and spent the best 

 years of his life in professional work, chiefly in exploring and 

 collecting from the Eocene beds of the district, some little amount 

 of warmth was justifiable in defending, what were his own well- 

 matured views, as well as those of the Surveyors, against an attack, 

 which, however learned, was apparently based upon work in the 

 library and museum. 



Palfeontological evidence is a powerful assistant to stratigraphy, 

 but it must yield precedence to results clearly made out in the field. 

 My own investigation of the section certainly supports the views 

 of the Surveyors, as reasserted by Messrs. Keeping and Tawney. 

 Indeed, Mr. Blake appears to me to feel a difficulty in avoiding the 

 same conclusion. ' But it is remarkable that he does not seem to 

 have applied my crucial test, referred to in Messrs. Keeping and 

 Tawney's paper, of searching for (and finding) the " Venus " bed 

 in the Totland's brick-field, at the part where, though continuous 

 inland, it has been denuded off the cliff, between Widdick and 

 Weston Chines. 



It is my own opinion that the relations of this somewhat com- 

 plicated series, in the Isle of Wight, would be made clearer to 



