566 E. B. TAWNEY AND H. KEEPING ON THE 



31. On the Section at Hoed well Cliffs, from the top of the Lower 

 Headon to the base of the Upper Bagshot Sands. By the late 

 E. B. Tawnet, Esq., M.A., and H. Keeping, Esq., of the Wood- 

 wardian Museum. (Bead June 20, 1883.) 



(Communicated by the Rev. Osmond Fisher, M.A., F.G.S.) 



The Hordwell cliffs have been more or less cursorily examined by 

 "Webster, Lyell, and Searles Wood, and they were described some 

 time ago by Dr. T. Wright *. Nevertheless the beds do not seem 

 to be so well known to geologists as the interest of their fauna 

 demands. The cause may perhaps be that observers have of late 

 years failed to find many of the extinct Ruminants which in former 

 times were the especial feature of the freshwater beds at Hordwell. 

 The description of these deposits by the late Marchioness of Has- 

 tings f contains the best information concerning the exact beds in 

 which the vertebrate remains were found. 



Last autumn we measured the section bed by bed, and the results 

 are here laid down (p. 567). We have adopted the graphical 

 method as an aid, because it alone enables an observer to identify 

 with facility and without loss of time any bed mentioned in the 

 letterpress, and to compare it with the exposure in the cliff. The 

 cliffs in no one spot offer an escarpment where the beds are so 

 accessible that they could be measured vertically from base to 

 summit. Our method has therefore been to measure as much as 

 could be conveniently effected at one place, and then move the 

 position of observation horizontally. Of course, owing to variation 

 in the thickness of beds when followed horizontally, any pretension 

 to minute accuracy is altogether precluded. Absolute accuracy is 

 not feasible in geological sections, nor is it necessary. If the measure- 

 ments give approximate results for the whole thickness, and preserve 

 roughly the comparative proportions between the individual beds, 

 that will usually be sufficient. It is certainly so here, where there 

 is no great change in the fauna to record. It was desirable, however, 

 to obtain the details as precisely as possible, because our object was 

 to study the distribution of the fossils, the lithological changes being 

 altogether subordinate to this end. The present table will, we hope, 

 serve as an aid, not only to our description but to the valuable work 

 recorded by the Marchioness of Hastings. 



We have affixed numbers to the different beds, in order that they 

 may be found at once in the letterpress description, which contains 

 such details as there was no room for in the section. The limits 

 between the beds are of course arbitrary. Probably no two persons 

 working separately would select exactly the same divisions, or group 

 the smaller alternations of sediments in exactly the same way. 



We have collated the beds in the Marchioness's description with 

 our own, and quote largely from her work, as it has never been 



* Proc. Cotteswold Club, vol. i. pp. 120-130, and Ann. Nat. Hist. ser. 2, vol. 

 vii. pp. 433-446. 



t Bull. Soc. Geol. France, ser. 2, torn. ix. pp. 141-203 (1852). 



