370 ME. T. V. HOLMES ON SECTIONS BETWEEN 



wondered at the extraordinary diversity in the opinions which have 

 been expressed from time to time as to the age and affinities of these 

 deposits. Two influences seem to have been chiefly instrumental in 

 producing this variety of view. In some cases the stratigraphical 

 evidence, considered as a whole, has been neglected or greatly under- 

 valued, while that derived from some special class of fossils from 

 one of the few f ossiliferous beds has been considerably over-estimated. 

 In others the presence of signs of ice-action in some form, a thing 

 common at various horizons in these deposits, has led to the suppo- 

 sition that these indications imply that the beds showing them date 

 from the Glacial Period. Peeling that ice has been a geological 

 agency from the earliest times, and that it did not cease to be one at 

 the close of the Glacial Period, I have lately taken more than one 

 opportunity of protesting against an assumption which seems to me 

 based on insufficient grounds.^ Por where could we expect to find 

 signs of the action of river-ice if not in the drifts of the Thames 

 Valley, formed when the land was higher than it now is and the 

 climate consequently more severe ? The question, therefore, whether 

 certain beds should be classed as of, or later than, the Glacial Period 

 in this locality, depends simply on their stratigraphical position as 

 regards the Boulder Clay. In this case it seems evident that there 

 is a strong natural presumption that the Thames Yalley deposits at 

 higher levels are older than those at lower elevations, the highest 

 terrace being the oldest— a presumption which, in the absence of 

 stratigraphical evidence to the contrary, becomes almost a certainty. 

 Previous to this discovery of Boulder Clny in connexion with the 

 oldest terrace of Thames Yalley Gravel I had always felt that Mr. 

 Whitaker's conclusion that the Thames Yalley deposits are (locally) 

 post-Glacial, or newer than the local Boulder Clay, was, in all pro- 

 bability, correct, and the truth of this view has now been demon- 

 strated by the section in the cutting at Hornchurch. 



Discussion. 



The President said that geologists were much indebted to Mr. 

 Holmes for drawing attention to this interesting section before it 

 was too late. Amongst the many points arising from the discovery 

 of Boulder Clay at less than 100 feet above Ordnance datum was 

 one as to the probability of the pre-Glacial age of the Thames Yalley 

 system. 



Mr. H. B. WoonwAED, who had seen the section at Hornchurch 

 under the guidance of Mr. Holmes, remarked that it afforded a 

 better exposure of Boulder Clay than he had elsewhere seen in 

 Essex during two years' work on the Geological Survey. Attention 

 had previously been drawn to contortions that may be seen in ex- 

 posed portions of the Thames Yalley deposits, as at Grays, and these 

 had been attributed to Glacial action, while some of these superficial 



' Proc. Geol. Assoc. toI. xi. (1890) p. 334 ; ' Essex Naturalist,' vol. iv. (1890) 



