MR. T. M. KEADE AN ESTIMATE OF POST-GLACIAL TIME. 



291 



22. An Estimate of Post-Glacial Time. By T. Mellard Reade, 

 Esq., C.E., F.G.S., F.R.I.B.A. (Head February 29, 1888.) 



Of late several attempts have been made to show that the close of 

 the Glacial period was very recent*. 



Having personally devoted considerable attention to what is 

 called Post-glacial or " su])erficial " geology, I am much struck 

 with the imperfect knowledge with which the question of Post- 

 glacial time is frequently approached. 



The writers seem to be unaware of, or to insufficiently appreciate, 

 the grand sequence of events recorded in the deposits on the Lan- 

 cashire and Cheshire coasts which have taken place since the snow 

 and ice of the Glacial period disappeared f. 



On the borders of the coast-line between the Dee, the Mersey, and 

 the E,ibble, the student who cares to pursue the subject can do so 

 with great advantage. But through the horizontality of the deposits, 

 and their general low level, none occurring above the level of the 

 25 feet Ordnance datum and all reaching down to below the level of 

 the lowest spring-tides, the study has to be pursued through the 

 medium of excavations and borings. This I have done in observa- 

 tions extending over many years, and I now propose to show their 

 bearing upon the absorbing question of recent geological time. 



Denudation of the Loiu-Level Marine Boulder-clay. 



The whole of the country to which these notes specially refer was 

 formerly entirely covered with a mantle of Low-level marine Boulder- 

 clay and sands. These I have described at length in several 

 papers J. 



That the valleys of the Dee, Mersey, and Kibble were at one time 

 filled with Low-level marine Boulder-clay, we have, I think,in- 

 dubitable evidence. The ancient or Pre-giacial course of the Mersey 

 was, as I have shown, under the site of the town of Widnes in Lan- 

 cashire, and, as numerous borings have disclosed, it is now, with the 

 exception of some superficial deposits of estuarine mud, entirely 

 filled with Low-level marine Boulder-clay and sands. There is 

 strong reason to believe that even here a considerable amount of 

 Boulder-clay was removed before the deposit of the recent silt ; but, 



* Professor Prestwich estimates that the final melting away of the ice of the 

 Q-lacial period took place within from 8000 to 10,000 years of the present 

 time (Q. J. Gr. S. vol. xhii. 1887, p. 407). Mr. Mackintosh estimated it at not 

 more than 6000 years (see Geol. Mag. 1883, p. 189 and pp. 191, 192). 



t Professor James Geikie, in ' Pre-historic Europe,' is one of the few who 

 appear to have made themselves acquainted with the remarkable and important 

 changes it is attempted in this paper to explain. 



I " Drift beds of the North-west of England," Q. J. G. S., part 1, 1874, 

 part 2, 1883. See also C. E. De Ranee, Q. J. G. S. vol. xxvi. p. 657 ; ' Memoirs 

 of the Geological Survey,' &c. ; G. H. Morton, ' Geology of the Neighbourhood 

 of Liverpool ; ' and various papers by J). Mackintosh, Robert Eostock, Dr. 

 Ricketts, and several local archseologists and geologists. 



