500 Dr. A. Irving — The TJiames High-level Plateau Gravels. 



a vertical face of forty to fifty feet. The data we possess in the 

 well-sections at Elsenham and Bishop's Stortford show a gradient 

 sloping to the north of less than one degree between those two 

 places, a distance of about five miles ; the presumed reversal of 

 drainage of the ancient Cam Valley is therefore comparatively 

 a small matter. The present head-waters of the Cam and the 

 Stort have doubtless been determined by later developments in 

 the configuration of the country.^ The absence of all traces of 

 Tertiary marine deposits north of the Mercian Chalk escarpment 

 furnishes evidence of the continental elevation of north-western 

 Europe during Miocene time, as mapped by Professor Zittel in his 

 work "Aus der Urzeit." - But the physiographical agencies of 

 nature were not suspended ; and rivers gathering their head-waters 

 from a much higher gathering-ground to the north-west than exists 

 to-day, with contours of the land over the Mercian area furnishing 

 gradients sufficient to keep their middle courses pretty free from 

 detritus, could not fail to do their work in laying down extensive 

 stretches of shingle on the northern slopes of the ancient Tiiames 

 Valley, as we see it done in modern times by the floods of the 

 Alpine rivers which debouch upon the plains of Bavaria in their 

 course to join the upper Danube. 



Taking all the facts together, and taking into account the further 

 fact that observations of them b}^ the present writer for the la^t 

 ten years and by other observers has failed to detect any signs of 

 glaciation in these stratified gravels, even on the rolled sarsen 

 blocks included in them, it seems impossible to regard them by 

 any stretch of scientific imagination as ' interglacial.' It will lie 

 seen that the author's work has proceeded on lines parallel with 

 that of Dr. A. E. Salter and Mr. Osborne White, and leads to 

 similar results.^ 



The difierential earth-movements, which culminated in the Miocene 

 continental elevation, may be traced back even to Eocene time by 

 the abundant evidence that we have of the attenuation, as we work 

 northwards, of the Middle and Lower Bagshot strata. High-level 

 stratified gravels of a type differing from those described here are 

 found, as we get away from the ancient transverse lines of drainage, 

 composed chiefly of redistributed pebbles and sand of the Bagshot 

 beds, of the quondam extension of which northwards we have 

 evidence in a considerable outlier near Sudbury in Suffolk ; but 

 with these the present communication is not intended to deal. 



This short paper suggested itself as an addendum to the admirable 

 lecture by Dr. J. E. Marr, F.R.S., on the Geology of Cambridgeshire 

 at the meeting of the British Association at Cambridge, dealing, as 

 it does, with a district only a few miles removed from the county 

 boundary, physiographical relations being more important to 

 geologists than such artificial limitations. 



^ Fuller details are given by the present writer in a paper read before the 

 Geologists' Association in 1897 and published in its Proceedings, vol. xv, Feb., 1898.- 



2 Published by R. Oldenbourg, of Munich. 



3 See Proc. Geol. Assoc, vol. xiv, Aug., 1896 ; vol. xv, Aug., 1897. 



