GEOLOGY 



soddened clay slopes of the bounding hills, and ultimately left, on a 

 cleanly-washed surface of blue Lias clay (Northampton) a deposit of 

 coarse gravel, to the depth of 20 feet or more, in the lower parts of the 

 conical bottom of the valley. This deposit is of course a Mid-glacial 

 gravel, and not a river gravel as commonly called. It is seldom to be 

 seen because charged with water and below river level, but a very large 

 excavation was made in it at the Northampton Gas Works some years 

 back, 34 feet down to the clay, and no trace of terrestrial life, such as 

 true river gravels yield, was found. 



Valley Gravels or River Gravels 



It is quite certain the melting of the second ice sheet which ter- 

 minated the Glacial period did not produce such violent floods as the melt- 

 ing of the first, but for this reason alone they must have lasted longer in 

 the valleys then opening up. Owing to the land at first being lower than 

 now (we will say 150 feet), the earliest formed valley gravels would be 

 high up the valley and high up the sides of it after re-elevation of the dis- 

 trict ; but with the rising of the land similar deposits would be formed at 

 what would now be called lower levels, though all may have been formed at 

 approximately the same level above the sea of the time, making allowance 

 for fall in the valley. So we have high-level gravels and loiv-leve I gravels. 

 The earlier formed river terraces have mostly been obliterated by more 

 recent slipping and denudation, but the later ones are nearly everywhere 

 found as a wide fringe to the present valley, occupying positions from 

 river level to 40 or 50 feet above it. 



This river gravel consists chiefly of the contents of the previous ice- 

 cap, that is to say it is essentially the residue of a washed Boulder Clay ; 

 it contains flint and Bunter pebbles in abundance, and physically can 

 scarcely be distinguished from some of the Mid-glacial gravels. It is 

 interesting in that it contains remains of various terrestrial animals, some 

 of which do and others do not now inhabit England, and of others which 

 are extinct, together with the earliest indications of man in the shape 

 of rude flint implements, showing it to belong to the Paleolithic or 

 Older Stone age. 



The remains of terrestrial animals reported from the river gravels of 

 this county include the mammoth [Elcphas primigenius), early elephant 

 (£. antiqtii/s), rhinoceros (two species), hippopotamus, reindeer, red 

 deer, wild hog, ox and horse. In the upper part of the Nene valley 

 the remains are apparently fewer than lower down, and moreover 

 restricted to the heavier and harder parts of animals, such as 

 molars and tusks, which could survive the turbulent waters that formed 

 the gravel ; but lower down, towards Peterborough, where the valley 

 was at first under, and afterwards at the edge of the sea, Estuarine con- 

 ditions prevailed, sand largely replaced gravel, and there is a mixture of 

 marine shells, such as oysters, cockles, etc., with delicate terrestrial and 

 freshwater molluscs, as Helix, Planorbis, Limncea, etc., and other parts 

 than tusks and teeth of the larger terrestrial animals cited above. 



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