ON SOMK ANCIF.NT I.AKK REMAINS AT FELSTEAD, ETC. 35 



cutting of the new channels exposed some sections of soil varying 

 from two to ten feet in depth, and as these occuron both sides of the 

 dam, we are enabled to study the deposits of the lake and the con- 

 temporaneous deposits which formed on the other or outer side of 

 the dam. I may here mention that at the time the workmen widened 

 the old breach of the dam they found some curious im{)lements 

 which they took to be "Mill-bills," but which equally well might 

 have been " Celts." These relics are lost. 



The dam is about 150 yards long, about 35 feet broad at its base, 

 and 10 feet at its top, and is about 20 feet high at its deepest part. 

 It is made most probably of Gravel and Boulder-clay in equal layers, 

 and would hold back perhaps 10 acres of water or more. 



Of the first deposit inside the dam we cannot speak with certainty, 

 as the channel does not cut through it. At one place the brook 

 flows over very compact dark lake mud, destitute of stones, and nearly 

 so of organic remains. Traces of oyster-shells may be noticed 

 sparingly, and there are the nacreous remains of some fresh-water 

 molluscs. The corresponding level at a point higher up stream is of 

 gravel which as yet has furnished no relics. 



On the outside of the dam the original bottom is exposed in the 

 section cut by the stream. It is of Chalky Boulder Clay. Paren- 

 thetically it may be observed that Boulder Clay occupying the 

 bottom of a valley is rare. The sheet of Boulder Clay also extends up 

 the northern side of the valley slope to a considerable elevation. It is 

 necessary to bear this in mind. 



Soon after the dam was made, perhaps immediately after, a fire 

 was lit on this newly scooped out Boulder Clay, and the fragments 

 of charcoal and calcined stones resulting remain to this day. It 

 would seem that the place of this fire, occupying a depression, soon 

 became saturated with water, because in immediate contiguity to 

 these ashes is a thin layer of shell-marl. The species occurring are 

 Land-shells of various species ; among them occur Helix arbustomm 

 and Cyclostoma e/egans, both of which are now considered to be 

 locally extinct. 



The first overflow of the dam has left unmistakable evidence of 

 its work. This is a bed of rather coarse gravel of about two feet in 

 thickness. It would seem that the first overflow came from the 

 northern end of the dam, and eroded some Glacial gravel at that 

 point. It then passed down the slope of the valley in a line parallel 

 and near to the side of the dam and In id down the gravel in its 



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