Mr Lake, Shell-deposits fornied by the flood of January/, 1918 157 



Shell-deposits formed by the flood of January, 1918. B}- Philip 

 Lake, M.A., St John's College. 



[Read 18 February 1918.] 



The heavy snow of the third week in January 1918 was followed 

 by a very rapid thaw and a considerable fall of rain, and the Cam, 

 in consequence, rose to an exceptional height. In the neighbour- 

 hood of Cambridge the floods were the most extensive of recent 

 years, the water reaching its highest level on Sunday, Jan. 20. 



The traces of the flood remained visible for several weeks, its 

 limits being marked in most places by straws, twigs, silt, etc., with 

 a sprinkling of land and fresh-water shells. But below the town, 

 near the railway-bridge, the shells were so abundant as to form a 

 remarkable deposit, which seems to deserve a special record. It 

 was not till the 25th Jan. that I saw it, and the following notes 

 are drawn up from the observations made on that day and on two 

 or three subsequent visits. 



The deposit lay partly upon the tow-path and partly in the 

 shallow ditch on the iimer side of the path, and it extended with 

 little interruption from the immediate neighbourhood of the 'Pike 

 and Eel ' to a point about 850 yards below the railway-bridge, a 

 total distance of approximately 850 yards. Occasional patches 

 occurred still farther down, and scattered shells even as far as 

 Ditton Corner. Beyond Ditton the tow-path was in several places 

 covered with a thick layer of silt, but I saw no more shells until 

 within sight of the lock at Baitsbite. 



The deposit was somewhat irregular and it was difficult to form 

 an estimate of its average width, but this can hardly have been 

 less than a foot, and was probably much more. 



Above the railway-bridge the shells were mixed with silt, 

 especially in the ditch on the inner side of the path ; but even 

 here the proportion of shells was large, and in places they formed 

 the bulk of the deposit. Below the railway-bridge the deposit was 

 free from silt and consisted entirely of shells. In the shallow 

 hollows formed by the irregularities of the surface, it was often an 

 inch or two deep, so that it was possible to scoop up the shells by 

 the handful. Owing to its colour it showed conspicuously as light 

 streaks upon the slightly darker path. 



By far the greater part of the deposit consisted of Limnaea, 

 L. stagnalis and L. peregra being the most abundant species ; but 

 other fresh-water shells also occurred and land-snails were by no 



