t)6 Rev. 0. Fisher— The Coprolite Pits of Cambridgeshire. 



Trimmer, "Warp."! ^ti this district it is unusually full of land-shells 

 of recent species. Nevertheless, the assemblage is not exactly what 

 one meets with living on the spot. The most common Helix of the 

 warp is H. arhustorim. This species occurs alive in the neighbour- 

 hood, but it can scarcely be called common. Jlelix nemoralis is 

 common in the warp and also alive. Helix aspersa is by no 

 means common in the wai-p, but it is common alive. Cydostoma 

 elegans is very common in the warp, but I have not seen it alive in 

 this_ neighbourhood. It is exceedingly likely that drainage and 

 cultivation may have been sufficient to have wrought these changes. 

 At the base of the warp I have found an oyster-shell, which looks 

 as if it had been broken at the edge to get it open. 



Below the warp we have what the workmen term " mixed clay." 

 This is sometimes little else than disturbed clunch or "white clay." 

 But in other places it contains patches of clayey gravel and sand. 

 Sometimes the gravel contains so many phosphatic nodules, that it 

 is extracted and picked over for them. Among its contents are 

 pebbles of hard rocks, generally well rounded. Sometimes these 

 attain a considerable size — a foot or more in diameter. This deposit 

 is often closely compacted, and the workmen will describe it as 

 "proper hard old stuff." It is what I have elsewhere called " trail." 



Here, as elsewhere where I have examined it, this " trail " con- 

 tains no organic fossils of its own. Although in this neighbourhood 

 shells are abundant in the warp, yet they nowhere, that I have seen, 

 descend into the trail. It has the character of being a mixture of 

 the deposits of the immediate neighbourhood, but it is not strati- 

 fied. The matrix of white clay, forming its bulk, is derived from 

 the lower chalk or clunch. The flints are similar to those of the 

 gravels of the neighbourhood, and probably are derived from the 

 Boulder- clay. The pebbles and larger stones are clearly from the 

 same source ; and the phosphatic nodules must have come from 

 the outcrop of the Greensand. The question then is. What agent 

 has brought these materials together as we see them ? 



The agencies of rivers and of rain have a prescribed right to be 

 first considered. 



But when we compare the deposit in question with an admitted river- 

 gravel, like the neighbouring one of Barnwell,the difference of character 

 is at once apparent. Moreover, we meet with the trail in places where 

 rivers have never run, as in the bottoms of dry valleys ; for instance, 

 in a coprolite pit now in work below the limekiln at Eversden. It 

 is conceivable that a river, now running at the bottom of a valley, 

 may formerly have meandered over every portion of that valley 

 included within its main features, and, while at work for ages in 

 excavating the valley, may have left traces of its former wanderings. 

 But it is not conceivable that it can have departed from the main 

 valley, so as to have excavated the tributary valleys which descend 

 into it from among the hills. Consequently, when we find no traces 

 of streams in these tributary valleys, we must attribute their forma- 



^ See the author's paper on the "Warp" of Mr. Trimmer. Journ, Geol. See, 

 vol. xxii., p. 553. 



