Bev. 0. Fisher — The Coprolite Pits of Cambridgeshire. 67 



tion and the superficial deposits in them to some other cause than 

 the river. 



There is, therefore, much more reason to consider the trail as due 

 to rain-wash. If any bare surface of ground is subjected for some 

 length of time to the action of rain, it soon begins to exhibit in minia- 

 ture a contour not unlike that of the ordinary landscape. This 

 seems to prove that rain is capable of moulding the surface to such 

 inclinations as usually occur. Moreover, the mixtures of clay, sand, 

 and gravel, which are accumulated in some spots by torrents of rain- 

 water, even when the torrents are quite small, exhibit a structure 

 not unlike that of trail. 



But I have already, in former papers on this subject, brought 

 together arguments for doubting whether rain can have produced all 

 the observed effects, and I do not wish on the present occasion to 

 reiterate them. Nevertheless, I am free to acknowledge that I have 

 frequently been greatly staggered in my conclusions, and have been 

 led to doubt whether after all rain has not been the agent in pro- 

 ducing the trail and moulding the landscape which it envelopes. 

 But on consideration I have always reverted to the contrary opinion. 



I will now mention some of my observations in coprolite pits 

 which have confirmed me in believing^ rain incompetent to explain 

 some of the phenomena. 



In the first place, if rain be the agent, why should the trail be 

 separated by a surface of demarcation from the superficial soil or 

 warp ? The surface soil has undoubtedly been formed under the 

 action of rain, and if the trail were also so formed, the two ought 

 not to differ in character; or, at the least, they ought to graduate 

 into each other. And wherefore should the demarcation between 

 the two be the limit below which organic remains do not descend ? 

 These facts prove, at any rate, that if rain was the agent which pro- 

 duced the trail, it must have done so under conditions certainly 

 differing from those which exist at present. 



The occurrence of large stones in the trail is also to my mind a 

 difficulty. They are found hereabouts most abundantly under the 

 hills which are capped with Boulder-clay. There is no doubt 

 where they come from. But if the clay has been washed away by 

 rain, ought not all the large stones to be left behind, and not a few 

 here and there, say one or two cart-loads to the acre ? 



Again, if rain-wash be the source of the trail, it seems that it 

 ought to have been washed down by the shortest route from higher 

 ground. But I have found coprolites in it where there is no outcrop 

 of the Greensand above, but where they must have come by a 

 route parallel to the direction of the hill ; the outcrop at the locality 

 being at a lower level than the place where they occur, though they 

 crop out at a higher level further up the valley. 



But the most remarkable phenomenon, and indeed that which 

 has led me to offer these remarks, is the evidence of lateral 

 thrust which I have noticed, and which in at least two instances has 

 produced a reduplication of the coprolite bed. In one case the ac- 

 companying section appeared in the face of the pit. The locality 



