344 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 5, 



I place the Orton gravel on the parallel of the Nar clay and the 

 mammaliferous deposits of the Thames Valley, which I refer to that 

 portion of the Pleistocene epoch which I have called* the second 

 stationary, or second elephantine period, and which I have described 

 as intervening between the elevation of the erratic tertiaries and the 

 distribution of the Warp-drift over their denuded surface. 



In the Nar clay the shells are wholly marine, although it is pro- 

 bable that it terminates, on the east, in freshwater deposits similar 

 to those of the parallel valley of Gaytonthorpef . In the ancient 

 wide-spread allu-vium of the Thames the shells are exclusively those 

 of the land and fresh water. The Orton gravel is a fluvio-marine 

 deposit. 



These facts accord with the sketch-map which accompanied the 

 paper above-mentioned {op. cit. vol. ix. pi. 13, map No. 4.), illustra- 

 ting the distribution of land and water on the eastern side of England, 

 during the second stationary, or second elephantine period. 



In the Valleys of the Nene and Nar we have the elevated coast- 

 line of ramifications from a bay which extended more to the west 

 than the present estuary of the Wash. In the old alluvium of the 

 Thames, on the other hand, we have evidence of the eastern exten- 

 sion of land drained by a river of such volume, that there is no diffi- 

 culty in supposing it to have extended sufficiently to the east to 

 have been a tributary of the Rhine ;J. 



The foundation-rock of the Orton Estate is Oxford clay, with 

 beds of impure limestone on its western side ; but, from the imperfect 

 sections and the rapidity of my examination, I have not yet been 

 able to satisfy myself whether they belong to the lower part of the 

 Oxford clay or the upper part of the Great Oolite. 



The superficial deposits with which these strata are extensively 

 covered, are, taking them in the order of their antiquity, 



1. The Boulder-clay of the Lower Erratics. 



2. The Orton Gravel, reconstructed from erratic materials. 



3. The Warp-drift. 



I saw nowhere on the estate, or in its vicinity, any gravel of the 

 upper erratics, in its normal condition, that is, resting on boulder- 

 clay, or resting on other rocks at higher levels than that clay. 



The warp-drift on the Oxford clay is, in many parts of the estate, 

 more than 4 feet deep ; and, though on that clay it partakes much 

 of the nature of that bed, it contains extraneous fragments to such a 

 depth, that, except at a section aiforded by a brick-field, I could not 

 satisfy myself that I had seen it in its native state. Even there, 

 beneath a brown clay-loam, 3 or 4 feet deep and containing de- 

 tritus not derived from the subjacent stratum, there is a blue clay, 

 containing, to the depth of about 7 feet, decayed roots and other 

 vegetable matter, which not only extend through it vertically, but 

 are interstratified with it in such a manner as to cause suspicion that 

 the clay has been reconstructed to that depth. Without further 



* Quart. Journ. Geol. Soc. vol. ix. p. 295. f Op. cit. vol. \\i. p. 26. 



X Loc. cit. and Quart. Journ. Geol. Soc. vol. vii. pi. 7. 



