﻿1850.] 



TRIMMER ON THE ERRATICS OF NORFOLK. 



23 



the outcrop of the secondary strata on the west, the declivity of the 

 surface on which the erratic tertiaries rested has been greater, and 

 their denudation more complete. 



Patches of boulder clay occur at the commencement of the descent 

 from the summit level to the estuary of the Wash ; but in general it 

 has been wholly removed on the declivity, and the reconstructed ma- 

 terials of the upper erratics have been brought down to lower levels, 

 during the process of upheaval, where they are in immediate contact 

 with the secondary strata. Till, in the form of blue clay containing 

 fragmentary chalk, has been found underlying the alluvial deposits 

 at Lynn and Denver Sluice. 



12. At an elevation of about 30 feet above the level of the Wash 

 we have the older estuary deposit of the valley of the Nar, described 

 some years since by Mr. Rose*, with its marine shells all of existing 

 species (though not the same group as that of the marine alluvium of 

 the marshes and of the existing estuary) associated with bones of the 

 horse, elephant, and rhinoceros. I have the authority of Mr. Rose 

 for stating, that while he still adheres to the statement in his paper, 

 that the Nar clay is not anywhere covered by deposits containing 

 blocks transported from a distance, he has found situations where it 

 is overspread with loam and gravel, containing flints of such a size 

 as to indicate considerable force in the currents which transported 

 them. 



13. In the neighbouring smaller valley of Gaytonthorpe, at a some- 

 what greater elevation, are some deposits of which a detailed descrip- 

 tion will be given in the sequel. The most remarkable feature of 

 these deposits is, that, amidst a general absence of organic remains, 

 one of the sections exhibits freshwater strata with mammalian teeth, 

 resting on a variety of the boulder clay ; and that pipes and furrows 

 have been formed in the freshwater deposits, similar to those in the 

 chalk which have so long attracted the attention of geologists. 



14. In other communications to the Society, I have assigned rea- 

 sons for ascribing these pipes and the furrows of which they form the 

 termination to the mechanical action of water, before the matter fill- 

 ing them was deposited. This action appears to have been in opera- 

 tion from the commencement of the eocene to the close of the erratic 

 tertiary period. In Kent, many of the pipes and furrows in the 

 chalk are filled with eocene sand. Those in the tilted chalk of Alum 

 Bay are also filled with eocene sand ; and they have the whole argil- 

 laceous mass of the mottled and London clays above them, — an im- 

 portant fact in favour of the origin which I assign to the cavities. 



Near Norwich they are filled with mammalian crag. In other 

 parts of Norfolk they are filled sometimes with that, sometimes with 

 the loamy deposit which constitutes the soil, and which I call the 

 Warp of the drift, or erratic Warp. I have sections exhibiting the two 

 classes of phenomena in the same pit. The last fills similar cavities 

 in whatever beds have been exposed by denudation, so as to constitute 

 the subsoil, whether they be beds of transported and reconstructed 

 chalk in the upper erratics, or the boulder clay of the lower erratics, 

 * London and Edinburgh Phil. Mag. 1836, vol. vii. 



