Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/114

76 76 S. V. WOOD, J TIN., AND F. W. HARMER ON THE signs of any gradual disappearance of the shells by the abstracting agency being apparent, and also that the dividing line was very irregular, the shelly crag often rising in a boss or prominence (as in sections I. and II.). The unfossiliferous layers underlying in some cases detached portions of shelly material, as in section III., also pre- sented a difficulty. In addition to these was the presence not merely of a separate and independent stratification, but the circumstance of bands of ferruginous loam at the base of the sands, sometimes, as in section II., enwrapping in an entirely unconformable way pro- minences of shelly crag. Fig. 2. /Section II, in a pit three furlongs east of Great Bealinys church. (Scale 10 feet to the inch.) a and b as in fig. 1. b Band of dark, partly indurated, ferruginous loam. Notwithstanding these difficulties, however, we are inclined to think that the view expressed by Mr. Whitaker is correct ; and we have been principally led to that conclusion by the detection of the band of pebbles shown in section I., which seems clearly to indicate that the original oblique stratification of the Crag once prevailed through these sands, and that the agent which abstracted the calcareous material was inoperative upon the pebble-band, which remained as part of the original stratification. If this view is correct, it is clear that in many, indeed in most, cases the material has been so far restratified in the process, that the present stratifica- tion of the sands is often as unconnected with the original stratifica- tion of the deposit as is cleavage or jointing in the cases of the old rocks. In saying this, however, we would not be misunderstood as suggesting that there has been a rearrangment of the whole of the original material of the Crag, because, since the originally oblique bedding of the pebble-seam remains unaltered, it is evident that the arrangement of the sand particles among which this was imbedded cannot have changed, or the position of the pebble-seam would have changed with them. It is the argillaceous and ferruginous material taken up by the percolating water which has been redeposited, so as to form, in combination, the coloured threads and bands which give rise to this apparently new stratification. It not unfrequently happens that the sands and the shelly Crag