Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/879

Rh PROP. J. BTTCKMAN OK THE MIDFORD SANDS. 739 It should, however, be noted that in the sands there are occasional seams of carbonate of lime, apparently derived from the decay of layers of Testacea which have been decomposed in the porous stratum. The Gloucestershire sections and the Somerset and Dorset ones agree in having a Cephalopoda-bed at the base and another high up. Our grand Cephalopoda-bed in Dorset is the equivalent of the Gry- phite-Grit on the top of Leckhampton Hill, and both are marked by a list of characteristic Ammonites, amongst which are the following : — List of Ammonites common to the Upper Cephalopoda-beds of Dorset, Somerset, and Gloucester. Ammonites Brocchii, Sow. Ammonites Humphriesianus, Sow. Sowerbii (Brownii?), Sow. Parkinsoni, Sow. concavus, Sow. subradiatus, Sow. corrugatus, Sow. lasviusculus, Sow. Now these species are common to both districts ; and be it recol- lected that as sand underlies this upper Cephalopoda -bed in Dorset, while sand underlies the lower Cephalopoda-bed in Gloucestershire, these two beds have been considered as belonging to the same horizon ; it was so thought by the late Prof. Phillips, and hence he aime:l at getting rid of the difficulty by naming these as follows: — " Midford Sands. " The last of the liassic strata, to which the inferior oolite has not quite relinquished its ancient claim, is a variable series of fine sands, deposited on the upper lias clay in such a manner as often to defy the geologist to draw a hard line between them. These sands are bluish under ground, yellowish at the surface. They are covered in many districts in the south of England by calcareous and shelly beds, "which on the first view appear naturally associated with the oolitic rocks above; but they contain many fossils which are frequent in the sands and not common in the oolites. Thus we have in general terms Inferior oolite above. Shelly calcareous bed. Fine-grained sands. Upper lias clay below. " Here, then, is a transition series of beds, which for convenience and for reasoning may be joined with either or both of the greater deposits, which, in fact, they feebty tie together"*. Now when we consider that the sands at Midford are the equi- valents of a great mass of the Inferior Oolite of Leckhampton, Hors- field, and Crickley, it will be seen that, however the name of either Oolite or Lias sands for the beds below the Gloucestershire freestones may apply, the term Midford Sands cannot apply to the equivalents of the freestone and ragstono beds of the Cotteswolds, of which these so-called Midford Sands undoubtedly are the equivalents. Hitherto we have described the beds below the so-called Cephalo-
 * Geology of Oxford and the Valley of the Thames, p. 118.