40 TYPE AMMONITES— VI Dec. 



In regard to what has been said above (p. 29) about the dogger 

 beds in the Shotover (Grit and Fine) Sands of Shotover and the differing 

 Ammonoid faunas which they yield : there is an excellent photograph 

 of the middle exposure mentioned — the northern of the two exposures 

 in the brickyard — given in Geol. Oxford, 2nd Ed., by J. Pringle (Mem. 

 Geol. Surv., 1926), PI. iv, fig. A. It shows the different levels at which 

 the doggers he. From the lowest level displayed in this photograph 

 has come Wheatleyites fauna — better developed at the southern exposure 

 of sands in the brickyard, and still better seen at Wheatley brickyard. 

 From the middle layers, hard, bluish grit except where weathered, has 

 come the fauna of Shotoverites, Pedinatites, Keratinites, with large Pernas 

 and other lamellibranchs. 



The Hartwell Clay : Since the remarks about the Hartwell 

 Clay and its correlation were published (T.A., part 60, Oct. 1926), Dr. 

 F. L. Kitchin has reiterated a statement of his views (Lam. Upper Kimm. 

 Clay and position of Hartwell Clay ; Ann. Mag. Nat. Hist. (9) xviii, 

 Nov. 1926). His table, p. 453, adds nothing new, and makes the mistake 

 of correlating Portland Sands of Buckinghamshire (Paravirgatitan) with 

 Portland Sands of Dorset (Behemothan). In p. 454 he says : " It is 

 difficult to understand, assuming his [my] interpretation to be sound, 

 how we can account for the absence of the pallasioides-i&nna. [Hartwell 

 Clay] below these sandy beds [pectinatus] at Wheatley, Shotover, and 

 Swindon, and below the Saccocoma-honzon in Dorset. In the first 

 place, the Hartwell Clay should be above the Saccocoma-horizon ; in 

 the second place there are, at Swindon, below the pectinatus beds, a thick 

 series of sands (Lower Cemetery beds) above some feet of clay, whose 

 ammonoid faunas are quite unknown : these beds are where the Hartwell 

 Clay faunas should be sought (p. 36) ; in the third place, local absence 

 of strata is too common a phenomenon to cause any trouble. It is no 

 more difficult to imagine that the Hartwell Clay, some 20-30 feet thick 

 at Hartwell, should be quite absent from Wheatley, some 15 miles to 

 the westward, than to see that the Thame Sands, some 80 feet thick 

 at Long Crendon, separating the Lydite Bed above from Hartwell Clay 

 below, has totally disappeared at Hartwell, where Lydite Bed and 

 Hartwell Clay are in contact — Hartwell being only some 7 miles to the 

 eastward of Crendon. 



Dr. Kitchin wishes to show in his paper that the Hartwell Clay 

 and the rotundum beds are synchronous by producing an Astartid 

 (HartwelUa hartwellensis) from both ; but without showing that Astartids 

 are sufficiently restricted in range for such purpose. Considering that 

 there are abundant ammonoids both in the Hartwell Clay and in the 

 rotundum beds, and that ammonoids are known to be very restricted 

 in vertical range, it is surely reasonable to ask for isochronism of these 

 deposits to be proved by them. 



There is little to be gained in reiterating statements of correlation 

 without figuring the ammonoid evidence. I have figured such evidence 

 for my correlations of the beds concerned. Though there is still more 

 to be done, this evidence of the figures should be sufficient for judgment 

 on my conclusions. Further evidence may need to be sought at Long 

 Crendon and Brill in Buckinghamshire and at Swindon in Wiltshire, 

 but special excavations will be required. 



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