198 MR. G. W. LAMPLTJGH ON THE SPEET02ST SERIES [May 1 896, 



or sparsely scattered throughout the series ; they contain certain 

 fossils proper to the bed in which they occur ; and their eroded 

 surfaces show less appearance of rolling than of corrosion from the 

 attack of various destructive organisms inhabiting the sea-floor^ 

 whose activity is similarly manifest on the undoubtedly indigenous 

 fossils of the deposits. 



The subject thus raised has broad bearings, and if my view be 

 correct there are many localities other than those now in question 

 where a revision of the evidence for the derivative character of the 

 ' phosphate-stones ' is desirable. I am satisfied, for instance, from 

 a recent examination at Hunstanton of the mode of occurrence 

 of Hoplites Deshayesii and other fossils thus preserved towards the 

 base of the Carstone, that these are proper to the deposit and not 

 derivative; 1 and a study of the literature relating to the ( phosphate- 

 beds ' at Potton, Wicken, Upware. etc., 2 shows that most of the 

 investigators of these localities have found it necessary to allow that 

 some at any rate of the nodular material is not older than the bed 

 in which it occurs. 



It is not my purpose, however, to pursue the wider question on 

 this occasion, 3 and I shall content myself for the present by restating 

 my conviction, based on a careful study of the various types of 

 nodules and concretions marking the different horizons of the 

 Speeton Clay, that some of these, including the dark phosphatic 

 stones, have gathered in the mud of the sea-bottom, and have formed 

 hard masses before the accumulation of the overlying strata, 4 and 

 that the comparative rarity or abundance of concretions of this type 

 affords a rough measure of the rate of deposition of the enclosing 

 material. 



The investigations of the Challenger expedition 5 have taught 

 us that the formation of nodules both of phosphate and manganese 

 is still taking place in areas of slow deposition beneath our existing 

 oceans, and from the description given of the former they appear to 

 agree remarkably in shape, size, and general characters with those 

 under consideration. It is true that the conditions are in many 

 respects not analogous, but the phenomena are probably, none the 

 less, closely illustrative of those of our Jurassic and Cretaceous seas, 

 wherein the marine sediments seem to have been characterized by 



1 See reference to these in W. Keeping's 'The Fossils of Upware and 

 Brickhill,' Cambridge, 1883, p. 57. 



2 Among other works see J. J. H. Teall, ' The Potton and Wicken Phosphatic 

 Deposits ' (Cambridge, 1875) ; W. J. Sollas, Quart. Journ. Geol. Soc. vol. xxix. 

 1873, p. 76 ; W. Keeping, op. jam cit. p. 17. See also the discussion between 

 Walker. J. F. (Ann. & Mag. Nat. Hist. ser. 3, vol. xviii. 1866, pp. 31 & 381, and 

 xx. p. 118), and H.G. Seeley (Ann. & Mag. Nar,. Hist. ser. 3, vol. xviii. p. Ill, and 

 xx. p. 23) ; and 0. Fisher, Quart. Journ. Geol. Soc. vol. xxix. (1873) p. 52. 



3 For an excellent summary of our knowledge on this subject, with extensive 

 biblioeraphv. see P.. A. F. Penrose, Jun., 'Nature and Origin of Deposits of 

 Phosphate of Lime,' Bull. U.S. Geol. Surv. vol. vii. no. 46 (1888), p. 475. 



4 At the meeting of the Geol. Soc. previous to that at which this paper was 

 read, Messrs. A. J. Jukes-Browne and Hill put forward a very similar explana- 

 tion for the phosphatized fossils and nodules of the ' Cenomanien.' 



5 Challenger Keports, 'Deep-Sea Deposits' (London, 1891), p. 391. 



