58 ME. G. W. LAMPLUGH OX THE JU>X'TIOX OF [vol. Ixxviii,. 



conditions on the north and of deeper water with strong and steady 

 currents on the south ; and it must be remembered that a distance- 

 of 2 miles at right angles to the trend of a coast-line gives ample 

 space for great A^ariation in the character of marine sediments. 



About the beds of the Grovebmy type, there is no question. la 

 their position, lithological characters, and fossil contents, they are 

 recognizable with certainty as the equivalents of the ' Mammil- 

 latus Beds ' of English and French geologists. These beds are 

 everywhere notoriously variable, and their exceptionally Avide 

 exposure in these sections affords an unusual opportunitj' for- 

 studvinsr them in detail. The beds are of aboat the same thick- 

 ness as at Folkestone, but preserve, in their well-distributed 

 nodules, a somewhat fuller, though still imperfect, record of the 

 life of the period, agi-eeing more nearly in this and other respects, 

 with their equivalents in the ]Ss"orth of France, particularly in the 

 region of the Ai'gonne. At Folkestone, the fossiliferous phos- 

 phatic nodules are almost entirel}' confined to one band, in which 

 they have been segregated into clusters,^ and the accompany- 

 ing glauconitic sandy deposits contain scarcely any fossils. At 

 Leighton, although again it is unusual to find anything preserved 

 in the glauconitic matrix, the phosphatic nodules stud the beds at 

 all levels, and contain a wider range of fossils. It is clear that the 

 phosphatic concretions have been formed in a matrix like that 

 which now surrounds them ; but they often show" traces of sub- 

 marine corrosion and wear, indicating that they have lain exj)osed 

 at times on the sea-floor. They were formed quickly enough to 

 enclose in a fresh state the organic relics which lay on the sea- 

 floor, nearly all of which have perished utterly where not thus en- 

 closed. All the circumstances imply a lengthy period of very slow 

 deposition, with bottom-currents strong enough at times to disturb 

 and winnow the sea-floor, but not strong enough to sweep away 

 the nodules. 



The resemblance of these nodules to the coquins de sable 

 occurring, sometimes segregated into a band and sometimes 

 scattered, in the Mammillatus Beds of the Argonne is remarkably 

 close; as may be judged from the following extracts from the 

 description of the French sections by Prof. C. Barrois ^ : — 



' Ces nodules, appeles coquins par les habitants du pays, ont la forme de 

 rognons arrondis, tuberculeux, ils sont compacts, noiratres, et d'une couleur 

 generalement plus foncee a I'mterieur qu'a la surface. . . . ces nodules sont 

 rarement homogenes, ils sont penetres et soiivent reconverts a la sui'face de 



^os grains de quartz, de glauconie Les ouTriers distinguent parfaite- 



ment ces nodules qu'ils appellent coquins de sable, des nodules de la gaize 

 qu'ils appellent coquins riches' : — 



And it may be remarked here that at Leighton a corresponding- 



^ See my notes on the Copt Point (Folkestone) section in Jukes-Bro"vvne"s. 

 pre-vioiTsly cited memoir on the Gault, &c. (Mem. Geol. Surr.) p. 73. 



" ' Sur le Terrain Cretace des Ardennes & des Regions voisines ' Ann. Soc^ 

 Geol. Nord, vol. v (1878) p. 277. 



