THE CAMBKIDGE GAULT AND GREENSAND. 271 



terize the base of the Upper Gault, and are not known in bed XI. 

 The fossils obtained between 30 and 40 feet down were distinctly 

 those of the Lower Gault. 



It is remarkable, however, that the Gault, taken as whole, is con- 

 siderably thicker in this neighbourhood, instead of being thinner, as 

 I should have expected ; for a few miles further west, at Burham, two 

 borings gave respectively the depths of 160 and 200 feet; but 

 perhaps the greater thickness of the Gault here was in reality the 

 very cause of the denudation ; for it might have formed a great roll 

 or bank in the Chalk sea, the top of which would naturally be ex- 

 posed to erosion. 



However this may be, there is no doubt about the relations of the 

 strata ; and these seem to continue with an absence of Upper Green- 

 sand as far westward as Westerham ; here, however, hard beds of 

 " nrestone " and "malm rock" come in below the Chalk-marl, and 

 rapidly acquire thickness and importance. Under these the upper- 

 most sandy beds of the Gault seem again to be present ; and on this 

 point I may quote the words of Mr. Godwin- Austen in a paper de- 

 scribing the phosphate-beds near Guildford*. He says, " the phos- 

 phate nodules are abundant in the Upper Greensand, but are generally 

 small in the top beds ; below comes the nrestone or malm rock 20 to 

 25 feet thick, and beneath this again other beds of bright green 

 earth, of which one portion is argillaceous ; this lower green band is 

 the Gault. The concretions of phosphate of lime are not scattered 

 throughout it, but occur in two seams — one in the argillaceous por- 

 tion, the other lower and only a little within the limits of this divi- 

 sion of the series. These two beds of phosphate nodules, as well as 

 a seam of pyrites staining the Gault of a brown colour, are remark- 

 ably persistent." 



Along the foot of the South Downs very little appears to be known 

 of the Gault and Greensand ; but at Eastbourne there is again a cliff- 

 section, of which my friend Mr. Maddock has favoured me with the 

 following particulars : — 



ft. 

 Chalk-marl, with basement-bed consisting almost entirely 



of Brachiolites labyrinthicus — 



Chloritic marl, with numerous phosphate nodules and 



fossils about 8 



Upper Greensand, soft green sands with a hard band of 



rock in the middle 26 



Upper Gault, grey sands with clay below, containing 



the usual fossils of the division 8 shown. 



In reviewing the above descriptions and sections, let me remark 

 that in three of the localities mentioned the sands of the Upper Gault 

 are present, with fossils and phosphate nodules ; while in the fourth 

 they are absent, and there conditions prevail similar to those so well 

 known at Cambridge. This fact cannot but have much weight in 

 considering the reason of such conditions. 



§ 6. Conclusions from Stratigraphical Evidence. — A fair consider- 



* See Quart. Journ. Geol. Soc. Tol. iv. p. 257. 



