15 



Since this paper was written it is more generally conceded that 

 chalk flints have heen formed subsequently to the deposition of the 

 chalk by infiltration of soluble silica and re-combination with chalk. 

 Mr. Prestwich long ago pointed out in the Thanet Sands long vermiform 

 impressions of casts, apparently of fuci, and that the palceontological 

 condition of the Thanet Beds points to littoral rather than to deep sea 

 origin; and, also, it is suggested, that the pebble beds that occur so largely 

 in the upper beds point to a large and deep wearing away of the chalk 

 about this period. 



The author quoted Mr. J. S. G-ardner with reference to the conform- 

 ability of the Thanet Beds to the chalk, where he writes : — 



" The Thanet Sands are as little conformable and had as little to do 

 with the chalk, as the Goodwin Sands." — " The Thanet bed further 

 shows that it must have been deposited within the depth to which 

 the Laminarian Zone extends : and the imbedded sea-weed may well 

 account for the peculiar character of the blackish green mud-like 

 sediment in which the green-coated flints are imbedded." 

 Prestwich, likewise, was quoted in reference to this bed : — 



" That in burning it gives off ammonia in abundance, an evidence, he 

 considered, of the presence of animal matter," and adds "This 

 bottom bed might, of course, belong to a very much older period 

 than the rest of the Thanet beds." 



It was noted that closely associated with these green-coated flints, 

 and in variable thickness, a bed of yellowish-drab sandy clay was met 

 with, and although generally classed with the Thanet bed above, (differing 

 but little in lithological characters from the immediately overlying sands) 

 nevertheless, possesses some peculiar chaiactez'8 of its own, which may 

 entitle it to rank as a separate formation, being destitute of any fossils by 

 which it may be classed with the beds above, though it passes upward 

 into Thanet beds with fossils. The bottom bed of Thanet contain a -very 

 curious assemblage of sand grains 



Miss Gardner was quoted in a recent contribution to the Geological 

 Society as giving some details of the sands associated with the green- 

 coated flints in which she found : — 



" Quartz flint, Glauconite, and small quantities of Felspar and various 

 rarer minerals; viz., Magnetite and Spinel, Zircon, Garnet, Rubite, 

 Tourmaline, Actinolite, Calcedony, and casts of foraminifera. 

 At Pegwell Bay this unfossiliferous bed is 19 to 20 feet thick. 

 In other places it varies from one to two feet." 



In the recent cutting in the Mham Valley Railivay, East of Canter- 

 bury, the author remarked that this unfossiliferous Thanet bed is 

 largely developed and appears in places nearly 30 feet in thickness, but, 

 inasmuch as the clay drift above passes down so imperceptibly into the 

 beds below, it is difficult to determine the entire thickness ; there is, 

 moreover, an entire absence of fossiliferous beds in the tertiaries of the 

 entire cutting. 



