Mr. Rose's Sketch of the Geology of West Norfolk. 371 



strata of tabular flints, placed at distances from each other, 

 varying from three to eight feet. At Swaffham two layers 

 occur but twenty inches asunder*; here also the tabular flints 

 are of great magnitude, many of them being eight or more 

 feet in length, and from nine to twelve inches in thickness. 

 Many nodules of flint are interspersed throughout the chalk, 

 the majority of them small, and receiving their form from a 

 zoophitic nucleus; larger flints thus situated are less fre- 

 quent : the Paramoudra is very rare, I have seen but one ; 

 but at Thornham the chalk " contains enormous Paramou- 

 drsef." At Hilborough the uppermost layer of flint, at the 

 depth of twelve feet from the surface, is a thin seam, varying 

 in thickness from one eighth to an inch, some of the thicker 

 parts having the appearance of two thin plates cemented to- 

 gether ; about eighteen inches below this occurs a layer of 

 nodular and cylindrical flints, running horizontally, and pa- 

 rallel to the seam. Similar thin seams were observed near 

 Wells by Mr. Woodward, " traversing the chalk, both in a 

 horizontal and oblique direction ; and in many parts they do 

 not exceed one eighth of an inch in thickness J." I found 

 also at Thetford thin tabular flint, not more than half an inch 

 in thickness ; the first layer occurs at about ten or twelve feet 

 below the surface, and lies parallel to the stratification of the 

 chalk : the lime-burner informed me that at the depth of twenty 

 feet three layers of similar flint succeed each other at about 

 a yard asunder, and that the flint is invariably found fractured 

 in every direction. Each slab of flint appeared to be formed 

 of two plates in apposition, the flint in the line of junction 

 being of a lighter shade : this character was very apparent 

 upon the recently fractured surfaces. In one instance I ob- 

 served drusy crystals of quartz between the plates. Does not 

 this laminated structure offer an illustration of the mode of 

 formation and arrangement of the flinty strata? and does it 

 not favour the opinion, that the siliceous molecules, by elective 

 attraction, separate themselves from the calcareous matter, 

 above and below certain parallels determined by the proportion 

 of silex contained in the chalk, and approach each other until 

 they arrange themselves in the tabular form § ? 



The chalk at Thetford abounds in flints, which partake 



• Mr. Woodward informs us that similar lt double rows of flints" occur 

 in East Norfolk. See Geology of Norfolk, p. 24. 



f Mr. R. C. Taylor's Paper in the Geological Transactions, Sec. Ser., 

 vol. i. p. 378. 



X Geology of Norfolk, p. 27- 



§ When the masses of clay mixed with ground flints, prepared for 

 making fine pottery and china, " are allowed to stand unused for some 

 time, it often happens that the particles of the powdered flint separate 



3 B2 



