210 A FLAKE OF FLINT AND ITS HISTORY. 



CHAPTER XXI. 



A TLAKE OF FLINT AND ITS HISTORY. 



IN the foregoing chapter it was stated that the upper 

 white chalk, so far as hand specimens are concerned, is a 

 nearly pure limestone. This, indeed, is a perfectly true 

 statement as regards such hand specimens ; but when we 

 consider the upper chalk as a whole, we must not omit to 

 regard the numerous bands and nodules of flint with 

 which it is interstratified as a very important constituent 

 of the whole rock. We say a constituent of the whole 

 rock advisedly, because although the flint is now separated 

 from the white limestone which we call chalk in the form 

 of nodules and bands, yet there is evidence that it was 

 originally disseminated throughout the entire mass, and 

 that the upper chalk then formed a slightly siliceous 

 limestone. Probably everybody is more or less familiar 

 with flint as it occurs in a chalk-pit, or in the form of 

 gravel derived from the disintegration of chalk strata ; 

 but it may be taken for granted that comparatively few 

 have ever seriously considered how the solid masses of 

 flint have originated in the soft chalk limestone. As this 

 is a subject of considerable interest, and one which has 

 given rise to much discussion, we propose to devote the 

 greater part of the present chapter to its consideration, 

 while we shall add some observations on the history of 

 flints after they have been removed from their native 

 chalk. 



We shall assume, in the first place, that all our readers 

 are aware that flint is one of the manifold forms assumed 

 by that abundant constituent of the earth's crust technically 

 known as silica the oxide of the element silicon. When 

 crystallized, silica occurs in the form of rock-crystal, or 

 quartz ; but flint is one of the many non-crystalline, or 

 amorphous, developments of the mineral. It is generally 

 defined as a massive dark-coloured or black, semi-trans- 

 lucent, dull-looking variety of silica ; which when pure 



