304 Obfervations on the Flints of Chalk-beds. 
phenomena; nor could I acquiefce in any of the 
various explanations which - mineralogical writers 
have offered. I inclofe the few obfervations I made 
upon thefe curious bodies, and requeft that you 
will lay them before your Society. 
I. It is well known that flints occur, for the 
moft part, ftratified. They feldom touch one another 
in the bed, but lie infulated, like the fpecimens in 
the drawer of acabinet. In almoft every ftratum, 
I believe, nodules alternate with tables, or flat 
maffes, varying in thicknefs and extent. I did, 
however, obferve flints irregularly difperfed among 
the chalk. Suppofe the floor of a room to bea 
flinty flratum, and the cieling a fieve, through 
which chalk is falling; fuppofe, at the fame time, 
that a by-ftander toffes pebbles occafionally among 
the defcending fand, and you will have an idea of 
the manner, in which thefe folitary maffes are dif- 
perfed through the chalk. 
II. The rough white cruft, which furrounds each 
flint, and is at firft fight fo naturally miftaken for 
adhering chalk, is formed in confequence of the 
decay of the external coat of the flint itfelf. It 
perhaps is the immediate effect of the decompolition 
of the water that foaks through beds. ‘That it is 
owing tothe decay of the flint , evidently appears 
from the change that takes place on the frefh face of 
fragments, broken for the repair of the roads. 
Thefe fragments, after a fhort expofure to the wea- 
ther, become tarnifhed; by degrees they turn 
milky 
