of the Flints of the Upper Chalk. 



11 



the bottom is flat and all around tlie ridges rise regularly and 

 concentrically; giving necessarily the idea of some liquid sub- 

 stance, of which the surface was very rapidly solidifying, and 

 disposed altogether to very rapid soliditication, and which at the 

 exact moment of such condition was affected by some small 

 rapidly revolving eddy, while the other parts of the solidifying 

 substance were at the same moment affected by small but rapid 

 currents running in opposite directions. This very motion pro- 

 bably caused the solidification of the mass, for, curiously enough, 

 there are fewer marks of organic remains in this and another 

 similar Hint than in any others I possess*. The edges of all 

 the ridges are sharp, although in this instance, contrary to what 

 we shall presently find in another, the whole surface, under the 

 angles of the ridges as well as above them, is covered with the 

 mealy coating. The under surface of this flint is covered with 

 ridges precisely in the same manner as the surface figured, and 

 in a manner which renders the specimen still more striking as 

 illustrating the action of the supposed currents. Traces of the 

 flakes which have thus been forcibly slipped over each other are 

 also observable in the substance of the flint, at a cross fracture, 

 precisely as might be the case where flakes of ice, slipped over 

 one another, varied slightly in colour, from some contained sub- 

 stance, while separately exposed and before being piled over by 

 a mass of other liquid, on whose thus forcibly and rapidly 

 upraised surface the broken edges of other flakes would of 

 course be seen ; and the whole of which mass, so piled up and very 

 rapidly solidified by the 

 very agitation thus given, 

 affords the most exact idea 

 of the present specimen. 

 I have another specimen 

 presenting exactly the 

 same general characters of 

 liny ridges with sharp over- 

 lapping edges, though the 

 form assumed is different. 

 I have also a most inter- 

 esting section of flint, pre- 

 senting, under the micro- 

 scope, evidence of a pre- 

 cisely analogous train of 

 facts and consequences. 

 This specimen, which is 

 here figured, speaks for 



* " The slightest disturbing causes, as agitation, cliange of temperature 

 or the affinity, though slight, of some other body for the solvent, would put 

 an end to the solution." — Turner's Lecture, as before cited, p. 26. 



Traces of revolving particles in flint mag- 

 nified about four linear. 



