154: MR. F. D. LONGE ON THE FORMATION OF FLINTS IN CHALK. 
or belemnites, partially enveloped in a Hint nodule, but which, in 
some cases, have not been silicified. 
I have a specimen of a belemnite half in and half out of a flint. 
The substance of the fossil is the same inside the flint as outside. 
It is an ordinary crystallised belemnite, and the substance is pure 
carbonate of lime (aragonite). 
This belemnite must have been in this crystallised condition 
before it became partially enveloped in the growing flint. Relics 
of organic life, or other foreign substance, may provoke concretionary 
action ; just as foreign substances provoke crystallisation, but they 
are not necessary to the origin of a flint or any other mineral 
concretions. They are common as curiosities and freaks, rather 
than as representative of the normal growth of flint. However they 
originated, the formation of flint concretions has apparently been 
to extract and gather together the silica disseminated through the 
chalk, so as to reduce the material of the “ upper chalk ” formation 
to a much purer carbonate of lime than that of other chalk 
formations. 
The flint nodules in Norfolk chalk pits may be classed in 
three groups. 
(1) The larger, or, as I would say, the full-grown nodules, are 
generally of tuberculous or knobly forms, and are found lying in 
horizontal lines about eight to ten feet apart. 
These larger flints have generally a very thin coating of silicious 
material if any ; the granular silica having been all absorbed in 
the flint. 
The arrangement of these large nodules in horizontal layers 
would appear to be due, in part, to the action of gravity in 
bringing down the granular silica, as in the formation of layers of 
chert. 
(2) Another class, and by far the most numerous, are the smaller 
forms, round or egg-shaped, sometimes long finger-shaped nodules. 
These are found distributed apparently without any system or 
regularity between the layers of large flints. This class includes 
the “ baby flints.” 
These whole flints are always more or less round, and the 
surface is similar all over the pebble. It is generally of a 
bluish colour (except when stained by peroxide of iron), and 
shows markings or indentation, which belong to the original 
