270 G. Abbott—Contemporaneity of Chalk and Fiints. 
If, however, we may use this as a working hypothesis that tabular 
flints “grew” by gradual accretion and quite independently of any 
organic agency, can we any longer believe they were formed even 
partially when the Chalk was beneath the sea. The upper part of 
the Chalk would then have been in the condition of soft ooze, and 
even if cracks were formed, the spaces would have been quickly 
filled with cretaceous matter and the deposit of flint rendered im- 
possible owing to the length of time it would have taken to 
‘‘grow ” on the walls of the cleft. 
Very much of course depends on the settlement of this question. 
Will someone point out if it is unreasonable to look in this direction 
for a solution of our difficulties in reference to chalk flints ? 
If any of the old theories or even that of segregation below sea- 
level be applied to special forms of flint—paramoudra for instance— 
they fail to answer even the most obvious questions. The old idea 
that these potstones originated in cup sponges has been discredited 
because of the difficulty of understanding how sponges could grow 
out of one another and extend in great columns like paramoudra, 
through the height of the cliff. Unfortunately I have had no chance 
to examine them in situ, and therefore only hesitatingly suggest 
that their origin was entirely independent of animal organisms, they 
being merely broken pipes of silica which formed in the chalk sub- 
sequent to its elevation above sea-level. The silica might have been 
supplied by the percolation of water through the overlying arenaceous 
strata, while each section of the broken pipe after its slight dis- 
placement by the movement of the Chalk which led to its fracture, 
would probably still act as a centre for further deposits of flint, and 
thus all traces of fracture would soon be obliterated. 
Both paramoudra and tabular flint I believe to have been caused 
by the deposit of amorphous and crystalline forms of flint in chalk 
cavities—each by gradual growth extending in the direction of least 
resistance, without depending upon the help of organic remains, but 
enveloping and matting together any substances close at hand. 
Careful observation of an immense number of other specimens 
leads me to suggest that in spite of the bossy, irregular forms assumed 
by flint, it has increased after the same manner as other concretions. 
This condition is much obscured by the presence of colloidal silica, and 
has perhaps not been observed because it was not expected or looked 
for. Instances, however, can be well seen in the interior of hollow 
flints with cores, supposed to be the silicified casts of the cloace of 
Siphonie. Although these cores correspond as a rule to the long 
axis of the cavity, yet there are frequent exceptions. Smaller 
secondary cores, too, are often present lying at various angles and 
blending into each other. 
It has long been accepted as a fact that flint has often com- 
menced to form in chalk by means of sponges, many of which were 
subsequently removed after acting as a sort of scaffolding for the 
flint. This explains the numerous hollow flints met with. To these 
organisms we must add many others, such as wood, shells, ete., 
which have acted as centres for the segregation of flint. 
