Flints of the Upper or White Chalk. 187 



the combined mass of colloidal silicic acid and protoplasm to 

 contract upon itself, and thus to bring about, by slow and sure 

 degrees, the separation of its combined water. But it is not 

 until the transition is actually imminent, from the plastic con- 

 dition of the still nascent flint nodule to the final consolidated 

 state when the nodule may be regarded as complete, that the 

 minute residuum of water, enabled under the enormous pres- 

 sure to retain a portion of pure silica in solution, yields, for 

 the first time since it formed a component portion of the sili- 

 ceous mass, to purely chemical forces, and thus, by dialytic 

 action, escapes in its elementary form from its long imprison- 

 ment. It is during the entire period, dating from the death 

 of the parent organisms that furnish the silica and protoplasm, 

 up to that at which the final consolidation takes place, that the 

 innate tendency to the assumption, by the continually con- 

 tracting mass, of the peculiar external forms which so signally 

 characterize the flint nodules, exercises a determining effect 

 upon them — this effect being in all probability at its maximum 

 of energy in the early stages of the masses, and at its minimum 

 in their latest stages, but never absent or materially inter- 

 rupted in the quiescent solitudes of the ocean. It shall be 

 shown hereafter that dead and effete albuminoid matter^ as well 

 as living^ evinces this tendency to assume what I have termed, 

 in the absence of a preferable word, amoebiform outlines. 



The varying number and contiguity of the flint nodules in 

 different strata of chalk, and in different parts of the same 

 chalk-beds, prove that these variations are due to varying 

 extent, bulk, and rapidity of growth of the sponge-fields and 

 their enveloping nidus of protoplasm, both the siliceous and 

 the albuminoid portions of these organisms being contributories 

 to the flint-formation. Did the nodular flints really originate, 

 as alleged by Mr. Sollas, in silicified chalk — if by this expres- 

 sion we are to understand that a siliceous solution derived 

 from the solvent action of sea-water on the spicules, aided by 

 a partial admixture with the products of decayed organisms, 

 " replaced the calcareous material of the ooze, . . . that siliceous 

 chalk (not flint) was the result, . . . and, subsequently, this 

 siliceous chalk became converted into black flint, an incom- 

 pletely silicified layer of chalk remaining as the white layer of 

 its surface" — it is very difficult, if not impossible, to conceive 

 why or how such flint assumed, under any ulterior conditions 

 short of re-solution and combination with a plentiful supply of 

 colloid matter, the amoebiform outlines I have so often alluded 

 to. The replacement of carbonate of lime — whether in sponge- 

 cavities, shellsjthe tests of Foraminifera, or masses of calcareous 

 ooze — has never^ that I am aware, been found coupled with 



