R M. Brydone — The Origin of Flint. 403 



of massive and fully mature flints ; so does the miicronata zone in 

 the Isle of Wight at Alum Bay, and the mucronata zone of Norfolk 

 on the Weybourn-Cromer coast, and also at Trimingham (in the 

 white chalk). 



Another point not touched on by Mr. Eichardson is the frequency 

 of horizontal uniformity in variations in the flints. Take, for 

 instance, the flints of the upper part of the zone of M. coranguiyiwm 

 in Hants. In ]3roportion as the lJintacrinus-ha.xidi is approached, the 

 white cortex encroaches on the clear interior and assumes a pink 

 tinge, until the broken flints show nothing but pink cortex without 

 any clear centre ; and then it is time to look very closely for 

 Uintacrinus if it has not already been found. Or take again the 

 sponge-bed at Trimingham, which always has above and below it 

 a bed of long slender flints like no others that I have seen. Such 

 cases as these are much more suggestive of progressive formation 

 of flints under varying conditions of the sea bottom than of 

 simultaneous formation throughout many hundred feet of chalk 

 in a more or less uniform set of conditions. 



Mr. Richardson ignores the evidence of fossils, but there are 

 several indications to be drawn from them. In the first place there 

 are in the Chalk millions of specimens of Echinocorys perfectly filled 

 with chalk. The only avenues by which this chalk could enter are 

 the relatively minute apertures of the mouth and vent. It is clear 

 that the ooze in which these shells were immersed after the animal's 

 death must have been exceedingly fluid, practically liquid. With 

 these chalk-filled Echinocorys there occur millions of Echinocorys 

 perfectly filled with flint, yet having no vestige of flint on their 

 outsides. Occasionally specimens of Echinocorys are found in which 

 the interior is partly filled with chalk and partly with flint. In these 

 cases there is always a definite boundary between the chalk and the 

 flint. I have never seen any indication of sporadic silicification in 

 the chalk inside an Echinocorys. These considerations seem irre- 

 concilable with any metasomatic theory of the origin of the flint. 

 In a medium so fluid as the ooze is shown to have been, nothing 

 could have prevented it from filling those Echinocorys which are 

 now silicified, except the presence of the dead body of the animal. 

 As that decayed it must have been replaced by ooze unless the silica 

 had already installed itself, and silica arriving at any later date 

 would have found these Echinocorys completely filled with ooze. 

 How are you going to arrange in a more or less consolidated deposit 

 (on the uplift drainage theory a deposit hundreds of feet in thickness 

 and almost necessarily consolidated) for the concentration on the 

 two small apertures of a small proportion of the Echinocorys present 

 in the chalk of streams of silica of exactly sufficient force, purity, 

 continuity, and volume to displace every particle of chalk from the 

 interior of these Echinocorys without the very slightest overflow of 

 silica ? The conclusion that the silica got there before the ooze had 

 a chance seems irresistible. It is not difficult to see that the distinction 



