284 



The Twenty-Ninth General Meeting. 



on the sea-bottom of silicious sponges has been supposed to indicate 

 that under the enormous pressure of the deep ocean, and in the 

 presence of accumulated and accumulating" silicious remains of poly- 

 cistina and other silicious organisms, the dissolving action of the 

 water on the colloid silica so accumulated may be enhanced ; or, on 

 the other hand, it may be that the opposite result might take place, 

 and that the dissolved silica in the sea would more readily separate 

 in gelatinous form under the conditions of the sea-bottom. It 

 seems probable that in one way or other colloid silica is accumulated 

 in the neighbourhood of the sponges; but if it-be not so, time, ihe 

 inexhaustible paper-money of the geologist, has only to be drawn 

 upon largely and the sponges would be as completely (perhaps more 

 entirely because more gradually) saturated with the silicious ingre- 

 dient which is now flint. An answer to the second question has 

 been given by Dr. Wallick. The Atlantic ocean-floor is at this day 

 covered, over considerable portions of its area, by a species of slime 

 which has had many explanations. It is of the nature of an or- 

 ganism of an elementary type, presenting sarcoid characters under 

 the microscope. Dr. Wellick considers it to be what he calls sponge 

 protoplasm. Whatever it be, it is associated with the globigerine 

 (a foraminiferous) ooze which forms the deep mud of the Atlantic, 

 and which is so nearly identical in feature with the chalk as the 

 chalk must have been when itself a white mud, that the question 

 is gravely asked whether the chalk ocean has ever ceased to roll from 

 the day when a great part of Europe was under its waves, to this 

 day, when its boundaries are the shores of the Atlantic. Dr. 

 Wellick''s view is that during the period when the upper chalk was 

 being formed this light protoplasmic film may be said to have in a 

 certain sense floated on the denser foraminiferous mud ; that the 

 silicious materials of dead organisms fell on it and accumulated 

 there ; that the amount of silica in an assimilable form continually 

 increased in that horizon of the ocean, as a consequence ; and that 

 the Porifera so formed the best conditions for their growth. 



After a time the accumulations of silicious organisms and ma- 

 terial became too compact for buoyancy, and then the layer con- 

 taining them became fixed in situ } while over it fresh generations of 



