18 FOSSIL MEDUS 4. 
from the sea water without the intervention of any organic agency. In 
answer to this suggestion, and also to show the drift of opinion in relation 
to the origin of the silica forming the flints of the Cretaceous, I will quote 
the opinions and conclusions of several authors. 
In a contribution to the physical history of the Cretaceous flints,’ Dr. 
Wallich arrived at the following conclusions: 
1. That the silica of the flints is derived mainly from the sponge beds and sponge 
fields which exist in immense profusion over the areas occupied by the globigerine or 
calcareous ‘‘ooze.” 2, That the deep-sea sponges, with their environment of proto- 
plasmic matter, constitute by far the most important and essential factors in the pro- 
duction and stratification of the flints. 3. That whereas nearly the whole of the 
carbonate of lime, derived partly from Foraminifera and other organisms that have 
lived and died at the bottom, and partly from such as have subsided to the bottom 
only after death, goes to build up the calcareous stratum, nearly the whole of the 
silica, whether derived from the deep-sea sponges or from surface Protozoa, goes to 
form the flints. 4. That the sponges are the only really important contributors to the 
flint formation that live and die at the sea bed. 5. That the flints are just as much an 
organic product as the Chalk itself. 6. That the stratification of the flint is the 
immediate result of all sessile protozoan life being confined to the superficial layer of 
the muddy deposits. 7. That the substance which received the name of “ Bathyb- 
ius,” and was declared to be an independent living Moneron is in reality sponge 
protoplasm. 8. That no valid lithological distinction exists between the chalk and 
the calcareous mud of the Atlantic; and pro tanto, therefore, the calcareous mud may 
be and in all probability is a continuation of the Chalk formation. 
Dr. Sorby, in discussing these conclusions of Wallich’s, stated’ that he— 
had formerly studied this subject and come to the conclusion that, though deep-sea 
mud differs from chalk in many important particulars, yet still it was sufficiently 
related to warrant a comparison. Since the remains of siliceous organisms are absent 
from the chalk, but flint present, whilst in the deep-sea mud siliceous organisms are 
abundant and flints absent, probably the material of the flints had been to a greater 
or less extent derived from these organisms. Much, however, remains to be learned. 
Prof. W. J. Sollas, in his article on the flint nodules of the Trimming- 
ham chalk,*® in commenting on this argument, considers that it is not an 
analogy, but is in reality nothing less than a statement of fact. He then 
proceeds to prove that the Trimmingham flints have not only sponge spicules 
intimately associated with them in great numbers, but that the spicules 
afford clear proof of the previous existence of a great mass of spicules of 
1 Quart. Jour. Geol. Soc. London, Vol. XXXVI, 1880, p. 90. 
? Loc. cit., p. 91. 
‘Annals Mag. Nat. Hist., 5th series, Vol. VI, 1860, p. 438. 
