Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/113

1872.] SOLLAS UPPER-GREENSAND VENTRICULITAE. 69 contain. He states that while Brachiolites are found in the Lower Chalk and Upper Greensand, Ventriculites are confined to the Upper Chalk alone, occurring very doubtfully in the Middle Chalk, if at all; the identifications in this paper, however, show that the genus Ventriculites not only is not confined to the Upper Chalk, but is found abundantly as low as the Gault in England (for these Upper Greensand specimens are derived from the Gault) and still lower in the White Jura of the Continent. The occurrence of Ventriculites in the Oolitic formation does not tend to strengthen the affinities of the Chalk with our own times.

The analogy I drew in a former paper between the flints of the chalk and the coprolites of the Gault, receives illustration from these newly discovered Ventriculites; for precisely as the silicified Ventriculites are closely associated with obscure siliceous nodules or flints, and, with them, are instances of that remarkable fact the silicification of highly decomposable animal matter; so the phosphatic Ventriculites are closely associated with obscure phosphatic nodules or coprolites, and, with them, are striking examples of the phosphatization of soft-bodied animals.

For the valuable assistance I have constantly received throughout the preparation of this paper, my thanks are due and heartily tendered to the Rev. Mr. Bonney, of St. John's College. I have also much pleasure in thanking Mr. Jukes Browne (St. John's) and Mr. Jesson (Trin. Coll.), to whom I am indebted for many interesting specimens of our Cambridge Ventriculites.

Discussion.

Mr. J. F. Walker was not prepared to admit that all phosphatic nodules had been organized bodies, inasmuch as most of the fossil shells in the deposit were found filled with phosphatic mud of the same nature as the nodules.

Mr. Charlesworth also disputed the organic origin of the amorphous coprolites — and pointed out the analogies between the so-called coprolites of the Crag and those of the Upper Greensand, and the flints of the Chalk. He cited Ehrenberg as of opinion that the latter were masses of fossilized infusoria, while Dr. Bowerbank maintained that they were merely fossil sponges; and he drew the deduction that caution was necessary in accepting any theory as to the origin of the phosphatic nodules.

Mr. Seeley was not entirely in accord with Mr. Fisher as to the number of forms assumed by the phosphatic nodules. There were some that resembled common septaria; and in many cases the original form, especially in the case of the presumed Ventriculites, had been much modified by rolling on the sea-bottom. In support of the view of the sponge-origin of some of the nodules, he exhibited some of the modern forms of sponges enveloping different objects in the same manner as the phosphatic matter included shells and other fossils. Some of the Porospongioe in the Woodwardian Museum were, he said, not phosphatic, but calcareous fossils; and he thought some mistake had been made by Mr. Sollas in alluding to these specimens.