251 CHAPTER XVII THE GEOLOGICAL RANGE OF THE FORAMINIFERA In commencing a survey of the various foraminiferal faunas of past ages we might naturally expect to find the remains of such lowly organised and adaptable creatures as Foraminifera in great abundance in the oldest fossiliferous rocks. But this does not appear to be so, for the older Palæozoic series has up to the present yielded very few genera and species of this type of animal life. At one or two horizons only are their remains found in tolerable abundance, and these are generally in the form of glauconite casts. On the other hand in these oldest rocks certain examples have been found which have the hyaline type of shell, and in which the original structure has been wonderfully preserved. The majority of the older Palæozoic Foraminifera have been assigned to genera of the perforate type, such as Lagena, Nodosaria, Globigerina, and Spirillina, whilst in strata of later age in the same era the arenaceous genera Hyperammina, Stacheia, and Textularia make their appearance. Seeing that the shells of the Foraminifera which are as a rule so well preserved, especially in calcareous strata, as the limestones and calcareous shales, are comparatively rare in the older rocks, we may reasonably infer that the types of Protozoa, which very probably existed in earliest times and in prodigious abundance, were chiefly represented by those forms which did not possess an investment of hard material, but consisted merely of sarcode, or perhaps were covered by a thin chitinous investment. This conjecture, however, will require proof which prima facie will be next to impossible to obtain, for the chitinous forms are practically unknown as fossils. It appears by recent researches to be pretty conclusively proved that the whilom sensational Eozoon Canadense of the Laurentian limestone rocks of Canada and elsewhere is not a gigantic foraminifer. Whether it be a purely mineral structure or a mineralised organism of a larger type of growth, such as a hydrozoan, remains to be seen; it will not be necessary to dwell further upon it here. Some exceedingly minute bodies resembling Foraminifera in their general form have been described by Cayeux from the Pre-Cambrian of Brittany, where they occur in quartzites and pthanites. They are, however, of such small dimensions, the largest of their segments having a diameter of only 3 inch, that their relation to Foraminifera may be considered somewhat doubtful. 237 Ehren Four noteworthy occurrences of Foraminifera have been recorded from Cambrian strata. berg, in 1858, figured various glauconitie casts of Foraminifera from the so-called Silurian clay' near St. Petersburg, which apparently belong to the genera Verneuilina, Bolivina, Nodosaria, Pulvinulina, and Rotalia. This blue clay of the Baltic Provinces is now known to belong to the Lower Cambrian, for it underlies the Olenellus beds. Other examples of glauconite casts of these organisms had been previously figured by Ehrenberg in 1855, and discovered by him in the glauconitic sandstone near St. Petersburg. The Hollybush Sandstone of this country, also of Lower Cambrian age, often largely consists of bright green glauconite casts of Foraminifera, embedded in a ferruginous and argillaceous cement, the casts resembling small forms of Globigerina. Evidence of an old foraminiferal fauna has been brought to light in Southern New Brunswick by Messrs. W. D. and G. F. Matthew, who discovered these microscopic fossils in the Arcadian or lower division of the St. John's series. They have been referred by the above authors to the genera Globigerina and Orbulina. The Cambrian strata of Siberia have, according to De Lapparent, lately yielded foraminiferal remains in some abundance in the limestones of a plateau traversed by the Olenek. An interesting discovery of an Upper Cambrian foraminiferal fauna in a shaly limestone near Chase End Hill, in Shropshire, was lately made by Professor Groom, and the organisms have been described by the writer. The collection comprises a number of genera with hyaline tests which are very well preserved, the tubuli of the shell-wall appearing quite distinctly in |