Note on the ORBITOIDES and Nummulinae of the Tertiary Asphaltic Bed TRINIDAD.
By Professor T. Rupert Jones F.G.S.
The asphaltic rock yielding Orbitoides and Nummulinae in abundance is described in the 'Report on the Geology of
Trinidad' (1860, p. 37), by Messrs. Wall and Sawkins, as a highly inclined bed of bituminous shelly marl, protruding
on the coast at San Fernando, on the west side of the island, and forming part of the "Naripima Marl,"
in the "Newer Parian Group," regarded as being probably Miocene, whilst the "Older Parian,"
on which it rests, is Neocomian in age.
In 1863 Mr. R. L. Guppy read a paper descriptive of this peculiar stratum before the "Scientific Association"
in Trinidad, pointing out that its shelly contents are Orbitoides and Nummulites, the former predominating; and
he suggested that in all probability they would be found to be of the same species as those referred to in 'my
" Note on the Nummulinae and Orbitoides of Jamaica "(Quart. Journ. Geol. Soc. vol. xix. p. 514). This
opinion is confirmed by a careful examination of specimens of the asphaltic stratum, with which Mr. Guppy has favoured
me.
Boiled several times in turpentine, this rock loses its bitumen, and resolves itself into loose Orbitoides and
Nummulinae with a few other Foraminifera, and (when cleaned by acid) a small proportion of green-black sand and
very few rounded grains of quartz. On the weathered surfaces of the rock, and in pieces carefully burnt, many perfect
Orbitoides may be recognized; and probably throughout the mass the specimens are mostly well preserved; but it
is difficult to get them out whole and clean, except by long steeping in hot turpentine, changed from time to time.
The Nummulinae keep rather more perfect in the process of cleaning. The many aspects, however, of the broken specimens
enable us to determine their relationships without the trouble of grinding and polishing. When the asphalt is driven
off by heat, the Nummulites often fall into two pieces by splitting along their median line of chambers; but this
horizontal section is not generally so useful in determining species as the exposure of the successive surface-layers.
The majority of the Orbitoides, mainly constituting this rock, are small and biconvex, with somewhat expanded edges,
about 1/8 inch broad and 1 inch thick at the centre. There are also occasional evidences of broader thin Orbitoides.
The Nummulinae, not nearly so numerous, are smaller still; biconvex, with a sharpish edge, and measuring about
1 / 12 by inch. A fragment of a small Nodo saria raphanus and a Discorbina also occurred to me, together with a
piece of a little Echinoderm-spine.
The Orbitoides is exactly the same as the variety from the Tertiary sand of Orakci Bay, New Zealand, described
and figured by Karrer, in the 'Novara Expedition' (Geol. Theil, I. Band, 2. Abtheil. Palaeont. p. 86, p1. 16. fig.
21), as 0. Orakeiensis, Karrer; which, there is reason to believe, is a variety of O. Mantelli, Morton, a species
found in America, the West Indies, and Sinde (see Geol. Mag. vol. i. p. 75, and p. 103). The Nummulite is one of
the small "sinuo-radiate" varieties (sometimes simply "radiate"), such as are referred to by
me in the note on the Jamaican Nummulinae, and in the 'Geol. Mag.' loc. cit., as present in the West Indies, Sinde,
and Europe (Vienna) in rocks probably of Middle Tertiary age. It may be catalogued as N. Ramondi, Defr. (=N. radiata,
D'Orb.), which is found associated with Orbitoides in Jamaica, Antigna, and Sinde.
Proceedings of the Geological Society, 1866, p. 592 - 593
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