On the Discovery of Organic Remains in the Caribbean Series of Trinidad
Authors: Guppy R. J. Lechmere 
Published: October 2009

Abstract

T
he
author described the formation called the “Caribbean Group” by the Government Geological Surveyors of the West Indies as forming a considerable portion of the littoral cordillera of Venezuela, and as extending eastward through the north of Trinidad to Tobago. It consists of gneiss, gneissose, talcose, and micaceous slates, and compact limestones. The metamorphic rocks of Guiana lately described by Mr. Ralph Tate (Quart. Journ. Geol. Soc. vol. xxv. p. 343) are regarded by him as of the same age as those of the littoral chain of Venezuela; and it is probable that the series occurs again in New Granada. Mr. David Porbes mentions the occurrence of gneissic and metamorphic strata on the Bolivian coast and in the desert of Atacama. According to M. Pissis, an extensive series of micaceous and gneissoid strata underlies the Silurian beds of Illimani in Bolivia; and Mr. Darwin alludes to strata of clay-slate &c. older than the Silurians of the Chilian Andes. The author considered that the Caribbean formation will be found to mark one of the “stable areas” insisted upon by Prof. Dana.

The northern range of mountains of Trinidad is composed entirely of rocks belonging to the Caribbean formation. The section from N.N.W. to S.S.E. from the sea, through the valleys of Diego Martin, Maraval, and St. Ann, shows the following succession of rocks in ascending order:—
1. Mica-slates, with quartzose sandstone; 2. Crystalline limestone; 3. Argillaceous slates, with hard sandstones, conglomerates, and thin beds and strings of calcareous matter; 4. Compact limestone, forming the Laventille hills bordering the plain of Caroni.
The total thickness of these rocks in Trinidad is stated by the author at upwards of 10,000 feet; and he is of opinion that the thickness of the whole group is many times greater than this, a portion of the series in Venenzuela being probably inferior in position to the rocks exposed in Trinidad. A high angle of inclination almost everywhere prevails, the general range of dip being from 30° to the vertical.

After noticing the difficulty which has hitherto existed in determining the age of the Caribbean formation, from the want of fossil evidence, the author stated that he has found undoubted traces of the existence of organisms during the deposition of these rocks. In the uppermost compact dark-blue limestone (No. 4) obscure fossils occur. In the clay-slates and quartz-rocks (No. 3)underlying this limestone there are strings and bands of calcareous matter which sometimes contain fossils. In a portion of one of these strings found by the author about 3 feet below the surface in the decomposed mica-slate forming the soil of one of the valleys, he detected a structure which he regards as of animal origin, and as probably most nearly related to
Eozoon
. He was unable to detect any traces of tubulation in it, but suggests that this character may have been obliterated, as in the Tudor specimen (Quart. Journ. Geol. Soc. vol. xxiii, p. 257). The chambers are said by the author to be more elliptical than those of
Eozoon canadense
; and for this and other reasons he proposed to regard it as a new species, under the name of
Eozoon caribbæum
.

Associated with this supposed
Eozoon
, the author has found other remains. These include fragments of coral, some of which are stated to resemble
Favosites
, although no pores or tabulæ could be detected in them. These fragments are thought by the author to have belonged to a minute branching
Favosites
, which he proposes to name
F. fenestralis
. Plates and stems of Echinoderms are scattered through the rock. The author particularly described a specimen consisting of five ambulacral plates, with four pairs of pores, and another fragment showing portions of at least twenty ambulacral or pseudo-ambulacral plates, reminding one of those of the Devonian
Eleacrinus
.

The author has found that the bands of calcareous matter interstratified among the slates are seldom devoid of organic remains, except when they are very highly metamorphic. In a finely laminated limestone he found great abundance of obscure fossils, many of which appeared to be remains of Cystidea, whilst others resembled annelid-tubes, like
Salterella
.

The author suggested that the function of
Eozoon
in pre-Cambrian times was analogous to that of corals at subsequent periods. He considered that there is the highest probability that the Caribbean series will ultimately prove to be pre-Silurian.