206 



THE GEOLOGIST. 



we must consider the Pointe a Pierre deposits as undoubtedly equal 

 to or older than the true chalk. 



Numerous fragments of an oyster somewhat like Ostrea carinata, 

 a fossil of the Lower Greensand, are found with the Trigonia. I 

 have not however been able to obtain a perfect specimen. At the 

 same locality I have found oysters referable, perhaps, to two other 

 species. One of these is a good deal like the recent Ostrea edulis, 

 and one of my specimens shows the markings of the hinge cartilage 

 very distinctly. I have also found a single valve of a deeply sulcated 

 bivalve, which may be an Avicula, but which presents some resem- 

 blance to a fossil described by Yon Buch as a Pecten under the name 

 of Pecten alatus* My specimen, however, has fewer sulcations than 

 the shell described by Yon Buch, and the absence of wings makes 

 the determination somewhat uncertain. It is possible, however, that 

 the shell in question may be a young specimen of P. alatus. 



Gasteropoda are also represented among the fossils from Pointe a 

 Pierre, but the specimens are generally so imperfect as to render the 

 determination of their relationships difficult. A cast in my possession, 

 upwards of 2 inches in length from the apex to the peristome, seems 

 to be of a naticoid type. Another cast, which has some shelly mat- 

 ter remaining on it, is very like a cast figured by Yon Buch as a 

 Eostellaria, and may belong to the same species.f 



A single valve, embedded in a calcareous nodule, from Pointe a 

 Pierre, appears to have belonged to a Plagiostoma, while a massive 

 gibbous valve about 2\ inches in length, has some of the characters 

 of a Cytherea ; but that genus is not common in rocks of such ancient 

 date. Amongst the fossils collected by me, are several other frag- 

 ments of Mollusca, which appear to be indeterminable. Still, though 

 there is much doubt respecting a great part of the fossils yet col- 

 lected from these deposits in Trinidad, enough has been discovered 

 respecting them to confer a character of greater certainty on the pre- 

 sumption of the age of the Older Parian deposits in this island than 

 has been previously attained to. 



All the fossils I have been able to obtain from Pointe a Pierre 

 have been from the beach • consequently, they are usually much 

 worn, and it is hardly possible to ascertain from what portion of the 

 group they have been derived. The Trigonia and the oysters are 

 tolerably well preserved, as far as their structure goes ; but the shells 

 of the Gasteropoda have nearly disappeared. The thick and massive 

 character of the shells is worth notice, and it prevails alike in all the 

 specimens in which the test is preserved. 



Prom what I have said in this paper, it will be seen that the pa- 

 lreontological evidence is in favour of Mr. Etheridge's view % of the 

 age of the deposits termed " Older Parian " by the Government geo- 

 logists. Until, however, more fossils can be obtained, and their 

 position in the series better determined, it will be as well to leave 



* Von Buch, ' Petrifactions recuellies par Humboldt,' pi. i. figs. 1, 2, 3, 4. 

 t Von Buch, ' Petrifications,' pi. ii. tig. 27- 

 % Report on the Geology of Trinidad,, p. 163. 



