Art. XL.—On the Tertiary Series of Oamaru and Moeraki.*
[Extract from a letter to Dr. Hector, May 25, 1869;—read before the Wellington Philosophical Society, September 18, 1869,]
I Beg to communicate some observations concerning a formation which, in this district, rather puzzles me. I call it the “Blue clay” formation for want of a better name, that being the usual term for the principal deposit of it that I have seen. Very near Hampden, a well, sunk by Mr. Gleeson, for, I believe, 300 feet, did not penetrate through it; but it is often yellow or yellowish-brown, and not unfrequently forms hard rock, as you are doubtless aware. I myself have not noticed it north of the lower Waitaki, south of the Moeraki boulders, or west of Mr. Feren's station on the Kakanui, but have seen specimens of it from other parts of Otago and Canterbury. You probably know whether the Awatere blue clay contains similar fossil remains or not.
Some time since I was endeavouring to work up the fossil shells of this formation, with the view of determining approximately the proportion that has become extinct.
Of course, in a collection of fossils, we must expect a number on which we cannot pronounce with certainty, by reason of their imperfect condition, as I need hardly say; but I have been at pains to procure and lay bare, at least one good specimen of each species, so as to reduce the doubtful cases to a com-paratively small number. Striking these off until further light is thrown on them, and reckoning, on the one hand, those between which and the recent I am unable to distinguish any difference; and on the other hand, those which
[Footnote] * See Mantell, “Quart. Journ. Geol. Soc.,” Vol. vi, p. 333.—ED.
are clearly distinct; I feel now pretty confident that we must consider more than one-half of the species to have become extinct in our seas. This alone, if confirmed by further and more extended observations, would, I presume, prevent this formation being referred to any period later than the Miocene; though, as far as I can make out, by the works I have by me, it has always been considered as Pliocene or Pleistocene, (see Hochstetter's “New Zealand,” p. 61—“Younger Tertiary Strata,” etc.)
Doubtless some of the species may be extinct here, and alive elsewhere, but I fancy this is improbable. The presence of several of the genera, as Cassidaria, Conus, etc., seems to indicate, if anything, a somewhat warmer climate, but I see no approach to the shells of Port Jackson, in the latitude of the North Cape.
Of the Chilian shells (I did pick up shells there ages ago), I have little recollection.
It appears to me, however, that the proportion of extinct species is much less striking than the number of extinct genera. Woodward writes, p. 421, “The shells of the newer tertiaries, are always identical, at least generically, with those of the nearest coasts.” But here we have the following genera, none of which, as far as I know, have been found recent.
Typhis (the Rev. Mr. Taylor's Typhis, was, I think, a Murex), Pyrula, Cassidaria, Conus, Sigaretus, Turritella, Avicula, Perna, Cucullæa, Limopsis, Crassatella, Mya, with one of the sub-genera of Natica.
I shall append a list of all the genera I have determined, and when you come this way I can show you these and other specimens.