NOTES ON THE SPEETON AMMONITES.

BY C. G. DANFORD.

Anyone who knows a little about the Speeton sections can soon pick up a fairly representative series of their Belemnites, but not of their Ammonites; that demands much time and luck. Such at least has been my experience, for notwithstanding the exceptional opportunities for constant search afforded by several years' residence almost on the spot, I have not yet found some species, only poor examples of others, and -proof of the exhaustive character of Prof. Pavlow's and Mr. Lamplugh's museum and field researches-hardly any that cannot be identified from the descriptions and figures in their "Argiles de Speeton,"* to which work I am further indebted for the nomenclature and the classification of the series† used in the following slight sketch.

The Ammonites at Speeton are not only in much worse condition than the Belemnites, but also far fewer, except in the Kimeridge, where their crushed remains are legion, while in a considerable part of the upper deposits there are apparently none.

Of the 43 species described or figured in the "Argiles de Speeton," all but four, representing as many genera, are inIcluded in Hoplites and Olcostephanus, the latter being divided

"Argiles de Speeton et Leurs Équivalents," par A. Pavlow, et G.W. Lamplugh, Moscou, 1892.

†The main divisions are indicated by letters, their sub-divisions by numerals.

In the Table of the Cephalopoda of the Speeton Series," ("Further Notes on the Speeton Section," &c., Q. J. G. S., vol. lii., 1896, p. 181), Mr. Lamplugh adds to these, Hoplites Mortelleti, Pict. and Lor., C8-11?, H. interruptus? Brug. A., Olcost. (Simbirskites) versicolor? Trautch., Olcost. (-) cf. Carteroni, d'Orb, C1 to upper part of C6?, Oxynoticeras cf. catenulatum, Fisch. D4-8. He also notes the probable presence in D4 of Olcost. plicomphalus Sow.

by Prof. Pavlow into six groups, or sub-genera, Virgitates, Craspedites, Polyptichites, Holcodiscus, Astieria, Simbirskites.

66

The Hoplites occupy the lower part of the upper Kimeridge, the extreme top of the Lateralis zone D, the lower part of "the Jaculum zone "C, the top of the Brunsvicensis zone B, and "the Minimus zone " A; the Olcostephani, occur in the upper Kimeridge, the Coprolite Bed E, the entire Jaculum zone, and the extreme base of the Brunvicensis zone. The species not included in these two genera occur in the Kimeridge, the middle of the Jaculum, and the top of the Brunsvicensis zones.

ZONE F (KIMERIDGE CLAY).

The greater part of the Kimeridge is terra incognita, for there is no record of its base and middle having been seen even by the earlier collectors, though they appear to have been vouchsafed better exposures of these shales than their suc

cessors.

The beds with Amm. biplex (= Perisphinctes lacertosus) Amm. evalidus (= Hoplites eudoxus), together with other fossils described by Leckenby, and those from which Mr. Herries subsequently collected the same species are the lowest that have been observed. Among their Ammonites preserved in various museums, Prof. Pavlow recognises H. pseudomutabilis Loriol and H. subundora Pavl.

During the early part of the present year there were several slight and fugitive exposures of these deposits 200 to 300 yards north of Reighton Gap, i.e., about half a mile from Speeton Middle Cliff Ridge, at the base of which the Kimeridge and the Coprolite seam above it are always more or less visible. A striking feature of the most northerly was a band of septarian nodular matter about a foot thick, which rested on greenishblack shale. This band at first showed as an almost unbroken reef, but was soon breached by the heavy seas, so that if seen again at the same spot it will not present its original continuous appearance. The beds below it were alternately greenish-black

Figs. 1, la. Oleostephanus (Polyptychites) bidichotomus Leym. D2 base. 17821."

2, 2a.

*

D2 base. 17823.

) polyptychus Keys. D2 base. ) cf. Keyserlingi Neum. & Uhl. Scale t

17822.

The numbers refer to the numbers of these specimens in the Catalogue of the Geological Museum, Jermyn Street. + Owing to a slight reduction in the making of the blocks in this and the following plates the figures representing the size of the specimens should be somewhat reduced.

Proc. Yorks. Geol. Soc., Vol. XVI., Plate X.

and bluish, rather hard and splintery. They contained goodsized oysters, numbers of small bivalves, and other shells; also many Ammonites, all crushed excepting those in the calcareous pyritous nodules, which were better preserved and large, often more than a foot across. These Ammonites belong to a form of Hoplites apparently distinct from those above-mentioned.

The lower half of a Belemnite, found a little below the band of nodular material, afforded the only indication of the existence of that fossil at this horizon. The fragment, together with the impression left by the vanished part of the guard, showed that this Belemnite was of the Porrectus type, but proportionately shorter, and not the Bel. troslayanus found by Mr. Herries.

Another exposure at a presumably higher level seemed nearly devoid of all fossils except Ammonites of the Perisphinctes type-P. lacertosus, Dum. et Font. These, like the Hoplites, were much crushed, often large, and fairly well preserved only in the nodules. It is hard to say what position the beds of these isolated exposures occupy in relation to those described by Leckenby, but if this Perisphinctes corresponds to Ammbiplex they probably form part of his lowest series No. 1.

In most of the much higher beds crushed Ammonites abound, and in some near the top they occur as soft and brittle yellowish casts, indistinctly appearing to belong to roundbacked forms. I have also seen detached nodules crowded with a species much resembling the figure of Olc. (Perisphinctes) cf. miatchkoviensis in the "Argiles de Speeton,” Pl. I., fig. 6.

ZONE E (COPROLITE BED).

In the medley of materials that form this seam there are many Ammonite fragments, among which Prof. Pavlow recognised Olc. (Virgitates) cf. scythicus Michal., Olc. (—) cf. Tchernischowi Michal., Olc. (-) cf. Panderi d'Orb, and Olc. (-) cf. dorsoplanus Michal.