534 Henry B. Brady—Notes on . favour of the rock being regarded as chalk are that physically it is almost indistinguishable from most typical specimens of that rock, and that it has had the same organic origin; the Foraminifera alone are not, unfortunately, sufficient to rigidly determine the geological age of the rock, because they are types which have been persistent from the Cretaceous period to the present time.

II.—SUPPLEMENTARY NOTE ON THE FORAMINIFERA OF THE CHALK (?) OP THE NEW BRITAIN GROUP. By HENRY B. BBADY, F.R.S., ETC., ETC. INCE writing the letter quoted in the foregoing communication S by my friend Prof. Liversidge, I have had the opportunity of examining a larger fragment of the rock to which it refers, and am thereby enabled to add somewhat, not merely to the list of Foraminifera which it contains, but also to the general con- clusions to be drawn from it. The lithological characters of the rock are, as Prof. Liversidge has stated, precisely those of many specimens of chalk, but it is seldom that a Cretaceous mineral is so entirely composed of the recognizable remains of microzoa, and it is still more rarely that a geological deposit occurs, for which so exact a counterpart in process of formation can be indicated. Under these circumstances some further remarks on the subject may not be without interest. The following is a revised list of the Foraminifera, with notes appended concerning a few of the less generally understood species : Spiroloculina eelata, Costa. Globigerina bulloides, d'Orbigny. Lagena marginata, Montagu. inflata, d'Orbigny. lievis, Montagu. Duterlrei, d'Orbigny. apiculata, Keuss. sacculifera, nov. aspera, Eeuss. (Orbulina) univeisa,d'Orbigny.1 Denlalina brevis, d'Orbigny. Sph

Downloaded from https://www.cambridge.org/core. Newcastle University, on 20 Jul 2017 at 12:08:56, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800150137 Henry B. Brady—Notes on Cretaceous Foraminifera. 535 Quinqneloculina agglutinans of d'Orbigny both in shell-texture and in general contour. The late Professor Costa figures such a form (Paleont. del. Eegno di Napoli, pt. 2, pi. 26, fig. o), though in some- what clumsy fashion, under the name above employed. Lagena marginata.—Two or three pretty distinct forms are in- cluded under this specific name. The varieties of L. marginata have not as yet been sufficiently worked out. Globigerina sacculifera, nov.—This is a somewhat important modi- fication of the Globigerine type, and one that appears almost to have escaped attention hitherto. Dr. Carpenter figures a poor specimen (' Introduction,' pi. 12, fig. 11) under the name Globigerina helicina, d'Orb., but the figures in Soldani's ' Testaceographia,' on which d'Orbigny founded that species, pertain to a very different form, the name for which cannot be spared. Reserving details respecting the subordinate groups into which the genus may be divided for another opportunity, it will suffice to state here that the trivial name sacculifera has been applied to a set of Globigerince, in which the terminal chamber or chambers take an elongate, pouch-shaped and usually pointed contour, and always present at least one large aperture on the superior or spiral surface. Such forms are common and grow to considerable size, especially in deep water south of the Equator. Pulvinulina Menardii, var. tumida, nov.—A thick, oblong modifica- tion of P. Menardii, d'Orb. The superior surface is subconical, the inferior strongly convex. There seems to be no satisfactory descrip- tion or figure of this variety, though the dead shells are common, and of large size, in many deep-sea dredgings. Pulvinulina favus,-noY., is a somewhat remarkable species. When fully grown, the test is lenticular, and nearly symmetrically bi- convex, and the surface, except around the aperture, which is oblique, and peripheral, is covered with a raised reticulate ornamentation. The spiral structure is entirely concealed by the exogenous honey- comb-like shelly deposit. Young specimens are relatively much thicker than adults, and have the margin blunt or rounded. Comparing the Ehizopod fauna characterized by the species above enumerated with what we know of the accumulations at present going on at the sea-bottom in various parts of the globe, it is not difficult to indicate recent deposits at depths of 1400 fathoms and upwards in either the Atlantic or the Pacific having the same general characters in their organic constituents. There is, however, one species, Pulvinulina favus, which serves to limit the area of com- parison. A cursory examination of the rough notes upon about a hundred and fifty soundings from the " Challenger " and " Porcu- pine " expeditions has only furnished six localities at which this form occurs, and these are all of them between Stations 271 and 302 of the " Challenger" series, that is, from just on the Equator in the middle of the Pacific, on a course direct south and then east, to a point off the South American coast, lat. 42° 43' S., long. 82° 11' W., the depths varying from 1375 faths. to 2435 faths. Upon closer

Downloaded from https://www.cambridge.org/core. Newcastle University, on 20 Jul 2017 at 12:08:56, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800150137 536 S. V. Wood,jun.—American and British Surface-Geology. comparison it is noticeable that the soundings obtained from this area also resemble the rock under examination in the comparative rarity of Pulvinulina Mieheliniana, one of the commonest of Atlantic Foraminifera, and in the scarcity of the arenaceous types. But little care was taken, in the process of washing, to preserve the Radiolaria, but such as remain are of the same species as those of the line of dredgings alluded to. In conclusion, it appears to me not too much to say that after disintegration and washing this " Chalk" from the New Britain Group could not possibly be distinguished by its organic remains from a washed Globigerina-ooze dredged in 1500 to 2500 fathoms in the South Pacific. The determination of the exact geological age is a matter for geologists; my observations have necessarily been limited to the physical characters and the organic constituents of the specimen placed in my hands by Prof. Liversidge, but it appears worth considering whether the rock may not be part of a recent sea- bottom which has been distributed by volcanic or other agency. Such deposits may be very old chronologically speaking, and we know by dredging experience that they do often become very hard and compact even comparatively near the shore. Mr. Brown's letter, quoted above, provides us with the required disintegrating force.

III.—AMERICAN " SURFACE GEOLOGY," AND ITS RELATION TO BRITISH. WITH SOME REMARKS ON THE GLACIAL CONDITIONS IN BRITAIN, ESPECIALLY IN REFERENCE TO THE " GREAT ICE AGE " OF MR. JAMES GEIKIE. By SEARLES V. "WOOD, Jun., F.G.S. (PART II.) {Continued from page 496.) •VTUMEROTJS buried channels filled with drift occur over Ohio and X\ the neighbouring states forming the St. Lawrence basin. Some of these penetrate the water-parting, and formed, according to Prof. Newberry, waste weirs through which the lake waters of the St. Lawrence basin escaped into the valley of the Mississippi, as the land rose and the sea retired from that valley. This, if I understand him rightly, took place after the beds 3a had been formed, and before the terraces, to be described under the number 4, began to form by the fall of the lake waters; but these waste weirs would seem to have probably acted the same part also at an earlier period, viz. during the commencement of the Erie clay deposit, when the lake began to form by the recession of the ice from the water-parting, and when it must have been full up to the brim of that parting, or at least up to the level of the waste weirs. The final shrinking, however, of the waters of the lake-basin is marked, according to Prof. Newberry, by the formation of clearly- marked terraces or lake-beaches at successive levels, the uppermost of which inosculates with these waste weirs. The shrinkage giving rise to them may have arisen, he says, from the removal of ice-dams

Downloaded from https://www.cambridge.org/core. Newcastle University, on 20 Jul 2017 at 12:08:56, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756800150137