former occasions with respect to the geographical distribution of the marine fauna of Europe. A yachting excursion which he had taken in the course of this summer, accompanied by two scientific friends, to the northernmost part of the British Isles, together with an examination of the upper tertiaries in Suffolk and Norfolk which he had since made in company with Mr. Prestwich, gave the author a better insight into the scope of such distribution than had resulted from his previous researches, and confirmed his belief that the division into separate areas or "provinces," which had been proposed by so many systematists (all of whom held different opinions as to the extent and limits of such "provinces "), was erroneous, and that the present distribution must be referred to a state of things which has indeed passed away, but left a very distinct impress of its action. The author is inclined to take the Coralline Crag as a starting-point, and to consider the marine fauna of Europe, Northern Asia, the Cis-Atlantic zone of Africa, and part of North America, as having been closely related at a comparatively recent epoch, and as forming one common area of origin. Many species of Mollusca once existed at both extremities of this vast district-e. g. Mya truncata and Buccinum undatum; and other species hitherto supposed to be restricted to the Mediterranean (viz. Monodonta limbata and Cerithium vulgatum, with its variety C. calabrum) have lately been discovered by Professor Sars on the coasts of Finmark. It is also probable that the recent exploration of the Greenland seas by Otto Torell and others may reveal further instances of a similar kind. Very little has hitherto been done towards the investigation of the Arctic fauna. It by no means follows that an extremely rigorous or "arctic" temperature prevailed in those places where we find the remains of some Mollusca which now inhabit only the seas of colder regions, or, vice versa, that the presence in these regions of fossil shells belonging to species which now inhabit only more southern seas indicates the former prevalence of a warm climate. The temperature of the sea at certain depths is well known to be very equable; and it is only littoral or shallow-water species that would be exterminated or affected by a change of climate. Some kinds appear to be more hardy than others, and to have survived considerable and perhaps frequent changes of temperature; while others have undergone a limited modification of form, and are considered by some naturalists as distinct (or "representative") species. A great deal, however, yet remains to be done, by accumulating facts, and a critical comparison of recent with fossil species, before a complete or satisfactory theory of distribution can be established.

Mr. Jeffreys contrasted his experience of this dredging expedition with those he had made to other parts of the British coasts as well as to the Mediterranean, and also with the accounts he had received of similar expe ditions to the coasts of Norway and Sweden-showing the far greater difficulties which attended an exploration of our northernmost sea, by reason of the variable and often tempestuous weather, and of that line of coast being unsheltered from the prevailing winds. He, however, succeeded in procuring three species of Mollusca new to science, which he proposed to name Margarita elegantula, Aclis Walleri, and Nassa? Haliaëti, besides twelve other species which were new to the British Isles. Of these last, ten are Scandinavian, one is Mediterranean, and the other had hitherto been known only as a Crag fossil. He reserved the description and particulars of these species for a work on British Conchology which he had undertaken. He ascertained that the Gulf-stream never impinges on any part of the coast which he had examined, although the climate was temperate.

The author noticed the occurrence at considerable depths (nearly 80

fathoms) of living Mollusca which usually inhabit the shore or very shallow water, viz. Lamellaria perspicua, Nassa incrassata, and Cypræa Europæa, all of them being widely diffused species, thus apparently illustrating the view entertained by the late Professor Edward Forbes, that those species which have the widest horizontal range have the greatest vertical depth. Judging, however, from the great depth at which he found the fossil shells of some Mollusca (e.g. Pecten Islandicus and Mya truncata var. Uddeval lensis) which inhabit much shallower water in the Arctic zone, the author is disposed to believe that the bed of this part of our Northern Sea has sunk since the so-called "glacial" epoch, and that this circumstance may possibly account for the above-mentioned occurrence of sublittoral species at such depths.

With respect to the comparative size of those Mollusca which are common to the seas of the North as well as of the South of Europe, the author referred to an observation made by Mr. Salter, in a recent number of the 'Quarterly Journal of the Geological Society,' that some fossil shells which Mr. Lamont had brought from Spitzbergen were larger than those of the corresponding species in our own mountain limestone; and he remarked that the same rule appears to apply also to marine plants, for he never saw such gigantic fronds of the Laminaria saccharina, which fringes all our coast. line, as he did in the voes of North Zetland.

The author concluded by paying a just tribute of respect to the labours of Professors Sars and Lovén, Malm, Mörch, Asbjörnsen, and other Scandinavian naturalists, who were investigating the Mollusca of the Northern seas with a zeal and accuracy worthy of our emulation.

Contributions to a Report on the Physical Aspect of the Moon. By J. PHILLIPS, M.A., LL.D., F.R.S., Professor of Geology, Oxford. PROFESSOR PHILLIPS noticed the result of his sketches of parts of the surface of the moon, and also described Mr. Birt's contributions to a report on selenography, which had been undertaken by direction of the General Committee at Oxford, with the view of discovering the character of the moon's surface as influenced by previous physical events. Professor Phillips's observations related especially to the mountain Gassendi, to which his attention had been directed by the Committee in 1852, but included also drawings of remarkable 'rills,' and other interesting peculiarities, in Aristarchus, Archimedes, and Plato.

The rills to which Prof. Phillips had given principal attention were-(1) the well-known stag's-horn rill E. of Thebit, which appeared to be what geologists call a 'fault' or 'slip,' one side elevated above the other, and with some inequality in the dislocation when the shadow is accurately inspected; (2) the long rill on which the small crater called Hyginus is situated; (3) the group of parallel rills about Campanus and Hippalus. Regarding these it was remarked that the drawing of Mädler, which, like all the work in his great map, was obviously a careful one, differed in one point from that made by Prof. Phillips. This difference may be thus stated. In Mädler's drawing three parallel rills appear in the space between Campanus and Hippalus; the middle one, shorter than the others, passes between two small hills. Prof. Phillips draws these two hills near to each other, and records no rill running between them. The rill between these hills and Hippalus appears in

both drawings; but Prof. Phillips continues it further to the south, even into the crater marked A, which is likewise traversed by the longest rill of all, that, viz., nearest to Campanus. Another rill is traced by Prof. Phillips quite across and through the old crater of Hippalus; and all the rills appear to him to be rifts or deep fissures, receiving strong shadows from oblique light, and even acquiring brightness on one edge of the cavity. Their breadth appears to be only a few hundred feet or yards. He exhibited drawings of these objects on a large scale, one being a section across the crater of Gassendi, another a map of the curious region extending from Aristarchus and Herodotus along the interrupted rift or valley which opens by a seeming delta into the seeming dried sea-bed with indented coasts on the south.

Speaking of Gassendi, of which he had made drawings under different conditions of light and shade, from sunrise on the mountains to mid-day, and slighter sketches at later hours, he remarked, in addition to what has been recorded by Mädler, the much-varied character of the 'rings,' the deep narrow fissures across the ring on the S.E. side, the rocky character of the central elevations in the interior area, the rough terraces and ridges within the great ring on the east and also the north-west side, the occurrence of only two small craters in the northern part of the area, and the variation of colour on the surface, without shadow, according to the change of the angle of incidence of the sun's rays.

He also drew attention to the existence of delicate ramifications of small ridges and hollows in the S.W. part of the area, which had a marked convergence towards the broad lip of the deep-attached cavity known as the Spoon. He expressed his great desire to receive drawings of Gassendi as seen at noon and at later hours of the lunar day.

Contribution to a Report on the Physical Aspect of the Moon.
By W. R. BIRT, F.R.A.S.

Os the present occasion I propose confining my contribution to the physical features characterizing the well-known spot Plato, some of which are familiar to astronomers, while others, I have some reason to believe, have not hitherto been pointed out. I have included all that have come under observation during the twenty-nine months between January 1860 and May 1862, inclusive, in a synopsis of objects suitable for further telescopic observation. This synopsis of objects is necessarily incomplete. To each object observed I have appended, in italics, the number of times it has been the subject of special observation; so that every one inserted in the key-plan has been seen by me at some time during the interval of the observations above mentioned. The entire period of the visibility of Plato is embraced in the observations, which are, however, more numerous under the morning and mid-day illuminations than under the evening. Those features that have been more frequently observed may of course be regarded as being more fully established, at least for the period embraced by the observations; the synopsis forming a groundwork for the more effectual observation of Plato, especially as regards the interesting questions of absolute repose now existing on the moon's surface, or the progress of change such as may be detected by human eyes. Forty-five series of observations contributing to the synopsis, and extending from January 5, 1860, to July 29, 1861, I have arranged in the order of the moon's age, in a MS. volume which is deposited in the library of the Royal

Astronomical Society. The remainder, twenty-three, bringing the observations to May 12, 1862, are at present in my hands, and are intended to form part of a second volume, should I be able to pursue the observations. The arrangement of the volume is such that it can be used as an ephemeris of the successive appearances of the crater, as well as being indicative of those objects that require careful and steady watching.

One of the most interesting objects among those newly pointed out is a terrace on the south-west interior slope. It, with a ravine in the same neighbourhood, is of an exceedingly delicate character, being brought out (especially the terrace) by the gradual change in the direction of the incident solar

ray.

Accompanying the synopsis are two illustrative figures. Fig. 1 is a somewhat rough key-plan of the crater, the ellipse being that of the greatest opening presented by Plato. This key-plan possesses no pretensions either to accuracy of detail or correctness of locality, micrometrically considered; it is only offered as a guide to the general and relative positions of the objects included in the synopsis. Fig. 2 is a section indicated by observation of the south-west interior slope of Plato, showing the terrace or ledge Y, one of the new features brought to light by this series of observations. The reader is referred to Beer and Mädler's large map of the moon, and is specially requested to compare the delineation of the crater as they have given it with the keyplan accompanying this Report. A careful comparison of them will show the features they have in common, and the departures that may exist in those determined by the present series of observations from the representations of the same features as given by Beer and Mädler. Schröter has given some of the features mentioned, especially the mountain-range (n), which he marks μ, the mountain v, the shadows of the three peaks y, d, and e, the mountain c, which in Schröter's drawing is marked D, and the crater x, which is no longer in existence-if Schröter really saw a perfect crater as he has delineated it. In another delineation of Plato by Schröter, showing the two markings i and k on the interior of the north-east slope as he observed them on December 11, 1788, he also gives a remarkably round cloud-like appearance, not unlike in character to the one that has been so constantly a subject of my own observation, marked ƒ in the key-plan. These delineations may be found in his 'Selenotopographische Fragmente,' t. xxi.

To render the results of the inquiry of greater value, a careful micrometrical survey of Plato, when presented under the greatest visual angle, would be important. Every well-determined spot would be laid down in its accurate position as seen from the earth under that angle; and if such a survey were executed with the requisite precision, one epoch only being fixed on, and no reduction to a mean state of libration admitted, it would not be difficult, after a few years' observations, to judge of the probable fixity of aspect presented by the most prominent features, and changes, if any, would soon render themselves apparent.

Synopsis of objects in Plato suitable for telescopic observation, with reference to fixity or variability of absolute aspect.

By absolute aspect, I mean the aspect dependent on the object itself, its form and constitution,-not an aspect dependent on the variability of the incidence of solar light, or on the variability of the direction of the visual ray as the object is seen from the earth, the one indicated by the moon's age, the other by the libration of the moon.

Key-plan of Plato, from observations by W. R. Birt, F.R.A.S., between January 5, 1860, and October 19, 1861.

I. n. A short range of mountains running at first nearly at right angles to the mountainous rim of Plato, from a break in the northern or, rather, north-western portion of the rim. This range of mountains is of a curved form, and terminates in the mountain. It constitutes the western rim of a crateriform formation to the north of Plato.

This mountain-range has been the subject of eleven observations between January 1860 and May 1862. Schröter had previously observed it, and marked it μ. Under a suitable illumination, a shallow depression is scen westward of this mountain-range, the land rising a little on the westward of it, so that a somewhat narrow valley is enclosed between the two. There are two well-defined peaks on the eastern or highest range, and a small one between them and the rim.

II. 1.-A break on the north-western rim of Plato, which is doubtless the continuation of the narrow valley west of the mountain-range (n). It is distant about 075 of the longest diameter of the apparent ellipse from the east, and is very distinctly shown in the drawing of Schröter.

The observations of this break in the rim of Plato have been numerous. On three occasions the valley-like character of it has been recorded. Under a suitable illumination, a bright streak from Anaxagoras to Plato may be seen terminating near this break.

III. m.-A bright spot on the north-west portion of the rim, close to and east of the valley (1). On the 28th of May, 1860, I have recorded a high alpine mountain in the locality of this spot.

This bright spot has been observed on nine occasions, and on one occasion as a dusky spot.

IV. The interior slope of the north and north-east border. This slope undergoes variations of luminosity, according as the incidence of the solar rays vary; it has two dark oval markings.

V. 2.—Under a somewhat late illumination, 21.5 days moon's age, the rim of this part of Plato presents the appearance of a sharp angle in the neighbourhood of the westernmost of the two oval markings, and from this point an irregularly formed crag overhangs the slope. This crag has also been seen under the morning illumination.

There are strong indications of a circular range of mountains existing on the north of Plato, of which the range (n) forms the western side: the included area is crossed by two dark but narrow lines, which appear to be of