The unstratified rocks of Sky are trap and syenite; and to them no very distinct position can be assigned, because, though they often appear as if capping or overtopping the superior strata, it is also manifest that they occasionally penetrate through them. Dr. M'C. observes:

In commencing the account of these rocks, the trap * and the syenite, I must premise that I have not found in Sky any indication to denote the relative order of the two. If indeed they are both irregular substances, as I think there is no reason to doubt, any priority or posteriority is out of the question, or at least it cannot be ascertained by examining their juxta-positions. If the one set were proved to be constantly superior to one set of stratified rocks, and the other to a different and later set, the question of rank might be settled between them: but these connections are difficult to ascertain to a sufficient extent, and possibly none such exist. If one stratified rock is in one place superior to another, we are sure that it is every where superior; but if we have ever so clearly proved that a body of trap or of any other unstratified rock is superior and in contact in one place to any given stratum, we have no certainty that it is equally so every where. Thus I shall in this island show that the trap rests in one place on the latest sand-stone, in another on the earliest. No means therefore are offered here of determining the relative order of these two unstratified rocks, but I have little doubt from the phenomena which I have witnessed in Rum and Mull, that they are both portions of one irregular mass.'

The unstratified or mountain-trap of the Cuchullin hills passes, without discontinuity, into the stratified, which forms by far the greater portion of the surface of Sky; and it is

• * I think it necessary to say that I have throughout used the term Trap as the name of a family, including basalt, green-stone, tuff, amygdaloid, trap-porphyry, and many other varieties of rock which have as yet obtained no names, and which constitute a class equally distinguished by their geological as by their mineral characters. I have preferred it because, as it is derived from the external outline so common and characteristic of this class of rocks, it is in no danger of misleading by producing any confusion of individuals, and because it was already in use as the name of many in this family without having been rigidly limited to any one species. I have also chosen the term Syenite as the generic term of a set of rocks generally allied to these, and which had already been applied to that rock by Werner; excluding from this denomination the original and classical syenite, which as well in geological connection as in mineral character is a mere modification of granite. The compound term syenitic granite may be applied to this, as I have remarked in a former paper. Varieties intermediate between common trap and syenite may be called syenitic trap.'

highly worthy of remark that it manifests, in different places, all the hypothetical characters that have been assigned to the primitive, transition, and flotz-traps. Among the numerous varieties of the trap-family here specified, basalt is the most conspicuous, and it occurs almost every where; alternating, in an irregular manner, with all the other varieties. It is most frequently amorphous, and sometimes perfectly black, and of a very fine grain. The amygdaloidal sorts are also common, of various colours, of very different degrees of hardness, and including nodules of zeolite, calcareous spar, chlorite, steatite, quartz, chert, chalcedony, and prehnite. Trap-tuff, or, as the author more correctly denominates it, trap-conglomerate, is sufficiently common: but green-stone and green-stoneporphyry are less abundant. To these members of the trapfamily are added, by way of supplement, iron clay, coal, in small quantities, siliceous schist, and a particular sort of jasper, which is yellow, or brown, with a lustre approaching to resinous, and perfectly analogous to a similar production from the island of St. Helena, which has been improperly classed with the pitch-stones. Specimens of the same substance have been found in Guadaloupe, where they occur among the lavas of that island, adding one more to the numerous analogies already existing between the volcanic rocks and the trapfamily.' The unstratified traps of this island present the external features of granite, though they differ from it in composition; consisting of green-stones of various structure and complexions, and clink-stone of several modifications.

In close connection with these substances is the syenite, similar to that which is found with the trap-formation in the isle of Arran. Its basis, which generally passes for felspar, may in its soft state be regarded as a clay-stone, and, in other stages of induration, as clink-stone, or compact felspar. In colour, it varies from ochrey yellow and dirty flesh-colour to gray. Though often cavernous, and impregnated with ferruginous clay in other situations, it contains crystals of felspar, and thus constitutes various kinds of porphyry: but its predominant form, from which its name is derived, is an aggregate of felspar and hornblend, in which the latter generally bears a very small proportion to the first.

Dr. M'C. has entered into some very interesting details relative to the numerous trap-veins that are observable in the island. Their prevailing material is basalt; and they consist of two distinct sets, which hold their course through one another in every direction. The angle of their courses with the horizon is various, but in a very considerable proportion it is vertical, or nearly so. At Strathaird, in consequence of their

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their frequency, when collectively measured they nearly equal in some places the stratified rock through which they pass. Here it is stated that they produce no symptoms of the slightest disturbance having taken place in the evenness of the sand-stone strata which they intersect.

The Doctor commences his descriptive catalogue of the more remarkable minerals which he had occasion to observe, in the course of his survey, with the different kinds of zeolite, some of which occur in great profusion. Analcime, chabasite, and stilbite, (the last in enormous quantities,) all pass in review. Mesotype occurs in the compact, mealy, and crystallized form. Prehnite and epidote are both found in some of the trap-rocks, though in trifling quantities.

The last and the rarest mineral which I discovered in Sky is hypersthene. This occurs at Scavig, in that singular variety of trap which I have already described in the account I gave of the Cuchullin hills: it forms veins of different dimensions and much blended with the rock in which they lie, but they are neither numerous nor large, nor are the veins simple in their composition, since they resemble the containing rocks in the different substances of which they are composed. The most prevailing mixture is however that of hypersthene, and of a dark felspar precisely resembling that of Labrador in its general aspect, but not possessing its iridescence. This felspar is frequently crystallized, but, as the crystals are always completely imbedded, nothing further of their form can be discovered than the outline which is displayed by the fracture; together with the dark felspar, white and glassy felspar also occurs in the mixture, and the common opake white variety is sometimes, but more rarely, intermixed with all the other substances.'

The hypersthene presents specimens of great magnitude and beauty, which, although they seem to resist the injuries of time far longer than the accompanying substances, at length also become rotten, and fall into an ochrey powder. Distinct concretions are to be found exhibiting the primitive form, and which appear to be true crystals, since they are detached from the surrounding substances. More generally, however, it is without form, while in many cases it is intermixed with the dark felspar so as to present the graphic character, the crystals of felspar being defined, and the hypersthene occupying the interstices. The lustre of this mineral is always highly metallic, but the specific gravity of the specimens which I examined did not exceed 3.342. The colour is various; in general it is of a purplish black, sometimes steel gray, and more rarely of a pale whitish gray, while it often assumes the hue together with the lustre of polished brass, when it has long been exposed to the air.

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Hypersthene has been found in Aberdeenshire, but the circumstances which accompany it have not been described, nor the nature of its connections ascertained. As far as can be deter

mined by this instance, it must be considered as an inmate of the trap-family. Having also found it in the island of Rum associated with the same class of rocks, additional confirmation is afforded of this connection. That of Labrador is known, like the present, to be accompanied by dark felspar; but the rock which is the common repository of both has not been described by the missionaries, to whom we are indebted for the only knowledge we possess of that country. Mr. Giesckè considers the Labrador felspar of Greenland as belonging to what he calls the "syenite-formation," and it is not improbable that his syenite-formation resembles the rock which I have already described, and that there is a correspondence in the repositories of this substance in both countries.

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Among the rocks, for which I could not find a place in the geological description without disturbing its order, pitchstone requires to be noticed. Although not found in situ, it offers as a mineral specimen some appearances which are interesting, and which I shall therefore describe. It was on the hill of Glamich that I found the specimens in question, and it is probable that they had been detached from some veins which I was unable to trace. There are two varieties, a black one very little differing from that of Rum, except that it contains a few dispersed crystals of glassy felspar; and an olive-green one, which, as it offers some apparently important peculiarities hitherto unobserved, I shall describe more fully. It is often of a granular combined with a small conchoidal fracture, and is generally disposed in distinct concretions which are either of the flat or curved lamellar form. It is remarkable for containing irregular rounded cavities similar to those of the amygdaloids, filled with compact grains of a grayish hue. The structure of these is so singular as to be deserving of notice. On breaking the smaller ones, they are discovered to consist of a grayish white enamel, similar to that which is formed by the fusion of felspar. But if we break the longer grains we can distinctly see that the center is composed of glassy felspar, the crystalline transparency and platy fracture of which are perfect, while the surface to a certain depth is converted into the white enamel I have described. I have not observed this very peculiar and striking appearance in any other pitchstone which has come under my notice, although there are appearances not much unlike it in some of the varieties found in Arran.

Those who conceive pitchstone, like basalt, to be of igneous origin, will have little difficulty in explaining this phenomenon, and will even find in it strong evidence to support that theory. It is unnecessary to enter on a reasoning so obvious.'

The variations of the magnetic needle, produced by a large portion of the summit of Glamich, form another topic, which Dr. Mac Culloch has treated with his accustomed ability: but. they are represented more distinctly in the diagram than they can be described by words. Moreover, we can no longer refrain from imposing on ourselves a painful act of self-denial, by taking leave, for the present, of this instructive guide through

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through a stormy island, which has been rarely explored by men of science. We shall not, therefore, attempt to put our readers in possession of his excellent remarks on the scanty appearances of coal which he had occasion to notice, on the geological history of the Lydian stone, and on his sagacious comments on statuary marbles, with a particular reference to those of Sky. This paper is well illustrated by a geognostic map of the island, and by sections of the strata and veins that are described. The writer, however, never once alludes to a previous examination of the same island by Professor Jameson, of Edinburgh; a circumstance which is the more to be regretted, because the statements of these two geologists are sometimes at variance. Thus, Mr. Jameson makes repeated mention of wacke as occuring in large quantities, whereas Dr. Mac Culloch expressly says, wacke is, I believe, totally unknown in this island. In such cases, the discrepancy may sometimes be resolved by mutual explanation, and an exchange of definitions of terms.

On the Oxyd of Uranium, the Production of Cornwall, together with a Description and Series of its Crystalline Forms. By William Phillips, Member of the Geological Society.The few crystalline modifications of this rare mineral are here distinctly defined, and exemplified by figures.

On the Geological Features of the North-eastern Counties of Ireland, extracted from the Notes of J. F. Berger, M.D. M.G.S. With an Introduction and Remarks, by the Rev. W. Conybeare, Member of the Geological Society. Mr. Conybeare's Introduction comprizes a rapid geological view, first, of the Mourne Mountains, in which the exterior transitionchains extend greatly beyond the primitive nucleus of granite and hornblend rock; secondly, of the Primitive Chain of Londonderry, consisting chiefly of mica-slate; and, thirdly, of the Basaltic Groupe. These divisions of the district to which Dr. Berger's observations refer, it is alleged, may correspond respectively with the transition, Grampian, and trap-chains of Scotland, of which they may be only continuations. the same time, this hard union between the two islands would require to be established on more minute and satisfactory evidence than its ingenious advocate could, with propriety, introduce into this summary sketch.

At

With regard to Dr. Berger, he dissects his appropriate field more in detail, and investigates the prevailing rocks under the fourfold division of Primitive, Transition, Flatzrock, and Floetz-trap. Without demurring, at present, to the accuracy of this partition of his subject, we shall only beg leave to observe that the members of each section, and their

general