Billeder på siden

accomplished, we sat down to supper, and c'en made the most of our fish in the dark.'

On the subject of emigration, it appears to be the decided opinion of the author, that no part of America equals the vici. nity of Montreal in Canada, for an English or Irish settler; there he will find himself surrounded by his countrymen ; and there he will still see ample room for thousands of addin tional inhabitants. [To be continued.]


Art. II, An Outline of the Mineralogy of the Shetland Islands, and of
the Island of Arran. Illustrated with Copper. Płates. With an
Appendix, containing Observations on Peat, Kelp, and Coal.
By Robert Jameson, Member of the Royal Medical, and Natural
History Societies, Edinburgh. 8vo. 78. in Boards. Cadell
jun. and Davies. 1798.
NATURAL History comprehends so many useful branches of

science, and affords such interesting sources of instruction, that it has in all ages claimed our highest regard. The labours of the immortal Linné cleared the path, which led to the accurate discrimination of the products of the animal and vegetable kingdoms. His illustrious countrymen, Croosted and Bergman, have done much towards the arrangement and description of the mineral kingdom : but the industry and genius of Werner have been successful beyond all his predecessors in mineralogy. Mr. Kirwan, by the publication of the second edition of his book on that subject, has presented to the English reader an accurate and pretry full account of the Wernerian characters, sind has also given the only complete description of mineral productions which ever appeared in Great Britain, As three

years have scarcely elapsed sinee the publication of Mr. Kirwan's performance, it is not surprizing that few accurate mineralogical works have here been effected; a matter much to be Jamented, when we consider the importance of the science, and the wide field hitherto unexplored in this country. Scotland abounds in rocks and minerals, and therefore well deserves the attention of the geologist and mineralogist. The book now before us (which is unquestionably the first regular piece of Scottish mineralogy) is a proof of our statement. It opens with a short introduction, written in a style of much modesty: but, after having perused the subsequent pages, the reader is in duced to set a higher value on Mr. Jameson's abilities as a mi. neralogist, than he seems to do himself.. Indeed, the work bears undoubted marks of active and successful research. Mr. Jameson is perspicuous in his arrangement, concise in his description, and his strictures on many articles of the Huttonian system are extremely sensible.


The account of the Shetland islands, which forms the first part of this Outline, is manifestly less complete than the description of Arran: yet it relates many interesting mineralo. gical facts.

The first chapter contains a few observations on the general appearance of the country, the westerly elevation of the mountains, climate, &c.

The following remarks give a' striking view of these secluded islands :

• On viewing these islands in general, a wonderful scene of rugged, bleak, and barren rocks presents itself to our view. No tree or shrub is to be seen to relieve the eye in wandering over these dreary scenes. Sometimes, however, a few scanty portions of cultivated ground catch the eye of the traveller, exciting emotions of pleasure, and forming a striking contrast to the barien heath-covered mountains which skirt them. The western part presents many scenes, as wild and sterile as can well be conceived; grey rocks, rising froin the midst of marshes or pools, and shores bounded by awful scabcat precipices, do not fail to raise in the mind ideas of desolation and danger. The coasts are in general rugged and precipitous; present. ing in many places, scenes truly grand and magnificent; vast rocks of various heights, dreadfully rugged and broken, opposing their rude fronts to all the fury of a tempestuous ocean: which has in some places formed great detached pillars, in others has excavated grand natural arches and caverns, that mock all human magnificence, and strike the beholder with that awe and wonder, which must affect every one on viewing these amazing wrecks of nature.'

• The weather is extremely variable, being much incommoded with rains and thick fogs; which occasion many vessels to be wrecked on these terrible shores. During the winter there are considerable falls of snow, which lies but a short time, on account of the vicinity of the sea. The frosts, which are seldom severe, and never long, produce little inconvenience ; but were they to continue for any considerable length of time, it would be heaping horror upon horror, and would render a situation already dreary,comfortless. Frequently, during the winter, dreadful storms prevail ; particularly from the west ; which are accompanied with thunder and lightning ; an appearance seldom observed at that season in other parts of Britain. The aurora borealis (or what are usually called strcamers) illuminate the sky with uncommon brilliancy, and help greatly to alleviate the gloom of the long winter nights.'

The second chapter comprehends the mineralogy of the Main-land, which is the largest of the Shetland islands. The descriptions here, as in other parts of the volume, are carried on nearly in the journal form; which the author deems best suited to the view that he designs to give. Mr. Jameson appears to have traced the strata round a considerable partof the island; and these he finds to be composed of micaceous shistus, granite, gneiss, chlorite-shistus, sand-stone, and lime-stone. By the decom

position position of the sandstone and micaceous rocks, great quantities of sand are formed, which become very destructive to the neighbouring land. Thus, Mr. Jameson remarks :

• Below us we have a direful example of the blowing of loose sand, or what is called the sand-flood; for an estate, which belongs to Sinclair of Brue, is now rendered a forlorn waste, although, before this calamity, it was one of the most productive parts of the island. I could not learn the cause of this disaster, but it was probably owing to the tearing up of some of the plants which are known to prevent the blowing of sand. This practice cannot be too severely reprobated, when it is known that the consequences are so pernicious ; thus, in many of the western islands, Dr. Walker has observed, that if the smallest aperture be made in the sand, the food instantly commences : and we know that in Suffolk, a quantity of sand, which at first covered only ten acres, has now spread itself, and covers several thousand. The sowing of plants, which grow in loose sand, is the only remedy which can be recommended to stop the baneful progress of those floods, and of these several have been recommended; but the most efficacious are the Galium luteum, Elymus arenarius, Triticum junceum, and Arundo areraria; this last, the Dutch plant with great benefit.'

The third chapter is occupied with the mineralogy of the islands of Foula, Papa-Stour, &c. ; in the course of which, many valuable remarks occur: but they do not admit of abridgment.

The fourth chapter contains the mineralogy of the North isles of Shetland. The island of Unst, one of the most considerable of them, contains serpentine, gneiss, micaceous shistus, ardesia, sandstone, and limestone. In this serpentine, several curious fossils occur: of which Mr. Jameson describes particularly the following: 1. Lamillar. Actynolite; 2. Labrador Horneblende ; 3. Tremolite ; 4. Shistose Talc.-- In the island of Fetlar, where the serpentive again occurs, a species of micaceous shistus is found, similar to that which was observed by Saussure, at Valorzine, in the Alps. - In the island of Yell, several veins of granite are to be observed, traversing the micaceous shistus ; and similar to those which have been described by Saussure in his travels, and by Werner in his book on the formation of veins.

The mineralogy of the island of Arran is comprised in six chapters, which contain a variety of interesting matter, but so closely connected, that we find it difficult to give a view of the whole, without entering into a very copious detail. We shall therefore rest satisfied with two extracts : one to shew the manner in which the author conducts his geological investigations; the other as a specimen of his description of particular fossils. Previously, however, we may remark that Mr. Jame


son appears, in his account of Arran, to have altered his are rangement by separating the geological observations and mineralogical descriptions from each other. We think that this mode of treating the subject is extremely proper; and had the celebrated Reuss, and other .German writers, followed this method, their works would have been more pleasing and less confused.

• Glen-Cloy. This glen is nearly three miles long, and haif a mile broad; open towards the east, but bounded on the other sides by high hills. At the top, or west part of the glen, the hills are highest, forming a very romantic groupe of rocks. The north and south sides, which are of considerable height, become gradually lower as they approach the sca, where they form part of Brodick-bay. The bottom of the glen rises gently from the sea, forming a small angle with the hills that bound it. Inmediately under the peat-moss or heather, we discover bor ider stories, which form horizontal beds, from three to thirty Feet thick, and in other places they are collected together in heaps, being thrown into this form by the force of water. These bo vlder stones are not of very considerable size, and vary but little in that respect at the top or bottom of the glen ; which shews that the greater part of them have noi received their rounded form hy attrition in the water of the glen, but are derived from a decomposed breccia. They consist of granite, porphyry, scenite, breccia, and sandstone, which are all to be observed in the neighbouring hills. Through the glen runs Glen-Cloy bura, formed by the springs and rains from the hills ; it is narrow, but, during violent storms, it overflows a considerable part of the glon, and has thus laid bare the rocks, and shew's us in a satisfactory manner the nature of the subjacent strata. The bottom of the glen is composed of the common red co. loured argillaceous sandstone', and licre and there are strata of breccia, and both are traversed with veins of basalt, which run in very various directions, and are fro:n three to twelve feet in breadth. These veins, in their passage through the strata, (to use the Huttonian language,) do not appear to have occasioned in them

any alteration with

regard to hardness ; on the contrary, we often find a species of semi-indurated clay iuterposed between the sandstone and basalt. The hills on the north and south sides of the glen are of the same height, and the pente of the hills appears to correspond pretty nearly with the eleva. tion of the strata. The hills on the south side are formed of sand. stone and breccia, which, towards the

upper end, form precipices. Many veins of basalt traverse the sandstone ; and loose Rodules of a singular species of black pitchstone lie scattered here and there. On the north side, near to Brodick Wood, a very consider. able vein of green coloured pitchstone, much resembling that at the Lamlash road, makes its appearance running through the sandstone. In ascending the hills upon this side, after gaining a considerable height, the sandstone disappears; when a wacken-porphyry is to be observed, and, upon the brow of the hill, where the rains, &c. have made a section of the strata, we observe several curious phenomena. In the first place, we remark the great tendency which the porphyry


very lofty has to assume the columnar form. The next appearance which claims our notice, is the remarkable position of the basaltic veins, which run in various directions through the sandstone and porphyry.'

• The west or upper end of the glen is formed of sandstone, pretty much traversed with veins of basalt, which are more or less inclined, and of various diameters. Besides this sandstone, we observe lofty precipices of scenite, which forin strata elevated at an angle of about 30°. This rock is not only very much varied in the nature of its constituent parts, but also in the degree of the intimacy of combination, which renders it very difficult to determine its different species. It is also penetrated with veins of basalt, but not so much so as the sandstone*. It forms the higher part of several of the hills betwixt the top of this glen and the Shiskin, and is all along penetrated with basaltic veins.

appears, from the description which has been now given, that the sandstone forms by far the greatest part of this glen: the next in proportion is the porphyry, and lastly the scenite.

• No subject is more interesting or useful than an examination of the relative position of strata and veins : in short, upon this is founded all our knowledge of geology. It is, however, attended with great labour and difficulty, not only on account of the many turnings and superposition of strata, &c. but also from the frequent impossibility of tracing these strata in such a manner as to convince us of their relative position. This last circumstance prevented me from determining, with sufficient accuracy, whether the porphyry lay on the sandstone, or the sandstone on the porphyry. One fact inclined me lo suspect that they were both formed at the same time, and that the porplıyry lies upon the sandstone. It was the remarkable vein of basalt rising from the bottom of the glen, through the porphyry, which led me to presume that the sandstone and prophyry were formed at the same time: the vein appearing to rise through the sandstone, and to penetrate the porphyry in the same direction. We have more certainty with regard to the scenite, which appears to be of an origia

•* Dr. Hutton, in his speculations upon the Theory of the Earth, remarks: “ If it be by means of heat and fusion that strata have been consolidated, then, in proportion to the degree of consoli. dation they have undergone from their original state, they should cæteris paribus, abound with more separations in the mass. But the conclusion is found consistent with appearances. A stratum of sandstone does not abound so much with cutters and veins as a similar stratum of marble, or even a similar stratum of sand. stone that is more consolidated; they are in general intersected with veins and cutters; and in proportion as strata are deep in their perpendicular section, the veins are wide, and placed at greater disa tances.” This does not appear to be consistent with fact : for it is to be observed in Arran that the sandstone contains more veins than the scenite, which last is greatly harder than any sandstone in the island; and we observe that the scenite contains a greater number of veins than the granite, although it be softer and less compact.'


« ForrigeFortsæt »