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sionally nodules of chalcedony and conchoidal hornstone, were observed. In the fissures of the rocks, the beautiful Cyathed fragilis was abundant. The temperature of a spring, evidently perennial, on the south-eastern base of the hill, was 47° Fahr.

In the forenoon of the 22d, we reached the far-famed Staffa, and were peculiarly fortunate in having it in our power to enter Fingal's Cave, in a boat, without being much incommoded by the swell of the sea. The shores of this island exhibit well marked sections of the beds of amygdaloid and basalt, of which it consists, and offer no obstacle to an examination of the forms, structure, and bendings of its interesting columns. On the soil, the Orobanche rubra was observed in plenty, but in fruit; and an abundant supply of the eatable mushroom was procured.

In the afternoon of the same day, we visited the ruins of Iona, Ì had time to glance only at the strata of clay-slate near the landing-place, at the ruins, and to break off a specimen from the red granite blocks which were in the neighbourhood. This last, however, was not without interest, as it contained, besides a few scattered crystals of hornblende, numerous depressed doubly oblique prisms of Sphene.

The weather was unfavourable during the whole of the 23d. On the 24th, we touched at Isla, landing at Portnahaven; and, on the morning of the 25th, we found ourselves a-breast of the Giant's Causeway. The basaltic scenery here, though superior to that of Staffa in height and breadth, and the patches of rich green pasture with which the dark ground is relieved, is yet destitute of that distinctness which adds so much to the elegance of Fingal's Cave. At the Causeway, the accumulations of debris conceal much that would interest. At Staffa, every thing is exposed, the sea washing away the disintegrated portions as speedily as they are produced. The rocks, however, are the same at both places, being basalt and amygdaloid; but here the latter is more varied in its contents, and the whole mass of trap rests on chalk. Upon landing at the Causeway we were soon joined by a host of natives, exhibiting, in their tattered dress,' flattering appellations, and impetuous manner, their peculiar marks. Each vied with his neighbour in praising his own qualifications as a guide. Specimens collected from the neighbouring cliffs, and contained in small boxes of rude workmanship,

were eagerly offered for sale. Among these, we picked out the following minerals. 1. Calcareous Spar, of a brownish colour. 2. Cubizite, transparent, and regularly crystallized; and, when occurring in the same cavity with the preceding, usually occupying the place nearest the walls. 3. A mineral resembling Thomsonite, but not yet sufficiently examined. Only two small specimens of this mineral were observed, though eagerly sought after. Hence it is probably of rare occurrence. These had formed a coating on the interior of a cavity in the amygdaloid, and exhibited perfect crystals shooting from the base. 4. Arragonite. This occurs massive, of a white, grey, or palegreen colour, and scopiformly narrow radiated structure. Even where much mixed with the rock, it still appears capable of exercising, that influence which produces its radiated appearance.

Leaving the Causeway, we bent our course towards Portrush, where we again joined the vessel, visiting, in our progress, the extensive quarries of chalk, and glancing at the amygdaloid, with its incumbent augite-greenstone in the neighbourhood of the harbour.

The strata in the immediate stretching in a south-westerly The slate is thick slaty, and

On the 26th, we landed at the light-house situate at the west side of the Mull of Cantyre. neighbourhood, are of mica-slate, direction, and dipping eastward. consists of a basis of grey quartz and silvery mica, with oblong, opake and translucent concretions of quartz. The same kind of mica-slate likewise prevails to the north of the town of Campbeltown, and occupying a similar position. At the latter place, however, it in general contains more mica, and is thin slaty, and characteristically waved. Eastward from a quarry, near the town, of this mica-slate, and in conformable position, and even interstratified therewith, are numerous beds of sandstone and trap conglomerate, foliated limestone, red slate-clay, and red sandstone. Near the extremity of the north side of the bay, these beds are covered with greenstone and amygdaloid, and a coarse clayey basalt. The latter rock is, in some places, columnar; but the columns, which are vertical, are frequently separated several inches from one another, the interval being filled up with ferruginous clay-green earth, calcareous-spar, or a substance resembling sandstone. Compact and hematitic red iron

stone abounds in these spaces, and in numerous veins with which the rock is traversed. On the south side of Campbeltown Bay, the same series of slaty rocks occurs, with the addition of a thick bed of reddish compact felspar-porphyry. The most interesting beds in the whole of this series are the Limestones. These are of two kinds; both, however, granularly foliated, (and, as far as was observed) destitute of organic remains. The first is common, small granular limestone, of a reddish colour, in the form of thin beds in the sandstone. The second constitutes the mineral termed Foliated or Sparry Lucullite. It is of a velvet black colour, and appears in the form of angulo-granular portions, from a quarter to half an inch in size. These may be regarded as imperfect rhomboidal crystals. They are closely united by white, fine granular limestone. The stone is extensively quarried and burnt for lime, on the north side of the bay. The strata are somewhat irregular. The surfaces of each present protuberances indicative of the concretions; or, in consequence of the cementing matter being raised, a singularly reticulated aspect is exhibited. The fracture of the concretion is usually slightly curved foliated; but, in some cases, the fracture is straight foliated, and the angles of the rhomb have the same value as calcareous spar. The black colour of the concretions arises from the intimate mixture of charcoal. This is easily manifested in their solution in acids, by the black powder which remains. By what power, it may be asked, has the charcoal been separated from the cement, and incorporated exclusively in the concretions? The charcoal seems mechanically mixed; and hence probably gives the curvature to the planes of the spar, in the concretions. The dark colour and foliated fracture of the concretions, contrasted with the white colour and fine granular fracture of the connecting matter, render this rock, in hand specimens, one of the most beautiful minerals of which Scotland can boast.

On the morning of the 30th, I took leave of my kind, and attentive friend, and embarked on board the Britannia steampacket for Glasgow.

ART. XIV.-Observations on Double Stars. By M. STRUVE of Dorpat. (Continued from Vol. IX. p. 341.)

THE very interesting observations of M. Struve of Dorpat,

which we laid before our readers in the last Number of this Journal, we are now able to continue, from the Correspondance Astronomique of Baron Zach, who has extracted them from the second volume of M. Struve's Collection of Astronomical Observations. The same class of observations is continued in the 3d volume of the same Recueil, so that we shall have occasion to resume the subject in a future Number.

17. a Cassiopeia. R. Asc. Oh 30. Decl. 55° 33′ N.

2d-3d and 9th-10th Magnitudes.

The

As the small star changes both its distance and its angle of position, it must describe an ellipse round the great one. following are the observations:

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18. Cassiopeia 78. R. Asc. 0h 38'. Decl. 50° 27′ N.

Stars of variable Magnitudes.

According to Sir W. Herschel, these stars were in 1780 of very unequal magnitude, and difficult to be seen. M. Struve sees them at present with difficulty, and their magnitude is nearly equal, viz. 7.8. The distance is supposed to increase.

1780.7, Angle of Position 50° 30' S. Foll. Herschel.

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19. 65 Pisces. R. Asc. 0h 40. Decl. 26° 43′ N.

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Sir W. Herschel found the angle of position 30° 57′ N. Prec.

20. Pole Star. R. Asc. Oh 56'. Decl. 88° 21' N. 2d and 11th Mag.

M. Struve has found for the effect of parallax-0".32, but in the opposite direction to which it ought to be. The constant of aberration was 20".112, whereas he found it 20".300 by other stars. Baron Zach found it, from Bradley's observations, to be 20".232; Bradley made it 20."25, Delambre 20."255, and later astronomers 20".36. The following are M. Struve's observa

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21. y Aries. R. Asc. 1h 44'. Decl. 18° 55' N.

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M. Struve considers that the differences are attributable to errors of observation, and not to any motion in the stars.

22. a Pisces. R. Asc. 1 53', Decl. 1° 53′ N. 3d-4th and 5th-6th Mag.

Angle of Position in 1781.8, was 67° 23′ Herschel,

1802.1, 63 0 Ditto.

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M. Struve thinks that none of the stars move.

23. y Andromeda. R. Asc. 1h 53'. Decl. 41° 28′ N. 3d and 5th Mag.

The largest of these two fine stars is yellow, and the smallest blue.

Angle of Position in 1781.8, was 19° 37' Herschel.

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