Observations on Serpentine and Diallage Rocks. By Dr A. BOUE. In a Letter to Professor JAMESON. Communicated

by the Author.

THE geological relations of serpentine are still but imperfectly known; for it is not many years since we were assured of the existence of transition serpentines in the form of short beds, or large masses in the veins, or bed-like veins, of the greenstone (diabase) of the Pyrenees (St Pé, and Valley of Baretons); in the greywacke of Girvan and Ballantrae in Scotland (Jameson), and of Bastberg in the Hartz; in the transition slates of the northern Fichtelgebirge, and of the Vosges; in the transition limestone of Willendorf in Austria; in the Carpatho-Appenine sandstone of Waidhofen in Lower Austria, of Monte Ferrato, near Prato, Impruneta, Creboli, &c. in Tuscany, and of Borghetta in Liguria. Veins of serpentine have been detected by the geologists of Scotland, in the old red sandstone of Forfarshire.

Some of these masses present characters illustrative of an igneous and violent origin, and throw light on the true situation and formation of other serpentines, whose contact with neighbouring rocks either has been but imperfectly seen, or not seen at all. The serpentine of Willendorf is a fine example of the injection of this rock amongst older strata. It is situated about half a mile to the west of that village, and on the right hand side of the road leading to Granbach. The limestone hills are bordered by reddish precipices, in the midst of which, the geognost sees with astonishment a thick columnar mass of serpentine rising through the limestone, to the height of 100 feet, and fairly terminating in the surrounding limestone rock. This mass is 60 feet broad below, 40 feet broad at top, has an undulating contour, and a blackish knotted surface, as if composed of irregular spherical bodies. Small veins of asbestus and calcareous spar are contained in it, but no distinct diallage rock. It is intimately united with the transition magnesian limestone which it intersects; and between the two rocks there is a breccia composed of a mixture of the limestone and serpentine. Even the limestone itself is impregnated with serpentine matter. All the neighbouring rocks are more or less vesicular, and deeply

coloured with red oxide of iron, so that they present to the eye a very singular and sterile aspect. The marly or argillaceous inclined strata at their base, are partly violet and reddish, and contain small veins of micaceous iron ores. In short, this locality of serpentine may be considered as illustrating the elevation of that rock from below, in the same manner as porphyry and the accompanying breccia intimate the violence of the action.

The position of the serpentine of Tuscany has already been ably described by Brongniart, although not in a complete manner, as that distinguished observer has omitted to notice several accompanying interesting phenomena. For instance, in the Valley of Garignola, the serpentine and diallage rock or euphotide, not only cover a part of the limestones and marls, which are converted into reddish jaspideous rocks; but they rise through them, and extend over them on all sides, so that they have the shape of a wedge-shaped bed, or that of a mushroom. The breccia formed of limestone and diallage rock, which Brongniart places above the jasper, does not occur every where; but only in those places where diallage rock comes in contact with broken and bruised marls and marly limestone. The limestone is then sometimes changed into a granular mass. In Austria, about one hour's walk from Waidhofen, on the northern side of the Ips, there is a hill of serpentine apparently resting upon the same marly sandstones and marls as occur in Tuscany; and not far from it, there are in those slates which contain fossil ferns, beds of bituminous and slate coal, which are regularly worked. The lowest part of this deposite probably belongs to the independent coal formation.

If our acquaintance with these more recent serpentines be increasing, geologists have not yet fixed the age of the serpentines placed amongst slaty crystalline or primitive rocks. In this class, are generally enumerated the following masses :-the serpentines of Shetland (Jameson), and of the North Cape (Buch); the bed-like veins of Portsoy (Jameson), and of the Lizard Point in Cornwall; the great zone of serpentine of the departments of Arveiron, Lot, Correze, and Upper Vienne; the hillocks of serpentine and diallage rock in the talc slate of western Liguria, and of the base of the Piedmontese Alps; of the Alps in the department of the High Alps (Brainçon, Villard, St

Veran); of Mont Rosa and of the Grisons; the serpentinous rocks of the Tyrol; of the chain of the High Tauerngebirge in Salzburg; of the Pinzgau, of Stiria, Austria; of the Rosalingebirge near Bernstein in Hungary; of the Eastern and Western Böhmerwaldgebirge; of the Fichtelgebirge, of Saxony, Silesia; and of the Carpathian Chain and of Wallachia.

The greater number of these serpentines are situated in talcose slates, or among the most recent primitive slates; some few are associated with whitestone or leptinite, as in Saxony, between Waldenheim and Waldenberg; in Austria at Grabenhof, near Gansbach; at Altenburg on the Kamp; and at Namier in Moravia. Some others are in gneiss, or even in granite, as at Töplitz in Saxony; also in the Fichtelgebirge, Böhmerwaldgebirge, the Tyrol, and Stiria. These serpentine deposits are sometimes very considerable, forming occasionally groupes of mountains, as the Mont Rosa in Piedmont, in Liguria, and Hungary. In other quarters, they appear only under the form of bed-like veins or short beds. These last are some feet or fathoms in thickness, as at Lettowitz in Moravia, Portsoy in Scotland, &c.; or they are so thick as to form hills, or the summits of hills, during many miles, as in Liguria, near Genoa, Savona, in the Fichtelgebirge, and in the Shetland islands.

Serpentine hills have a sterile, dark, and knotted surface, not unlike that of hypersthene syenite; and their immediate junction with the primitive slate is seldom visible. On the other hand, the great beds of serpentine usually contain imbedded masses of slate and limestone; and these differ somewhat in structure from the neighbouring rocks of the same kinds. In this way, the bed-like veins of Portsoy contain blackish green talcose rocks, which are slightly slaty, and seem to have been fused in the serpentine mass; and this last rock is closely united with hornblende rocks. In western Liguria, great beds of serpentine inclose quartzose and talcose slates, which are much broken and contorted; or they contain immense masses of limestone, which are to be viewed as fragments or displaced masses, because their stratification is not the same as in the limestone next to the serpentine vein; and besides this, limestone is cracked, granular, foliated, and magnesian.

These elliptical serpentine masses are separated from the talc slates or mica slates, by layers of a singular talcose or brecciated rock. These brecciated rocks remind us of the breccia of basalt and talc-slate, which border some basaltic bed-like veins of talc-slate, near Recoaro, in the Vicentine; but these breccias are never so distinct as those which separate the euphotide and the jaspideous rocks near Borghetto in Liguria, which › are described by M. Brongniart.

The nature of serpentine rocks is not every where the same. There are three sets of these rocks, viz. Serpentine, with dial-› lage and diallage rock; Hornblendic serpentines, with diallage, chromate of iron, and diorite or transition greenstone, (Pyrenees); and, Serpentine originating from augite rocks, through a superabundance of magnesia, as those of Inch Columb, discovered by Jameson. Of these sets of rocks, the first mentioned are the most common, the last the least frequent. In the second class may be placed those small nests of serpentine included in the granular limestones of some mica-slate districts, as that of Glen Tilt. No diallage occurs in them, but the limestone contains hornblende and augite, and the imbedded masses of precious serpentine may have been produced by the vicinity of granitose or syenitic rocks, as at Canzacoli in the Tyrol, where a Jurassic dolomite limestone has been in this way changed into a granular limestone with serpentine veins. The diallage serpentines are not every where associated with euphotide or diallage rock: thus it is not met with in the small veins or small beds of serpentine, and even diallage is rare in those serpentines, as in Moravia, at Portsoy, in Transylvania, &c. In the leptinite, or even in the granitic gneiss, the serpentine is without diallage; but there it frequently contains garnets, as at Zöblitz, Grabenhof, Mezeborz, and Jungeroschiz in Moravia. On the other hand, when serpentine occurs in great hills, it is mixed with euphotide or diallage rock, as in the Hartz, Liguria, Appenines, Carpathians, Silesia, and north of Europe. It is further worthy of remark, that these great masses of serpentine are not every where accompanied with those dark diallage porphyries, with saussurite and diallage and variolites, which are met with in Piedmont, Briançon, Western Liguria, the Hartz, Southern Scotland, and England. These variolites bring to recollec

tion the globular form and stellular structure of the porphyries of Corsica and the Thuringerwald, of the pitchstones of Arran and Meissen, and of the pearlstone of Hungary. These interesting rocks generally border the greater masses of serpentine, as is seen near to Genoa; but they do not appear along the serpentine hillocks of the marly and arenaceous deposite of eastern Liguria and Tuscany.

Euphotide sometimes appears in isolated hills beside the serpentine; in other cases the rocks pass into each other, or they are so interwoven with each other that the one rock forms dikes or distinct veins in the other. The hills between Braco and Matorana, in Liguria, afford a fine example of this appearance. The whole may be explained on the principle of the slow cooling of the mass.

Lastly, The numerous simple minerals met with in serpentine do not occur in it every where. Diallage and asbestus, derived from hornblende and augite, are of these by far the most frequent. Garnets, augites, and hornblendes, are principally met with in the small beds, as those of Portsoy, Heidenberg, Fichtelgebirge. Chromate of iron occurs in the great bodies of serpentine connected with the talcose formation, as in the island of Unst in Shetland, central France, Golsen near Leoben, and Kraubach in Stiria: the same is the case with the native copper of America, &c. and the workable nests of pyrites at Monte Ramazzo, near to Genoa. Magnesite abounds much in some localities, as Hrubschitz in Moravia, Gurhof in Austria, Baldissero, Castellamonte, &c.; when this is the case, the serpentine contains semi-opals and calcedony, as at Gersec in Moravia, and chrysoprase, as at Kozemutz in Silesia, and Besenoro in Syrinia. These siliceous minerals are to the serpentine in the same secondary relation as the small similar veins in the granite, with kaolin and scapolite, at Hafnerzell in Bavaria.

Are we to admit that there are five different formations of serpentine; and, consequently, that it has been erupted at five different periods? In this view we would have, first, a serpentine, posterior to the marls and sandstones of the Appenines and Carpathians; a second, posterior to the transition red sandstone; a third, posterior to the greywacke; a fourth, to the mica slatę; and, a fifth, to the gneiss and leptinite. But has ser