As an instance of the unscientific play of the imagination we may note the imaginary basis of a theory proposed by even the great Sedgwick, when he conceived that "both cleavage and foliation are due to the parallel transmission of planes or waves of heat, awakening the molecular forces and determining their direction "-a view endorsed (as it appears) by Prof. H. D. Rogers. The unreality of the basis on which it rests is seen at once by bringing it to the test of a few simple physical principles, based on unquestionable experimental data.

We know of three ways in which heat is transmitted:

The first is clearly out of the question; the second is equally inapplicable to a solid mass; the third is nothing more than a tendency towards equilibrium in the heat-energy contained in a system, by virtue of which when masses of matter are in contact at different temperatures, there is a constant transfer of heat from the hotter to the colder masses until equalization of temperature throughout the system is attained. But the propagation of a series of waves of heat,' would require also the converse of this; which is about as possible as that water should flow up-hill under the mere influence of gravitation. The apparent analogy of the propagation of sound-waves in such an elastic medium as air (coupled with the obsolete caloric-hypothesis) where the alternate condensation and expansion of a material body form the counterparts of each other in every undulation, probably misled Sedgwick.

NOTE F.

The terms' vitreous' and 'amorphous.'

It will be seen that in this work the term 'amorphous' is used in a more limited sense than is common among mineralogists, with whom it is customary to include those forms of matter which are here distinguished as 'glassy' or 'vitreous.' (See Rammelsberg, Handbach der Mineralchemie, pp. 38-40). That authority defines (p. 38, loc. cit.) amorphism as follows: Die Masse eines festen Körpers wird amorph genannt, im Gegensatz zu krystallisirt, wenn die Kennzeichen des krystallisirten Zustandes ihr fehlen." The facts considered in the thesis in connexion with devitrification have rendered it necessary to adopt the nomenclature of chemistry rather than of mineralogy; since its aim is rather to get at the principles-the natural operations-which determine those phenomena, the description of which is the proper function of the pure mineralogist At the same time the difficulty of drawing a sharp line of distinction between non-crystalline bodies is not unperceived, since these graduate from the condition of a true glass through the various phases expressed by the terms 'opalescent,' 'gelatinous,' 'flocculent,' to that which is implied by the term 'amorphous,' as it is used in chemistry. The following examples of variations in spec. gravity with allotropic forms given by Rammelsberg (loc. cit p. 39) may be compared with the cases cited in this work:

(1) The lighter form of 'crystalline' sulphur given as having a specific gravity of 196 is the sulphur-glass of the prismatic crystallites, which have

generally (I believe always) been hitherto described by chemists as 'crystals;' upon the strength of which sulphur has been spoken of (as it would appear erroneously) as a 'dimorphous body,'

(2) The same confusion appears in the case of phosphorus, and introduces what appears at first sight an anomaly, which, were it anything more than an apparent exception, would vitiate the generalization enunciated in this work; but on the other hand causes no difficulty, when it is seen that it is in reality the vitreous form of phosphorus which has the density of 1.82. (3) The 'amorphous' orthoclase is really the glass.

The facts are quite sufficient to justify the distinction which has been drawn in the text of this work between vitreous and amorphous bodies in the chemical sense.

From recent observations I have been led to recognise vitreosity as a phenomenon occasionally exhibited by water under conditions favourable to rapid loss of heat at O°C. (See Nature, vol. xxxvii, p. 104).

The facts cited certainly lend support to the view advocated in this work as to latent heat of vitrification; and the fact of the greater brittleness in frosty weather of ordinary window-glass-which is a matter of common observation-may perhaps be explained on the same principle. Further investigation may possibly also lead to our recognition of vitrification as the real explanation of the silvery blue tint which characterizes 'glacier-ice.'

NOTE G.
On Fritting.

Since the suggestion as to the possible formation of Wollastonite by direct replacement of CO2 by SiO2 in the dry way was written, I have had the privilege of seeing in Dr. Percy's collection a fine specimen of Wollastonite, made some years ago in his laboratory, by heating finely powdered calcite and fine clean quartz sand together in equivalent proportions. On turning to p. 46 of the new edition of the volume on Fuel, &c., by that distinguished metallurgist, we find the rule laid down, that 'Silica combines readily with a metallic oxide, when an intimate mixture of the two is heated to the right degree, provided the oxide be not reducible, per se, at or below the temperature required for combination.' And he points out that fusion is not necessarily required for combination (e.g. in the case of silica and lime), and in metallurgical operations in the process known as 'fritting,' is to be avoided with an easily fusible oxide of a heavy metal (e.g. protoxide of lead).

The occurrence of Wollastonite as a product of contact-metamorphism has been recorded by Prof. Heddle in the marbles of the north-western portion of the Scottish Highlands. (See Q.J.G.S., vol. xliv, p. 411).

The fact that 'slags' are composed of silicate of lime and other silicates formed in the dry heat of the furnace, is most important in its petrological bearing; and must always be borne in mind as a caution on instituting any comparison between them and the silicates found in the crystalline rocks, -the schists on the one hand, and the eruptive rocks on the other. This consideration too tends to confirm the theory advocated in this work, that the original minerals of the schists have crystallized in the presence of superheated water, though not 'precipitated' in aqueous basins.

NOTE H.

Orographic Structure of the Alps.

The importance of looking at the structure of a comparatively young mountain-system is seen from the fact that most of the mountains of these islands are but the worn-down stumps of ancient mountain-systems. Nonrecognition of this fact has it appears, led to some erroneous theorizing among the untravelled members of the British fraternity of geologists: they have mistaken the abnormal for the normal relation of things, and have been in consequence a little too ready to arrive at advanced theories as to

'regional metamorphism.' The recent publication of Prof. Heim's great work Mechanismus der Hochgebirgsbildung has opened their eyes to some leading principles which have been for some years more or less patent to the leading geologists on the continent (Switzerland, Austria, Germany). I shall sketch here briefly a few of my own observations made during several traverses of the main or central chain of the Alps in past years (chiefly from 1877 to 1883); premising that the general orography of the Alpine system -a central chain of crystalline rocks with flanking chains of sedimentary rocks, (mainly of Secondary and Tertiary ages)—is known to everyone who takes an interest in this subject.

My first traverse was made from Flüelen by Altdorf, Amsteg, and the Kreuzli Pass to Sedrun and Dissentis in the Vorderrheinthal. This pass is somewhat rough and unfrequented, but has the advantage (to the geological observer) of being free from glaciers. One could not fail to be struck, as one penetrated the mountains from the north, with the distinct succession of slates, schists and gneiss into the alpine granite which seemed to form the backbone of the range; the same succession (in part) being seen in reverse order as one descended to the V. Rheinthal, and in a walk down the Reussthal another time from Andermatt to Amsteg. The valley of the Vorder Rhein is apparently formed by a gigantic flexure in the main chain, which has left the oldest rocks covered up by a series of younger schists of undetermined age, including the Bündner* and Casanna Schiefer (the "schistes gris" and "schistes vertes" of the Swiss geologists), and some later formations, including the Verrucano. Leaving the main valley at Ilanz, and striking up the side valley to the south, one passes through these younger phyllites and schists, all the way up the valley to Vals-am-Platz. Near Furth I found talc-schist, and higher up the valley the green schists (schisteverte) and marble (calcaire indéterminé) interbedded with the grey schists (schists gris). I have twice traversed this valley, and have thus repeated the observations. The second time one had rather exceptional advantages from the fact that a new road was in process of construction, and the blasting-works had laid bare large exposures of fresh rock-surface. The foliated structure of these rocks at a very high angle has facilitated the erosion by the mountain stream of most magnificent gorges, quite comparable with that of the Via Mala for depth and narrowness. On my first traverse the Pass of the Valserberg was covered with snow; but on the second occasion it was free from it; and I observed what appeared to be the green schists forced in contorted masses into the older schists. On referring to Studer and Escher's map I find the green schists and marble shown as cutting through this range into the Hinterrheinthal, between the older mica-schists and the grey-schists. These last are met with down the Valley as far as Splügen. In the road cuttings between that place and Andeer the mica-schists and gneiss are well exposed, and have a decidedly older look than the schists of the Valserrhein. Two different routes were taken on the two several traverses from the last-named place to Bivio-Stalla, at the foot of the Julier Pass.

On the first occasion the wild steep rough valley of the Averser Rhein was followed up to Cresta (the loftiest Swiss village according to Bädeker). The lower part of this valley has a wildness and ruggedness almost peculiar to it in my experience; and on referring to the map, this seems to be accounted for by the fact that it is cut through the oldest schists and gneiss which

Local geographical name (Von Hauer) from the territory of the mediaval 'Bund.'

+ Field observations on these green schists of this region of the Alps certainly suggested even at that time (1878) an igneous and intrusive origin for them. (cf. Kalkowsky, op. cit., p. 217). They are probably the Valrheinit' of Rolle.

are much more indurated than those of the younger series of schists developed higher up the valley. Mining for metallic ores is carried on in the older series. Crossing over the Stallaberg, dykes of green serpentine with a pseudo-fibrous cleavage are seen cutting through the mountain and well exposed by the side of the mountain-path which crosses them.

On the second occasion the route was from Andeer by the Via Mala to Thusis; thence by the Schyn Pass, Tiefenkasten, and the Oberhalbsteinthal to Bivio. The deep-cut steep gorges of the Schyn reminded one of those of the Valser Rhein, and this character the two valleys seem to possess in common from the fact that they are both cut into the younger schists, as in fact is the gorge of the Via Mala, where the rocks are of a more calcareous character; an instance of these grey schists becoming in places massively kalkhaltig, (Gümbel). Green and red serpentine is so abundant in the Oberhalbsteinthal as to be used commonly for road material; and about Mühlen this mineral appears to permeate the 'green schists.' I obtained opposite the hotel at this place a specimen of a highly-contorted portion of these schists, with marked foliation. Ascending the Julier we have (1) Casanna Schist, (2) Gneiss, (3) Granite (intrusive); and portions of the schists are found above the Pass; while lower down, on the south side, a quartzite (probably grauwacke) is quarried by the road-side. These appear from their position to be portions of once-larger masses infolded in the granite and gneiss in the process of mountain-building. I have studied the gneiss and schist of the Upper Engadine from the Maloja Pass to Samaden, and have been impressed with the strong evidence in them of some sort of bedding. The serpentine too of the Oberhalbstein was observed cutting through into the valley above Silvaplana. The granite of the Roseggthal, the gneiss about Samaden and St. Moritz, the granite and gneiss of the Bernina Strasse and the schists of the Alp Grün have all been studied 'in the field.'

On one occasion I returned from the Engadine by the Suvrettathal and the Val Bevers, then over the Weissenstein granite massif, dropping down to the Albula Strasse near the top of the pass. Walking down to Bergün, good road-sections were seen in the Liassic slates, the cleavage of which was so pronounced, that the eye could follow its strike through the mountains to the north west. On petrological grounds alone, and quite independently of their organic remains, I should say there was no difficulty in distinguishing these slates from the phyllites of the older (archæan) series.

From Bergün Davos-am-Platz was reached by the Sertig Pass and Frauenkirch, the older schists being seen in the lower part of the Sertigthal. From Davos Landquart was reached by the road through the Prättigau, the valley traversing the younger or grey schists and phyllites. On another occasion the same series of schists and phyllites was studied in a journey from Tiefenkasten by Lenz and Churwalden to Chur.

Impressions strongly forced in upon one's mind in these travels and observations were such as the following:

(1) The fact of a general order of succession prevailing in the oldest and most highly 'metamorphosed' strata of the Alps;

(2) The existence of more than one series of schists, those of some districts having altogether a younger and less indurated character than those of other districts where they are directly related to the central or fundamental gneiss ;

(3) Frequent strong signs of some sort of bedding, even down to the gneiss; marked examples of which were observed in the Reussthal and on the Maloja; (4) Signs in some cases of subsequently-induced subordinate structural characters, such as cleavage and the deposition of veins of secondary quartz. Of the rapidity with which the younger phyllite series undergo degradation by atmospheric agents in weathering, as compared with the older schists, I have noted several illustrations, in the work done by great downpours of rain in the mountains. For example, a storm during the previous night

had swollen the waters of the Nolla which rolled like a sea of black mud into the Rhine at Thusis; and about half-an-hour from that place the road to the Schyn Pass was found blocked by a vast mass of debris from the same black slaty rocks of the phyllite series.

Again in wandering in the Bavarian Alps, in the Vorarlberg, and in the Salz Kammergut on the north side of the Alps; in contrasting the calcareous series of the north side of the Ennsthal with the micaschists on the south side; in contrasting the Triassic strata of the Dolomite Alps to the south of the Pusterthal with the phyllites the mica schists and the gneiss of the central chain on the north side of that valley; and lastly in following the latter up the valley from Lienz to Heiligenblut and on to the Gross Glockner, one could hardly help reflecting upon the slight petrological change wrought in the later and undoubted sedimentary series with the enormous degree of 'metamorphism' which the rocks of the central chain had undergone, on the assumption that they owe their present character altogether to 'metamorphism.' This is especially striking when one compares, in hand-specimens or in field-sections, the Triassic limestones on either the north or south side with the massive calcareous schists (Kalk-glimmerschiefer) which are seen interbedded with the chloritic schists and above the mica-schists of the Glockner, * (exposed in good fresh sections below the Glockner House.) The slight splintery kind of incipient cleavage, which has given to the 'Dolomites on the south side and to ranges like the Donner Kogeln on the nor thside above Gosau their weird and grotesque appearance (as the result of the peculiar mode of weathering caused thereby in these rocks), and is well seen in hand-specimens of some of the Hallstatt limestones (which have undergone a certain amount of metatropic change in places into marble),-is altogether a different thing from the marked foliation observable in the Kalkglimmerschiefer of the Glockner district.

Reflecting on such facts, one found oneself gradually driven of necessity to conclude that the mere pressure, which has wrought so small a petrological change in the sedimentary strata of the flanking ranges of the Alps, cannot be accepted as the cause of the petrological characters peculiar to the gneiss and schists of the central chain. Some of the extreme results of such pressure are seen in the true cleavage of the Glarus slates (Dachschiefer) where the Eocene strata have been subjected to excessive pressure between two great overfolds of the older strata (Doppelfalte,) + and of the slates of some of the secondary formations of the Alps (as in the case cited in this note and other well-known instances); and I have a specimen of rock from the Schafberg above Pontresina (probably originally a quartrite) in which a rough cleavage-foliation cuts right across the bedding. No one would contend

* Position assigned to them by Gümbel. (Anleitung zu wiss. Beobach. auf Alpen-reisen, fig 52), cf. Bonney, (Q.J.G.S. vol. xlv, pp. 86-90).

+ See Heim, Mech. der Gebirgsbildung, (Atlas, prof. v, vi, vii, viii.) In the text of that work (Bd. i, pp. 143-146) Heim has given in full the palæontological and lithological evidence of the Eocene age of these Glarus slates.

The "quartzite in which a rough cleavage-foliation" has been developed appears to be a schist, composed of alternate layers of a brownish yellow mica and quartz, the mica occurring in very thin layers, little more than films, under the microscope. The quartz has the 'mosaic-like' texture, and some of it appears to have taken the form of tridymite, as if the rock had been partially fused. On the other hand many of the quartz grains strongly suggest a clastic origin for the original rock. These facts and the proximity of the rock to the granite seem to suggest that the character of the rock is the result of contact-metamorphism. It is also intimately associated in the same quarry with a schistose chloritic rock, which as seen under the micr. must I think be certainly considered a product of contact-metamorphism. There is an accessory mineral scattered pretty

I