Atigitsi 26, 1S80] 



NATURE 



585 



and from personal observation I know that the rocks in the 

 country on either side of the Moselle are, in places, of a foliated 

 or semi-foliated metaraorphic character. In the Alps also, as 

 already noticed, metamorphic Devonian strata occur interstrati- 

 tied with beds of metamorphic schists, and, Sir Roderick adds, 

 "we have ample data to affirm that large portions of the Eastern 

 Alps . . . are occupied by rocks of bue paleozoic age, which 

 in many parts have passed into a crystalline state." 



I know of no case in Britain where the Carboniferous strata 

 have been thoroughly metamorphosed, excepting that in South 

 Wales beds of coal, in the West of Caermarthenshire and in 

 South Pembrokeshire, gradually pass from so-called bituminous 

 coal into anthracite. The same is the case in the United States, 

 in both instances the Carboniferous strata being exceedingly dis- 

 turbed and contorted. In the Alps, however, Sir Roderick 

 Murchison seems to have believed that Carboniferous rocks may 

 have been metamorphosed : a circumstance since undoubtedly 

 proved by the occurrence of a coal-measure calamite, well pre- 

 served, but otherwise partaking of the thoroughly crystalline 

 character of the gneiss in which it is imbedded, and which was 

 shown to me by the late Prof. Gastaldi, at Turin. 



I am w ell acquainted with all the Permian strata of the British 

 Islands and of various parts of Continental Europe, and no- 

 where, that I have seen, have they suffered from metamorphic 

 action, and strata of this age are, I believe, ar, yet unknown in the 

 Alps. This closes the list of metamorphism of Palxuzoic strata. 



I will not attempt (they are so numerous) to mention all the 

 regions of the world in w hich Mesozoic or Secondary formations 

 have undergone metamorphic action. In Britain and the non- 

 mountainous parts of France they are generally quite unaltered, 

 but in the Alps it is different. There, as every one knows who 

 is familiar with that region, the crystalline rocks in the middle of 

 the chain have the same general strike as the various flanking 

 stratified formations. As expressed by Murchison, "as we fol- 

 low the chain from north-east to south-west we pass from the 

 clearest types of sedimentary rocks, and, at length, in the Savoy 

 Alps, are immersed in the highly-altered mountains of Secondaiy 

 limestone," while " the metamorphism of the rocks is greatest 

 as w-e approach the centre of the chain," and indeed any one 

 familiar with the Alps of Switzerland and Savoy knows that a 

 process of metamorphism has been undergone liy all Ihe Jurassic 

 rocks (Lias and Oolites) of the great mountain chain. Whether 

 or not any strata of Neocomian and Cretaceous age have been 

 well metamorphosed in this region I am unable to say ; but it 

 seems to be certain that the Eocene or Lower Tertiary Alpine 

 formation, known as the Flysch, contains beds of black schists 

 which pass into Lydian stone, and also that in the Grisons it has 

 been converted into gneiss and mica-schist, a fact mentioned by 

 Studer and Murchison. I also have seen in the country north of 

 the Oldenhorn nummulitic rocks so far foliated that they formed 

 an imperfect gneiss. 



In Tierra del Fuego, as described by Darwin, clay slates of 

 early cretaceous date pass into gneiss and mica-slate with 

 garnets, and in Chonos Islands, and all along the greit Cordil- 

 lera of the Andes of Chili, rocks of Cretaceous or Cretaceo- 

 oolitic age have been metamorphosed into foliated mica-slate 

 and gneiss, accompanied by the presence of granite, syenite, and 

 greenstone. 



This ends my list, for I have never seen or heard of metamor- 

 phic rocks of later date than those that belong to the Eocene 

 series. Enough however has been said to prove that from the 

 Laurentian epoch onward the phenomenon of extreme meta- 

 morphism of strata has been of frequent recurrence all through 

 Paleozoic and Mesozoic times, and extends even to a part of the 

 Eocene series equivalent to the soft unaltered strata of the 

 formations of the London and Paris basins, which, excepting for 

 their fossil contents, and sometimes highly-inclined positions, 

 look as if they had only been recently deposited. 



Volcances. — The oldest volcanic products of which I have 

 personal knowledge are of Lower Silurian age. These in Wales 

 consist of two distinct series, the oldest of which, chiefly formed 

 of felspathic lavas and volcanic ashes, lie in and near the base 

 of the Llandeilo beds, and the second, after a long interval of 

 repose, were ejected and intermingled with the strata forming 

 the middle part of the Bala beds. The Lower Silurian rocks of 

 Montgomeryshire, Shropshire, Radnorshire, Pembrokeshire, 

 Cumberland, and Westmoreland are to a great extent also the 

 result of volcanic eraptions, and the same kind of volcanic rocks 

 occur in the Lower Silurian strata of Ireland. I know of no 

 true volcanic rocks in the Upper Silurian series. 



In the Old Red Sandstone of Scotland lavas and volcanic 

 ashes are of frequent occurrence, interstratified with the ordi- 

 nary lacustrine sedimentary strata. Volcanic rocks are also 

 intercalated among the Devonian strata of Devonshire. I know 

 of none in America or on the continent of Europe. 



In Scotland volcanic products are common throughout nearly 

 the whole of the Carboniferous sub-formations, and they are 

 found also associated with Permian strata. 



I now come to the Mesozoic or Secondary epochs. Of 

 Jurassic age (Lias and Oolites), it is stated by Lyell with some 

 doubt, that true volcanic products occur in the Morea and .also 

 in the Apennines, and it seems probable, as stated by Medlicott 

 and Blauford, that the Rajmahal traps may also be of Jurassic 

 age. 



In the Cordillera of South America, Darwin has described a 

 great series of volcanic rocks intercalated among the Cretaceo- 

 oolitic strata that forms so much of the chain ; and the same 

 author, in his "Geological Observations in South America," 

 states that the Cordillera has been, probably w ith some quiescent 

 periods, a source of volcanic matter from an epoch anterior to 

 our Cretaceo-oolitic formation to the present day. In the 

 Deccan volcanic traps rest on Cretaceous beds, and are overlaid 

 by Nummulitic strata, and, according to Medhcott and Blanford, 

 these were poured out in the interval between Middle Cretaceous 

 and Lower Eocene times. 



In Europe the only instance I know of a volcano of Eocene 

 age is that of Monte Bolca near Verona, where the volcanic 

 products are associated with the fissile limestone of that area. 



The well-preserved relics of Miocene volcanoes are prevalent 

 over many parts of Europe, such as Auvergne and The Velay, 

 where the volcanic action began in Lower Miocene times, and 

 was continued into the Pliocene epoch. The volcanoes of the 

 Eifel are also of the same general age, together with the ancient 

 Miocene volcanoes of Hungary. 



The volcanic rocks of the Azores, Canaries, and Madeira are 

 of Miocene age, while in Tuscany there are extinct volcanoes 

 that began in late Miocene, and lasted into times contempora- 

 neous with the English CoralUne Crag. In the north of Spain, 

 als;o, at Olot in Catalonia, there are perfect craters and cones 

 remaining of volcanoes that began to act in newer Pliocene 

 times and continued in action to a later geological date. To these 

 I must add the great coiiUcs of Miocene lava, so w-ell known in 

 the Inner Hebrides, on the mainland near Oban, &c., in Antrim 

 in the north of Ireland, in the Faroe Islands, Greenland, and 

 Franz-Joseph Land. It is needless, and would be tiresome, 

 further to multiply instances, for enough has been said to show 

 that in nearly all geological ages volcanoes have played an im- 

 portant piart, now in one region, now in another, from very 

 early Pala;ozoic times down to the present day ; and, as far as 

 my knowledge extends, at no period of geological history is 

 there any sign of their having played a more important part than 

 they do in the epoch in which we live. 



Mountain Chains, — The mountain-chains of the world are of 

 different geological ages, some of them of great antiquity, and 

 some of them comparatively modern. 



It is well known that in North America the Lower Silurian 

 rocks lie unconformably on the Laurentian strata, and also that 

 the latter had undergone a thorough metamorphism and been 

 thrown into great anticlinal and synclinal folds, accompanied by 

 intense minor convolutions, before the deposition of the oldest 

 Silurian formation, that of the Potsdam Sandstone. Di>turb- 

 ances of the nature alluded to imply beyond a doubt that the 

 Laurentian rocks formed a high mountain-chain of pre-Silurian 

 date, which has since constantly been worn away and degraded 

 by sub-aerial denudation. 



In Shropshire, and in parts of North Wales, and in Cumber- 

 land and Westmoreland, the Lower Silurian rocks by upheaval 

 formed hilly land before the beginning of the Upper Silurian 

 epoch ; and it is probable that the Lower Silurian gneiss of 

 Scotland formed mountains at the same time, probably very 

 much higher than now. However that may be, it is certain that 

 these mountains formed high land before and dming the depo- 

 sition of the Old Red Sandstone, and the upheaval of the great 

 Scandinavian chain (of which the Highlands may be said to form 

 an outlying portion) also preceded the deposition of the Old Red 

 Strata. In both of these mountain regions the rocks have since 

 undergone considerable movements, which in the main seem to 

 have been movements of elevation, accompanied undoubtedly by 

 that constant atmospheric degradation to which all high land is 

 especially subject. 



