ADDRESS. 5 



tract has a mechanical aspect and is fossiliferous, graduates in another 

 parallel of latitude into a metamorphic crystalline condition, whereby not 

 only the organic remains, but even the original impress of sedimentary 

 origin are to a great degree obliterated.' The same kind of phenomena 

 are common in Canada and the United States ; and Medlicott and Blan- 

 ford, in ' The Geology of India,' have described the thorough metamor- 

 phism of Lower Silurian strata into gneiss and syenitic and hornblende 

 schists. 



In Britain, none of the Upper Silurian rocks have undergone any 

 serious change beyond that of ordinary consolidation, but in the Eastern 

 Alps at Gratz, Sir Roderick Murchison has described both Upper 

 Silurian and Devonian strata interstratified with separate courses of 

 metamorphic chloritic schist. 



Enough has now been said to prove the frequent occurrence of 

 metamorphic action among Cambrian and Lower and Upper Silurian 

 strata. 



If we now turn to the Devonian and Old Red Sandstone strata of 

 England and Scotland, we find that metamorphic action has also been at 

 work, but in a much smaller degree. In Cornwall and Devon, five great 

 bosses of granite stand out amid the stratified Silurian, Devonian, and 

 •Carboniferous formations. Adjoining or near these bosses the late Sir 

 Henry De la Beche remarks, that ' in numerous localities we find the 

 coarser slates converted into rocks resembling mica-slate and gneiss, a 

 fact particularly well exhibited in the neighbourhood of Meavy, on the 

 south-east of Tavistock,' and ' near Camelford we observed a fine arena- 

 ceous and micaceous grauwacke turned into a rock resembling mica-slate 

 near the granite.' Other cases are given by the same author, of slaty 

 strata turned into mica-schist and gneiss in rocks now generally con- 

 sidered to be of Devonian age. 



The Devonian rocks and Old Red Sandstone are of the same geological 

 age, though they were deposited under different conditions, the first being 

 of marine, and the latter of fresh- water, origin. The Old Red Sandstone 

 of "Wales, England, and Scotland has not, as far as I know, suffered any 

 metamorphism, excepting in one case in the north-east of Ayrshire, near 

 the sources of the Avon Water, where a large boss of granite rises 

 through the sandstone, which all round has been rendered crystalline 

 ■with well-developed crystals of felspar. 



On the continent of Europe, a broad area of Devonian strata lies on 

 both banks of the Rhine and the Moselle. Forty years ago, Sedgwick 

 and Murchison described the crystalline quartzites, chlorite, and micaceous 

 slates of the Hundsruck and the Taunus, 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 metamorphic character. In the Alps 

 also, as already noticed, metamorphic Devonian strata occur interstratified 

 with beds of metamorphic schists, and. Sir Rodei'ick adds, ' we have 

 ample data to afi&rm, that large portions of the Eastern Alps . , . are 



