4 REPORT 1880. 



tionisiug the geology of nearly one-half of Scotland. To the same age 

 belongs by far the greater part of the broad hilly region of the south of 

 Scotland that lies between St. Abb's Head on the east and the coast of 

 Ayrshire and Wigtonshire on the west. In the south-west part of this 

 district, several great masses of granite rise amid the Lower Silurian 

 rocks, which in their neighbourhood pass into mica-schist and even into 

 fine-grained gneiss. 



In Cornwall tbe occurrence of Silurian rocks is now well known. 

 They are of metamorphic character, and partly associated with granite ;, 

 and at Start Point, in South Devonshire, the Silurian strata have been 

 metamorphosed into quartzites. 



In parts of the Cambrian areas, Silurian rocks in contact with granite 

 have been changed into crystalline hornblendic gneiss, and in Anglesey 

 there are large tracts of presumed Cambrian strata, great part of which 

 have been metamorphosed into chlorite and mica-schist and gneiss, and 

 the same is partly the case with the Lower Silurian rocks of the centre 

 of the island, where it is almost impossible to disentangle them from the 

 associated granite. 



In Ireland similar metamorphic rocks are common, and, on the 

 authority of Prof. Hull, who knows them well, the following statements 

 are founded :— ' Metamorphism in Ireland has been geographical and not 

 stratigraphical, and seems to have ceased before the Upper Silurian 

 period. 



' The epoch of greatest metamorphism appears to have been that which 

 intervened between the close of the Lower Silurian period and the 

 commencement of the Upper Silurian, taking the formations in ascending 

 order. 



' It is as yet undecided whether Lauren tian rocks occur in Ireland. 

 There are rocks in north-west Mayo very like those in Sutherlandshire, 

 but if they are of Laurentian age they come directly iinder the meta- 

 morphosed Lower Silurian rocks, and it may be very difficult to separate 

 them. 



' Cambrian purple and green grits are not metamorphosed in the coun- 

 ties of Wicklow and Dublin, but the same beds at the southern extremity 

 of County "Wexford, near Carnsore Point, have been metamorphosed into 

 mica-schist and gneiss. 



' In the east of Ireland the Lower Silurian grits and slates have not 

 been metamorphosed, except where in proximity to granite, into which 

 they insensibly pass in the counties of "Wicklow, Dublin, "Westmeath, 

 Cavan, Longford, and Down ; but in the west and north-west of Ireland 

 they have been metamorphosed into several varieties of schists, horn- 

 blende-rock, and gniess, or foliated granite.' 



It would be easy to multiply cases of the metamorphism of Silurian 

 rocks on the continent of Europe, as, for example, in Scandinavia, and in 

 the Ural Mountains, where, according to Murchison, 'by following its 

 masses upon their strike, we are assured that the same zone which in one 



