10 THE JOURNAL OF GEOLOGY. 



Durness limestones, but which have been everywhere and 

 entirely metamorphosed, remains for future discovery. For my 

 present purpose, it is sufficient to observe that, in the meantime, 

 as we can not be sure of the origin of most of the rocks, which, 

 between the West Coast and the line of the Great Glen, have 

 been subjected to a gigantic post -Cambrian regional metamor- 

 phism, it seems safest to exclude them from an enumeration of 

 the pre -Cambrian rocks of Britain. 



Dalradian. East of the line of Great Glen, which cuts the 

 Scottish Highlands in two, another group of crystalline schistose 

 rocks is largely developed. It consists mainly of what were 

 undoubtedly originally sedimentary deposits, though they are 

 now found in the form of quartzites, phyllites, graphitic schists, 

 mica-schists, marbles, and various other foliated masses. With 

 them are associated numerous eruptive" rocks, both acid and 

 basic, sometimes still massive and easily recognizable as intru- 

 sive, sometimes more or less distinctly foliated and passing into 

 different gneisses, hornblende-schists, chloritic-schists, etc. 

 Though it is not always possible in such a series of metamorphic 

 rocks to be certain of any real chronological order of succession, 

 those of the Highland tracts have now been mapped in detail over 

 so wide an area, that we are probably justified in believing that 

 a definite sequence can be established among them. These 

 masses must be many thousand feet thick. Their succession 

 and association of materials are so unlike those of any of the 

 known older Palaeozoic rocks of Britain, that they can hardly be 

 the metamorphosed equivalents of any strata which can be 

 recosfnized in an unaltered condition in these islands. Some 

 traces of annelid casts have been found in the quartzites, but 

 otherwise the whole series has remained entirely barren of 

 organic remains. 



What then is the age of this important series? I must con- 

 fess that in the meantime I can give no satisfactory answer to 

 this question. I have proposed, for the sake of distinction and 

 convenient reference, to call these rocks " Dalradian." Murchi- 

 son supposed them to be a continuation of his Durness quartzites, 



