T1IK ARCHAEAN IIOCKS 43 



large intrusive masses or bosses of granite. Tin- -tnititit-d aeries bait 

 been called the Grampian Series by Dr. Hicks 7 (1883) and the 

 Dalradian by Sir A. Geikie 8 (1891). 



The mapping of this extensive area by the Geological Survey 

 lias been in progress for many years, and reports on successive 

 portions have been published in the annual "Summaries of Progress." 

 From these we learn that the successive belts of altered stratified 

 rocks are not difficult to follow, but that> owing to the iH linal 

 folding and the intense plication, it is not easy to unravel the true 

 succession from oldest to newest. In Argyllshire, however, where 

 the metamorphism is less and the physical structure less complicated, 

 the succession appears to be as follows, according to E. B. Bailey," 

 though it is not yet known whether it should be read upwards or 

 downward.-. 



9. Eilde flags. 



8. Glen Coe quartzite (white and tine-grained). 



7. Leven schists, grey phyllites, and others with miartzite bands. 



6. Ballachulish limestone and black slates ( = Easaale slates). 



5. Striped Transition Series (not always present). 



4. Appin and Loch Awe quartzite (a pebbly rock). 



3. Appin limestone (cream coloured). 



2. Appin phyllites, with bands of flaggy quartzitr. 



1. Cuil Bay slates (black). 



The section (Fig. 4) represents Mr. Bailey's theory of the arrange- 

 ment of these groups in a series of recumbent folds, and from it 

 the reader will understand the difficulty of ascertaining the real 

 order of succession. 



With regard to the total thickness of these groups no exact 

 measurements have been made, but Mr. Bailey states that "even 

 the thinnest of them, the Appin limestone, is probably not leas 

 than 100 feet thick, while the Leven schists, Glen Coe quartzite, and 

 Eilde flags must each of them reach about 1000 feet ; the other 

 members of the sequence should doubtless be reckoned in hundreds of 

 feet. These rough estimates refer to original thickness of deposition. 

 Now over wide areas various groups are reduced to mere films, . . . 

 elsewhere again their dimensions have been mightily increased by 

 reduplication." We may infer, therefore, that the whole seriea, 

 exclusive of the Eilde flags, must have been originally between 

 4000 and 5000 feet thick at least. 



The Appin quartzite is specially interesting because what may 

 be its base is generally a pebble-bed or conglomerate ; moreover, 

 the Appin limestone sometimes passes through a pebbly calcareous 

 rock into the quartzite, so that the evidence of superposition is 

 doubtful. The pebbles are chiefly of quartz and pink felspar. In 

 other parts of the Highlands what seems to 1* the same quarUite 



