TRANSACTIONS OF SECTION C. 63 S 



stone age, but nearly the whole of tlie varied igneous rocks of the island must 

 now be assigned to the Tertiary period, not excepting the well-known granite mass 

 of the northern part of the island. The finer granite which occupies tlie interior 

 of the nucleus has a tortuous boundary. It is clearly intrusive in the coarse 

 granite which surrounds it, but both belong practically to the same period, as they 

 have one and the same system of jointing. 



The ring of granite, granophyre, and quartz diorite which surrounds the large 

 volcanic vent was previously little known, and the other numerous and varied 

 intrusive masses, both acid, and basic, which occur in the island were but poorly 

 represented on existing maps. 



2. On Variation in the Strata in the Eastern Highlands. 

 By George Barrow, H.M. Geological Survey. 



[Communicated by permission of the Director of the Geological Survey.] 



In mapping the group of rocks associated with the well-known Quartzite and 

 Limestone in the Eastern Highlands, it has been found that there is an incessant 

 variation in the lithological characters of the group, which is sometimes abrupt. 

 Detailed examination has shown that throughout that belt the same type of 

 section or succession reappears after passing a number of variations. 



The phenomena are supposed by the author to be due to the strata having 

 been deposited by numerous branches of a large river flowing through a delta. 

 Each branch, by a natural process of fanning, deposits sand near its mouth, and 

 finer mud further seawards. Where the fans of sand are far apart, the tine mud 

 deposited between them will assume a fairly constant composition, because all 

 the streams tap a common source of material before the river divides into branches 

 in the delta. 



The recurrence of one particular type of section, which is easily recognised in 

 the field, may be explained by the supposition that the materials of which the 

 strata are composed were laid down as mud or other fine sediment, which may 

 be readily detected bj* means of the special minerals present, when the rocks are 

 metamorphosed. The abruptness of the changes seen in the sections may be due 

 to the intense folding of the Highland rocks ; for materials originally some little 

 distance apart are brought into close proximity, and the transition which once 

 existed is cut out at the surface by the folding. 



3. On the Crystalline Schists of the Southern Highlands. Their Physical 

 Structure and its Probable Manner of Development. By Peter 

 Macnair. 



The area under notice is defined as that lying immediately to the north-west 

 of the great boundary fault which crosses Scotland from the Firth of Clyde to 

 Stonehaven. An account is then given of the various opinions that have been 

 held concerning the structure of this region since the time of MaccuUoch up to 

 the present day. The author then proceeds to show that the schist zones traverse 

 this region in roughly parallel bands, and described a series of sections at right 

 angles to the strike of the principal foliation of the area. The following is a 

 summary of his conclusions regarding the stratigraphy, physical structure, and the 

 manner of its development in this part of the Scottish Highlands : — 



1. The sedimentary schists of the Highlands proceeding from the margin 

 inwards may be divided into the following zones: — Lower Argillaceous zone. 

 Lower Arenaceous zone, Loch Tay Limestone zone, Garnetiferous Schist zone, 

 Upper Argillaceous zone, Upper Arenaceous zone. Associated with these are 

 schists of igneous origin. It is probable that these zones are capable of still 

 further subdivision, but this is not attempted yet. 



2. From an examination of the relationships of these different zones, the order 



