Geological Survey of the United Kingdom. 475 



Geological Survey, and it should be more distinctly shown bow far 

 tbe observations recorded are new, or simply confirmatory of what 

 others have made known. No doubt, to a large extent, it is the 

 very detail itself which is new, but this for the most part is 

 interesting only to the geologist who knows the ground or is 

 working at it, and the greater part might perhaps profitably be kept 

 for the memoirs illustrating the maps. 



The field-work has ranged over most of the formations, with the 

 exception of Cambrian and Permian. The pre-Cambrian rocks of 

 the counties of Eoss and Inverness have received a good deal of 

 attention : they include certain displaced masses of Lewisian gneiss 

 and the schists known as the " Moine series." The "Dalradianor 

 younger schists of the Scottish Highlands " receive separate treat- 

 ment, and it is remarked that we may conveniently retain the 

 provisional name " Dalradian " for the younger schists of the region 

 east of the line of the Great Glen. If it shall be shown, as seems 

 probable, that the Moine-schists of the north-west pass into and 

 form part of the Dalradian series of the Central Highlands, a step 

 will be gained towards the solution of the problem as to the age 

 and origin of the schists of both regions. We know that the 

 Moine-schists of the north-west have been pushed into their present 

 positions, and probably have acquired their present crystalline 

 characters, since Cambrian time. The Survey has detected bands 

 of what appear to be Arenig rocks wedged in among the schists 

 and grits along the southern border of the Highlands. It thus 

 seems possible that the plication and metamorphism of the High- 

 land schists were not concluded until Lower Silurian time, and that 

 these schists may have originally consisted partly of older Paleeozoic 

 as^ well as pre-Cambrian sediments. 



In the island of Arran evidence which tends to support tho 

 above suggestions has been obtained. A strip of rooks that can 

 be separated from the ordinary schists of the island has been found 

 to be well developed in the valley known as North Glen Sannox. 

 It crosses the glen from south to north at a distance of rather more 

 than a mile from the sea. It is upwards of a mile and a half long, 

 and from 100 to 400 yards broad, having its narrower width at 

 the northern end. The rocks in this strip of ground, so far as can 

 be seen, are not separated by any structural line from the ordinary 

 schistose grits of the Highland series, which they follow with no 

 apparent break. Nor do they differ in degree of metamorphism 

 from the contiguous Highland schists. A closer examination, how- 

 ever, reveals some characteristic features which have not been met 

 with among the schists, but which precisely resemble those already 

 detected in the supposed Arenig rocks of the Highland bordei-. 

 They consist of black shales or schists and cherts, with some 

 intercalations of igneous rock, which probably include both volcanic 

 and intrusive bands. 



In the section on Silurian rocks we have some interesting 

 references to the igneous rocks, and to the establisliment of th& 

 eruptive nature of what were believed to be tuffs and agglomerates 



