128 BATHYMETRICAL SURVEY OF 



NOTES ON THE GEOLOGY OF THE TAY BASIN. 



By B. N. PEACH, LL.D., F.R.S., and J. HORNE, LL.D., F.R.S. With 

 Geological Map (Plate XXXIV.). Published by permission of the 

 Director of H.M. Geological Survey. 



The Tay basin may be divided geologically into two parts, the 

 boundary between the two being denned by the great fault along the 

 Highland border which runs from Glen Artney, by Crieff , Murthly, and 

 Blairgowrie, towards Cortachy and Stonehaven. The area north-west 

 of this line is mainly occupied by the metamorphic rocks of the Eastern 

 Highlands, which are pierced by masses of granite, diorite, and other 

 igneous intrusions, the latter being of special importance in connection 

 with the history of the glaciation of the region. In the western part of 

 the metamorphic area, on the lofty peaks of the Black Mount forest, 

 there is a remnant of the contemporaneous volcanic rocks of Lower Old 

 Red Sandstone Age, which are so prominently developed in the Lome 

 plateau. The tract, south-east of the Highland fault, embraces the 

 lower and smaller portion of the Tay basin. With the exception of a 

 small patch of Carboniferous strata near Bridge of Earn, the whole of 

 this tract is occupied by rocks of Old Red Sandstone age. 



In connection with the Lake Survey, the area north-west of the 

 Highland fault is of special interest, as it includes most of the lochs 

 which have been sounded by the staff. The metamorphic rocks which 

 floor the greater part of this tract are bounded on their south-east 

 margin, for a considerable distance, by the great dislocation along the 

 Highland border. Indeed, the fault-line in places gives rise to a 

 prominent feature, and the change, in the geological formations on 

 either side, is indicated by a marked difference in the topography. The 

 age of the metamorphic rocks of the Eastern Highlands has not 

 been definitely fixed, and the original sequence of deposition is still 

 uncertain, but they have been arranged in certain groups, which appear 

 in a definite order as the observer proceeds northwards from the border 

 fault. 



Apart from the crystalline schists termed the " Moine Series " by 

 the Geological Survey, which occur in the northern part of the area, 

 the groups of metamorphic strata met with in the Tay basin are given 

 in the subjoined table : 



11. Quartzite and quartz-schist with pebbly conglomerate and 



boulder bed. 

 10. Blair Atholl limestone. 



9. Black schist with thin limestone bands. 



8. Calc-sericite schists and phyllites. 





