1855.] 



MURCHISON LESMAHAGO SILURIANS. 



17 



be connected upon the surface with 

 those of the tracts around the Lead 

 Hills and other parts of Ayrshire 

 and Dumfriesshire, on the S. and 

 S.E., must be a work of future la- 

 bour. That work will demonstrate 

 whether these Lesmahago rocks 

 constitute an advanced Silurian 

 promontory or headland, or whe- 

 ther, as is most probable, they form 

 an outlier of that age. 



The large parish of Lesmahago 

 is pre-eminently distinguished in its 

 western part by dome-shaped hills, 

 which rise to the S.W. of the River 

 Clyde, and on the left bank of that 

 river, where it forms the well-known 

 beautiful Falls of Bonnington and 

 Stonebyres, near the town of La- 

 nark. The rock over which the 

 Clyde cascades is the Old Red 

 Sandstone, which formation, ex- 

 tending to the W. and S.W. to the 

 village and parish of Lesmahago, is 

 overlaid on the north and south by 

 carboniferous limestones and coal ; 

 whilst on the south-west it is un- 

 derlaid by the dark and schistose 

 rocks to which attention is now 

 specially invited. 



Upper Silurian Rocks. — The re- 

 lations of these dark grey, schistose 

 strata of clay- slate to the Old Red 

 Sandstone are seen on the banks of 

 the Nethan River and also on those 

 of other tributaries of the Clyde, 

 particularly the Logan Water, on 

 each of which rivers Mr. Slimon 

 has marked the junction between 

 the grey Silurian and the Old Red 

 rocks. The Silurian beds rise up 

 into several hills of considerable 

 altitude, one of which (Nutberry, 

 1715 feet above the sea) we as- 

 cended. Judging from the outline 

 of the country, and the exten- 

 sive range of similar high moor- 

 lands, I am disposed to think that 

 these rocks may be found to spread 

 north and westward over the hills 



VOL. XII. PART I. 



m <o 



