I860.] GEIKIE OLD RED SANDSTONE. 315 



undulating region in which lies the valley of the Clyde. The narrow- 

 ness of the band at Lesmahago arises from the southward prolong- 

 ation of the great Lanarkshire coal-field, and from the northward 

 extension of the smaller coal-field of Douglas. That these two 

 coal-fields were at one time connected down the valley of the Nethan, 

 and that thus a continuous band of Carboniferous strata stretched 

 away north from Douglas to beyond Glasgow, can hardly, I think, 

 be doubted ; and this circumstance becomes of the highest import- 

 ance in any endeavour to ascertain the true relation of the Carbo- 

 niferous to the Lower Old Red Sandstone throughout the south of 

 Scotland. 



In the Birkenhead Bum, the Logan AVater, the Blaeberry Burn, 

 and the Greenock Water, there is a clear passage of the green Silu- 

 rian shales into the red shales, sandstones, and conglomerate-bands of 

 the Old lied series. That series dips regularly away from the Silu- 

 rian axis of JSutberry and Priesthill on the north and north-west 

 sides. On the east side, however, as already remarked, the succes- 

 sion is not quite so clear, owing to a fault which throws down the 

 red sandstones against a low part of the Silurian series. This fault 

 seems to increase in the amount of throw as it passes to the south- 

 west. It appears to be overlapped by another tongue of Carboni- 

 ferous rocks forming the north-eastern prolongation of the Muirkirk 

 coal-field*. Starting, however, from the section on the Logan 

 Water, where the whole succession is very clear, and passing north- 

 eastward by Lesmahago to the Clyde, we find the purplish-grey 

 sandstones which form the whole of that tract dipping almost uni- 

 formly E. by N. at from 25° to 45°. There is thus an ascending 

 series for eight miles, the total thickness of which must be at least 

 1 2,000 feet, and is probably more. Again, along the north flank of 

 the Haughshaw Hills, which consist of the same sandstones, the dip 

 is still easterly. Their south flank is obscured by another faidt, 

 which has tilted on end both the Old Bed and the Carboniferous 

 beds. In the middle of the hills the Silurian shales come up in an 

 anticlinal bend as at Xutberry Hill, and are well shown along the 

 sides of the reservoir at Parishholm, and also in the Lower pari oi 

 the Parishholm Burn. The axis which they form seems to run on 

 the east Bide of that streamlet, and nearly parallel to it. Hut the 

 Old Red and Silurian strata in this part of the district are inueh 



disturbed. As we ascend the stream, the sandstones and shales near 

 the base of the old Bed become twisted, vertical, and broken, and 

 this character continues until the whole passes under a thick uncon- 

 formable series of white fjarboniferous sandstones forming the creel 

 of the Cairn Table ridge, and dipping W. by X. at 12P—20 . 



Viewed as a whole, therefore, we have in the Lesmahago district 



two X.K. and B.W. Silurian BXeB, each with an encircling SOUS of 



Lower Old Bed Sandstone. Their south-western prolongation is 

 hidden by Carboniferous strata : while towards the north-easi they 



* Without a re-examination of ilii- pari of the district) I am unable I 

 decddedl] whether the Carboniferous rocka lure overlap the older strata, or an 

 Faulted against them. At present I incline to the former opinion. 



