EXPLANATION OF THE PLATES. 



PLATES 10, 10*. 

 Sectional views along the N. E. coast of Ireland, 



PLATE 11. 



Sectional views of Kenbaan head and bay, on a larger scale than in the former' 

 plate. 



PLATE 12. 



Ground plan and section of Birch-hill colliery, near Walsall, Staffordshire. 



PLATE 13. 



Map of Glen Tilt. 

 The Map exhibits the general appearance of the rocks which are visible at the 

 surface. These are distinguished by colours, of which an explanation is 

 given in the margin. I may remark that the same colours are used to 

 represent the same substances throughout the whole of the plates belong- 

 ing to this paper. 



The Map does not pretend to give every rock which conies to the sur- 

 face, since the spaces wliich many of them occupy are so small as to have 

 rendered such a detail impracticable. I have omitted particularly many 

 of the small masses of quartz rock which are visible on the granite, as they 

 would, instead of elucidating, have obscured the explanation which this 

 map is designed to give. The southern side being of a more simple con- 

 struction admitted of a more real detail, yet in this also I have not pre- 

 tended to lay down the perpetual and often minute alternations of the 

 schistose rocks with the limestone, since there would not have been room 

 for this purpose : I have contented myself with indicating them in a ge- 

 neral way. 



In the method used in colouring, I have defined each colour in those 

 places where the rocks themselves are visibly defined. Where these 

 boundaries are uncertain from the covering of soil or other causes, the 

 colours are undefined. The uncoloured parts which lie near the river are 

 intended to represent the alluvial matter, although there is little doubt 

 that the junction of the limestone and the granite exists below it. I have 

 detailed as well as I could the several points where that junction is actually 

 visible : greater accuracy would have been impracticable on the map which 

 1 was obliged to make use of, with wliich my own measurements were often 

 at variance. But it is a matter of no moment for the purposes of this paper, 

 since its object will be equally accomplished whether there are twelve or 

 thirteen junctions visible, or whether Forest lodge is three or four miles 

 from Gow's bridge. I have only marked one or two masses of porphyry, 

 as a knowledge of their places was of no moment. 



