MR MILNE ON THE MID-LOTHIAN AND EAST-LOTHIAN COAL-FIELDS. 269 



(2.) It is unnecessary to say much in regard to the internal structure or com- 

 position of the limestone strata. They have all the dull and argillaceous appear- 

 ance common to the limestones of the coal-measures, without the least symptoms 

 of crystalline structure. 



There are the same sets of fissures in limestone as in coal. But they are by 

 no means so numerous. It is impossible to find a piece of cubical coal at the pit 

 mouth free fi'om fissures ; — whereas large blocks of limestone are quarried with- 

 out fissures. The principal fissures in limestone are distinguished from those in 

 the coal by being more open, and by frequently having their sides covered with 

 cup-shaped cavities. These are hollows in the rock, and are generally from 1 inch 

 to 2 inches in diameter, and about half an inch to 1 inch in depth. The sides of 

 a fissure in all other rocks are generally smooth. These fissures, when near the 

 surface, are generally fiUed with clay and various debris ; at greater depths, they 

 contain veins of calcareous spar. 



With regard to the texture and composition of the limestone, aU who have 

 read Dr Hibbert's paper on the Burdiehouse limestone must be aware, that a 

 great difference exists, in these respects, in the limestone strata of the district. 

 The Burdiehouse limestone is slaty in its structure, whilst the Gilmerton, Coldcoat, 

 and superior strata, are solid and massive. After the former has been in the 

 kiln, it can be easily separated or split, even with the hand, into thin plates. 

 This peculiarity of structure appears to be owing to the abundance of vegetable 

 and carbonaceous matter in the Burdiehouse limestone, and which is generally 

 situated between its lamina. The nature and names of the vegetables found in that 

 deposit have been so fully stated by Dr Hibbert, that it would be presumptuous 

 for me to touch upon that subject : and for the same reason, I refrain from allud- 

 ing to the discovery in it of the fishes' teeth, scales, and spines, which Dr Hibbert 

 has so fully and ably noticed. In the superior limestone strata, none of these 

 fossils have been discovered : the only fossils known in them are marine shells 

 and zoophytes. There are no vegetable impressions in these upper strata. 



(3.) In regard to the argillaceous strata of the district, the only interest at- 

 taching to them in respect of composition or internal structure, arises from the 

 fire-clay and ironstone they contain. 



That they vary in thickness and in composition, like the other strata pre- 

 viously mentioned, is undoubted ; but I am unable to state the amount or the 

 direction, or the exact nature of that variation. 



In truth, none of these strata have been worked so extensively as the coal 

 and lime strata, so that there are not the same means of obtaining information 

 regarding them. No attempt whatever has been made in the district to work 

 ironstone, though in some places it has been ascertained to be in considerable 

 quantity, and of good quality. This valuable ore occurs in two states, viz. in a 

 continuous stratum (termed " black band"), and also in small nodules or leiiticu- 



