106 GEOLOGY OF THE LOTHIANS. 



limestone is to the N.W. In the old quarry of Kirkton, 

 the surface rock is a greenstone which, in some places, par- 

 takes of the characters of basalt, and frequently evinces a 

 tendency to the columnar arrangement ; it rests in its course 

 on different rocks in different parts of the quarry, in one 

 part being directly superimposed on a fine slaty tufa, com- 

 posed of a minute aggregation of wacke and trap sand, while 

 in another it is in immediate connection with a thin bed of 

 mountain-limestone which gradually wedges out at both ex- 

 tremities.* Below these thin strata of limestone, a thick bed 

 of slaty green tufa occurs, resting through the whole extent 

 of the quarry on the principal limestone stratum. (Plate 

 XII. Fig. 3.) In regard to changes in mineral character, 

 neither the tufa nor the limestone exhibit any thing marked ; 

 they are as compact at a distance from the greenstone, as 

 when in immediate contact with it ; they present however, 

 numerous flexures, and in one or two places shifts have 

 taken place in the limestone. Near the old quarry of 

 Kirkton, and almost on the same line, another opening 

 has been made, and there the same general arrangement is 

 visible ; the limestone, with its concomitant strata of slate- 

 clay and ironstone, is surmounted by the same trap and 

 green tufa, the latter of which is connected with the lime- 

 stone in the most irregular manner. The mineral cha- 

 racters of this limestone differ in some degree from the 

 other ; it abounds in contemporaneous imbedded masses of 

 hornstone, and alternates with strata composed of siliceous, 



* To those who are inclined to consider the limestone of Kirkton as of 

 fresh-water origin, from the statement of Dr Hibbert in the 13th volume 

 of the Transactions of the Royal Society of Edinburgh, u that a decidedly 

 fresh-water limestone is there exposed, which is characterized by the ab- 

 sence of all marine shells, coral, &c. ;." we may mention, that the fact of 

 its being so characterized is incorrect, inasmuch as we have found in it 

 specimens of the Productus. 



