138 MR J. D. FALCONER ON THE 



constituent frequently appears in beautiful branching forms, the fibres being of consider- 

 able length and variously curved, while the felspars are much elongated, striated, or 

 unstriated, and more rarely slightly bent. The lighter and darker coloured varieties are 

 frequently associated irregularly in the same specimen, and sometimes the association is 

 so intimate as to give rise to a spotted appearance in the rock. Variations in texture 

 are sometimes to be observed, and occasionally very coarse-grained patches are found, 

 frequently exhibiting a central cavity which may be filled with calcite, chlorite, or 

 quartz, or with water, clear mineral oil, brown solid paraffines, or black viscous pitch. 

 Such cavernous knots are met with from time to time in the Linlithgow quarries, and 

 are to all intents and purposes druses, probably originating through concentration of 

 steam at various points within the cooling mass, and a consequent slower crystallisation 

 in the surrounding maoma. The rocks weather with a brown crust, and crumble into a 

 coarse felspathic sand. 



The dykes and sills pass marginally into fine-grained blue aphanites, which, at a 

 distance of 2-6 ft. from the junction, may develop a spotted appearance, investigated 

 below. The spots are dark green, and sometimes weather out as knots on the exposed 

 surface, being more resistant than the surrounding rock. Nearer the junction vacuoles 

 and amygdules are abundant, the latter sometimes elongated at right angles to the 

 plane of contact. At the junction the rock assumes a fine-grained basaltic character, 

 usually porphyritic with scattered felspars, ferromagnesians, and pyrites. Glassy 

 modifications have not been observed. 



The larger sills, as exposed in the Kettlestoun and Carribber quarries, are crossed 

 by irregular contemporaneous veins of two varieties : (1) blue and fine-grained. (2) pink 

 and coarse or fine in grain ; known locally as " blue-band " and " iron-band " re- 

 spectively. Sometimes fragments of the coarser rock are enclosed in the veins as if 

 some slight brecciation had occurred in places. The veins, however, are never sharply 

 marked off by chilled edges from the surrounding rock, their material passing, as a rule, 

 quite gradually into the intersertal material of the host. 



Contact metamorphism is rarely seen, probably from the absence of exposures. 

 Here and there, shales and sandstones are baked and hardened, but with no obvious 

 new formation of minerals other than pyrites. In Carribber Glen, a calcareous rock, 

 interbedded with ash, has been completely metamorphosed into a blue crystalline 

 granular limestone, with abundant production of colourless transparent garnets in a 

 matrix of calcite, chlorite, and chalcedony. 



MlNERALOGICAL CHARACTERS OF THE DlABASES. 



In the felspars, a columnar habit is general throughout, the crystals being elongated 

 on the "a" axis with equal development of 001 and 010. The length varies consider- 

 ably, the maximum being obtained in the lighter coloured portions of the larger sills. 

 In section the brachypinacoids are usually sharply defined ; frequently, however, the 

 terminations, and occasionally also the basal planes, are imperfectly marked off from the 



