parti' 6E0L0G1 OF THE MELDOH VALLETB. 1)5- 



fragment has been broken, and the parts separated by an invasion. 

 of the ground-mass. 



The included fragments in all these rocks vary much in size,, 

 from microscopic to some inches in diameter (shale-fragments may 

 be (i inches or more in length). They also vary greatly in number: 

 sometimes they are absent, in which case the rock has a subcom 

 choidal fracture, sometimes they overshadow the ground-mass. 

 Variation in this respect is extremely irregular, it is as marked along 

 the strike as across the strike. Thus 71-7o varies from line-grained 

 at 75, with no visible fragments except shale, to a coarse agglomerate 

 at 7 I with many igneous fragments; the offshoot 15-78 is Hue- 

 grained, but with large shale-inclusions. The northern margin at 

 ") I is quite homogeneous, but at 5-5 both shale and igneous inclusions 

 are found. None of the igneous fragments are other than can be 

 matched from the ground-mass of the dark igneous rock itself, or 

 from rocks found in situ in contact with the dark igneous rock- 

 It is true that one vesicular inclusion has been found (R.N.W., 

 Meldon B) in a slide from the 71 75 exposure, and as yet no 

 instance of vesicles in the ground-mass is known. But vesicular 

 patches in dyke-rocks are not uncommon, one such having been 

 discovered in dolerite from 82-84. This vesicular inclusion 

 | R.N.W., Meldon B) has a ground of felted felspar-laths, in which, 

 arc set felspar-phenocrysts of the type characteristic of the 'dark 

 igneous ' series. The vesicles are all filled, the larger with quartz, 

 in which there are usually blades of warm-sepia mica, the smaller 

 apparently wholly with mica. Some have a border of mica and a, 

 kernel of quartz. There are others in which anthophyllite, springing 

 from the wall of the vesicle, has deeply penetrated the quartz. 



Excepting these fragments of its own substance, the only other 

 igneous rock enclosed in the ; dark igneous ' is the micropegmatite- 

 felsite before described. At LXXVI, S.E. 25, near Forest Mine, 

 this felsite is in contact with the 'dark igneous' rocks, and frag- 

 ments of it are common as inclusions in the latter. 



The included fragments of sedimentary rock are recognizably 

 derived from the adjacent shales, with the contact-forms of which 

 they can be matched, except for the more intense alteration 

 which the smaller inclusions have undergone. The derivation of 

 the fragments from the rock forming the walls of the dykes or sills 

 is especially clear whereas at LXXVI, S.E. 77. these are radio- 

 larian cherts. The more ordinary shales are largely altered to 

 quartz-mosaic, and mica, either brown or greenish brown, is fre- 

 quently developed, while anthophyllite also occurs. There i- 

 sometimes developed a dusty black pigment of undetermined 

 nature. The shale-inclusions show signs of marked softening : in 

 LXXVI, S.E. 59, a felspar of the 'dark igneous' rock has indented 

 itself into such an inclusion. Slid-' LXXVI. S.E. L5, is especially 

 notable for the manner whereby the shale-inclusions, in which 

 anthophyllite is freely developed, have been softened, squeezed to 

 conform to their surroundings, and drawn out to wisps at their 

 extremities. The deformation is more marked, in that at the 



