ASSOCIATED IGNEOUS ROCKS OF THE AYRSHIRE COAST. 777 



wholly occupied by an imperfectly translucent ferruginous mineral 

 of burnt-sienna colour, doubtless akin to hsematite and the colouring- 

 matter of the rock. There is some calcite in a crack traversing the 

 slide, mixed possibly with a little minute dolomite ; it also occurs 

 associated with a microlithic " dust," replacing some (? pyroxenic) 

 mineral. Bronzite is present, though in small grains, and much 

 altered. 



(2) Specimen collected from rocks a little to the south of Carleton- 

 Port headland. This is a compact rock of an Indian-red colour, 

 marbled or mottled with purplish or purplish grey, in which are 

 rather rounded grains or "eyes" of a greenish mineral, apparently 

 a decomposed bronzite. Under the microscope this rock is seen to 

 be in general structure very similar to the last, but with the 

 "strings" a little more definitely parallel; to these also the coarser 

 part of the ferruginous constituent is rather more restricted, though 

 an extremely minute dust is everywhere thinly disseminated in the 

 serpentine. There is bronzite much altered, and a minute grain or 

 two of picotite (?). 



The dark serpentine from near the milestone named above is a 

 dull purplish rock indistinctly marbled with dark greyish green, 

 containing many glittering bronzitic crystals, with lustre but slightly 

 metallic. Under the microscope it shows the usual characteristic 

 ground-mass and a good many crystals of rather altered bronzite. 

 The "steatitic" veins are opaque under the microscope, and are 

 associated with a little bronzite and a fair quantity of a not very 

 well-preserved mineral, which I believe to be augite. 



Returning to the hamlet of Lendalfoot, and following the shore 

 northward to trace the serpentine, we find fresh evidence of its 

 intrusive character ; there are, however, some rocks, apparently in- 

 trusive in it, which we shall presently notice. North of the hamlet, 

 the great blocks belonging to the "dioritic" series stand up in 

 huge wall- or dyke-like masses. These are generally of a dark rock 

 resembling basalt, occasionally porphyritic, with crystals of white 

 felspar. Passing the block already noticed, near which are others 

 almost as large, we observe everywhere the same evidence. Usually 

 the serpentine may be seen in situ beneath these blocks ; it thrusts 

 a tongue or two into them and adheres to the side; the junction - 

 surface has almost always a glazed appearance. Serpentine, com- 

 monly dark-coloured and with a clean subconchoidal fracture, seems 

 generally to underlie the sand and boulders for about three quarters 

 of a mile, when we come to some remarkable intrusive rocks, which 

 we shall describe below. 



A short distance beyond these the serpentine ends abruptly against 

 a basalt dyke, on the other side of which is a dark schistose-looking 

 tuff ; and then comes the huge mass of porphyrite of Pinbain Hill. 



The Gabbros. 



These rocks, which have just been mentioned, are, as I fully 

 believe, the hyperite and diallage rocks of Dr. J. Geikie, and, so 



