004 T. 0. BONNET ON THE SERPENTINE AND 



have some resemblance to certain hypersthenes ; but the mineral does 

 not belong to the orthorhrombic system. There is a general banded 

 structure shown in the arrangement of the minerals. 



The second slide is cut from a pale-coloured, apparently imper- 

 fectly crystallized rock, consisting chiefly of two minerals — the 

 principal a whitish or pale pinkish felspathic one, the other a pale 

 green mineral. The former, under the microscope, when examined 

 with polarized and analyzed light, assumes the characteristic granular 

 aspect of the saussuritic pseudomorph after plagioclase. The other 

 mineral appears to be an almost colourless augite, containing a 

 large number of very minute microiiths. There are but slight in- 

 dications of seconda^ hornblende. Some small roundish white 

 specks, just visible to the eye, in the felspathic portion of the rock, 

 appear, under the microscope, as rather oval blotches, often opaque 

 and brownish, but in other cases showing aggregate polarization of 

 a somewhat fibrous mineral, with colours from a rather orange 

 yellow to a purplish blue, probably one of the zeolites. This rock 

 also shows a banded structure. 



On the eastern side of the headland we come at once on the 

 serpentine as the predominant rock, though it is broken through by 

 many veins of coarse gabbro. The mineral composition of these 

 resembles that just described. Some are of considerable thickness ; 

 but others die away as mere strings. The material of the gabbro, 

 therefore, must have been injected in a very fluid condition, and, as 

 even the strings are coarsely crystalline, must have made its way into 

 rock of high temperature, and have cooled down very slowly. The 

 larger masses more frequently exhibit a schistose structure than 

 these finer veins, though they are sometimes quite without it. 

 Every stage may be noticed here as on the other side of the head- 

 land. Here, also, the " eyes " of hornblende are frequently seen in 

 the schistose varieties. 



Between the headland and Lankidden Cove are several gabbro 

 veins. The serpentine is a red variety, much resembling one pre- 

 sently to be described. On approaching the Cove two or three 

 narrow greenstone dykes are seen in the cliffs, and one in a skerry 

 projecting from the sand. These cut both the serpentine and the 

 gabbro, and closely resemble those already described near Kennaek 

 Cove. A section from one exhibits plagioclase felspar in fair preser- 

 vation (the crystals commonly five or six times as long as broad, cha- 

 racteristically twinned, and mostly well defined), augite (often well 

 preserved), and some magnetite. Besides this there is in the interval 

 of the larger plagioclase crystals, a good deal of an aggregate of a 

 fibrous transparent mineral, changing, with polarized light, from 

 bright blue to yellowish or occasionally pinkish colours — doubtless a 

 pseudomorph after felspar, perhaps replacing a magma. Here and 

 there the augite changes to pale green rather fibrous hornblende, 

 showing marked dichroism, and rather rich colours with analyzer and 

 polarizer. There is also a brown dichroic mineral : some of this is 

 probably little more than a ferruginous staining ; but in one case it is 

 certainly a distinct mineral, probably an iron-mica. There is no 



