ASSOCIATED ROCKS OF THE LIZARD DISTRICT. 903 



often be easy to suppose the latter intrusive in the former. Care- 

 ful examination, however, will show that there is no doubt as to 

 their true relations. The serpentine is generally much decomposed. 



On the western side of the headland the gabbro extends for some 

 distance along the shore. I was unable to examine closely its 

 junction with the main mass of the serpentine; it appeared, how- 

 ever, to be, as usual, intrusive. A small shallow gully just on this 

 side of the actual headland affords the best study of the gabbro, 

 which might be mistaken for a metamorphic rock. The schistose 

 structure strikes about N. and S., extending in considerable perfec- 

 tion over a space about 5-6 yards broad, and dips to the eastern 

 side at an angle of about 80°. It is, however, quite impossible to 

 draw any line of demarcation between the foliated and the ordinary 

 (rather coarsely) crystalline gabbro. This consists of a purplish- 

 grey plagioclase felspar, probably labradorite, often mixed up with 

 a dead-yellowish- white felspar (the saussuritic variety already 

 mentioned), which of course predominates on exposed surfaces, 

 crystals of brownish diallage, often about \ inch across, and having a 

 metalloidal lustre, and a considerable, but variable, quantity of the 

 minute rather dark green hornblende already described. In short, 

 the process of alteration from an augitic to a hornblendic rock has 

 taken place here as at the Balk ; and specimens may be found in almost 

 every stage. Not seldom the diallage seems to be entirely replaced 

 by these pseudomorphs. In some of the most schistose varieties the 

 dark " e}"es " of this hornblende remind one in appearance of the 

 spots in the Knotenschiefer. 



The two minerals (the felspar and diallage, or hornblende) are 

 often quite separated in alternating bands, those of felspar being 

 from nearly ^ inch downwards to mere lines. Not seldom the 

 diallage predominates, felspar only occurring in very thin threads, 

 with occasional " eyes " as described above. From such specimens 

 we pass to normal coarse gabbro — a variety in which the plates of 

 the diallagoid mineral are wavy in outline, and tend to be parallel, 

 being very common. 



Among the most schistose varieties lenticular pieces and long 

 slab-like masses of included serpentine are very abundant, and may 

 not improbably have contributed to the development of the structure, 

 as at the Balk. 



I have had two sections cut from the gabbro of Karak Clews. 

 The normal rock consists now chiefly of short broad rather irre- 

 gular crystals of partly altered plagioclase, with numerous microliths 

 and aggregated small crystals of pseudomorphous actinolite. Here 

 and there, however, portions of plagioclase crystals still remain but 

 little altered, as well as crystals of diallage in which the change to 

 hornblende has not been completed. Every stage of the change 

 from plagioclase to the saussuritic mineral can be traced in various 

 parts of the slide. There are occasional microliths and larger 

 grains of magnetite ; and one or two of the diallage crystals are 

 filled with an opaque black dust, the result of decomposition. These 



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