490 



J. J. S. Teall — Origin of landed Gneisses. 



is about 3-05. With regard to the so-called saussurite, I am able to 

 state that malacolite, felspar, and minute granules of sphene often 

 occur as constituents. The malacolite has been isolated and analyzed 

 by myself, so that no doubt exists as to its identification, though it 

 often occurs only in minute grains without form or cleavages. The 

 doubtful substance which appears white by reflected and brown by 

 transmitted light and which is a constant feature in the Lizard 

 saussurite has not been identified. 



Fig. 3. 



We have now to consider the mutual relations of the different 

 rocks above described. At Kennack Cove and at Pen Voose, near 

 Landewednack, granite may be seen veining diorite, often in the 

 most intricate manner (see Fig. 1, Plate XIV.). At Pen Voose, 

 veins of both granite and diorite occur in the gabbro, Fig. 4. The 

 three rocks are therefore of igneous origin. They exhibit the 

 relations of igneous rocks, and they possess the composition of 

 igneous rocks; moreover, it is possible to find here and there portions 

 which have escaped the influence of the dynamic metamorphism, 

 and which show the normal structure of igneous rocks. But the 

 same rock types occur as integral portions of a banded gneissic 

 series in the same localities. The bands are in some places as re- 

 gular as layers of sediment in a stratified rock-mass, in other places 

 they are crumpled and contorted (Fig. 3) ; in others we observe 

 " eyes " and lenticles of diorite surrounded by streaks and bands 

 of a granitic rock (see Fig. 2, Plate XIV.) 



As a rule the banded gneissic series is formed only of granitic 

 and dioritic rocks, but we occasionally find eyes and streaks of 

 gabbro and gabbro- schist. One large specimen, to which I wish to 

 direct special attention, shows a crumpled band of gabbro-schist in 

 mica-diorite. 



Another mass much too large to carry away showed the appearance 



