ON THE GNEISSIC EOCKS OFF THE LIZARD. 



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24. On the Gneissic Eocks off the Lizard. By Howard Fox, Esq., 

 F.G.S. With Notes on the Specimens, by J. J. H. Teall, Esq., 

 M.A., E.G.S. (Read March 14, 1888.) 



At Mr. Teall's suggestion, I made, during the past autumn, a 

 methodical examination of the outlying rocks at the Lizard, and 

 forwarded to him series of specimens from the various rocks. They 

 may be classed under three heads : — the coarse gneisses or " Men 

 Hyr" type, the light banded granulitic gneisses or " Wiltshire " tvpe, 

 and the transition micaceous rocks of " Labham-Eeefs " type. The 

 annexed map (fig. 7, facing p. 316) shows how these rocks lie with 

 respect to each other and the mainland. The coarse gneisses compose 

 the outer rocks, and the fine gneisses the inner rocks. The transition 

 rocks associate the gneisses with the typical schists of the mainland. 



Beginning at the extreme west, we find the " Mulvin " composed 

 of a dark granulitic gneiss with a strike and dip both clearly con- 

 formable with the rocks of the Lizard Head, the strike being about 

 N.N.W. and S.S.E., the dip E.N.E. 



The " Taylor " rocks are a group of three coarse gneissic rocks. 

 The outer of these has a basic porphyritic dyke running across it 

 from the S.W. to the N.E. with a S.E. dip. This dyke varies in 

 width from one to four feet, and branches at the western end. The 

 middle or main " Taylor " rock has a small gully on its southern 

 extremity. At low-water spring-tide a basic porphyritic dyke, 

 18 inches wide, is seen to traverse this gully in an E.IST.E. and 

 W.S.W. direction, dipping S.S.E. The inner "Taylor" rock is 

 mostly composed of a coarse gneiss with some basic bands. 



The most conspicuous of the outlying rocks are the " Man-of- 

 War " series, the western end of which towers high above the sea- 

 level and is separated from the next highest, locally known as the 

 " Spire," by a cleft or gully. The annexed rough diagram, fig. 1, 



Fig. 1. — " Man-of-War " Rocks, as seen from the east. 



The black marks represent dykes. 



A. The cleft in which landing is most easily effected. 

 a is known as the " Spire." 



