438 Geological Society : — 



any fairly small temporary load (say not exceeding one tenth the 

 breaking-load) until the elongation which is produced on putting 

 on the load is equal to the contraction which ensues on taking 

 it off, and the ratio of the temporary stress to the temporary 

 strain then produced be taken as measuring Young's modulus, we 

 obtain a result which is practically the same as when the deforma- 

 tion is infinitesimal, one which is independent of the amount of 

 permanent load and, provided in the case of iron and steel which 

 have been permanently deformed rest be allowed, one which is 

 independent of any previous permanent extension of the metal. 



There is a slight slip in putting — for Poisson's ratio on p. 20 



and m for the same ratio on p. 253, but on the whole the book has 

 evidently been written with great care ; and we heartily congratu- 

 late Professor Unwin on having produced a work which is emi- 

 nently adapted for the purpose for which it is intended, namely, 

 to be a text-book for the engineering laboratory. 



The book is copiously illustrated, and is in every respect well 

 worth its price, 21s. 



LV. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 322.] 



March 14, 1888.— W. T. Blanford, LL.D., F.R.S., President, 

 in the Chair. 



'TVEE following communications were read : — 



-*~ 1. " On the Gneissic Rocks off the Lizard." By Howard Fox, 



Esq., F.G.S. ; with Notes on Specimens by J. J. H. Teall, Esq., 



F.G.S. 



The rocks may be classed under three heads : — (i.) the coarse 

 gneisses or Men Hyr type, (ii.) the light-banded granulitic gneisses 

 or Wiltshire type, and (iii.) the transition micaceous rocks of : ' Lab- 

 ham Reefs," type intermediate between (ii.) and the mainland 

 schists. 



The first are seen in Mulvin, Taylor's Rock, Man-of-war Rocks, 

 the Stags, Men Par, Clidgas, Men Hyr, and Vasiler ; the second in 

 Sanspareil, the Quadrant, and adjoining reefs, Labhaut Rocks, &c. ; 

 and the third in the Labham reefs. 



The* inclination of the divisional planes appeared conformable 

 with that of the rocks of the mainland. 



The gneisses and granulites of several of the islands are traversed 

 by numerous dykes of porphyritic basic rock, seen in Taylor's Rock, 

 Man-of-war Rocks, Sanspareil, Quadrant Rock and Shoals, and Clid- 

 gas. These dykes have been disturbed by movements subsequent 

 to their intrusion. They sometimes strike across the foliation- 

 planes of the gneiss and send veius into the latter rock ; at other 



