229 



The section contains many crystals of quartz and a few of 

 felspar (sanidine) in a ground mass of brown glass. This glassy 

 base is of several shades of brown, and has been streaked out 

 by the flowing of the rock while still liquid. The large crystals 

 were formed previous to eruption, as it will be seen that the 

 glass flows round them. 



The ground mass is traversed by a series of roughly concentric 

 cracks, which are produced by the contraction of the material 

 when cooling. This is called " perlitic structure," and it will 

 be noticed that it occurred after the flowing ceased, as it crosses 

 the flow lines. 



Professor Watts, in the Q.J.G.S. 1894, mentions that these fine 

 perlitic cracks sometimes traverse the quartz crystals as well as 

 the glassy base. This will be seen in the crystal under the 

 microscope. 



The glassy base is crowded with minute crystals of felspar 

 and dusty material. 



The rock is very brittle and difiicult to grind. 



At the meeting of the Club held on February 28th, 1911, 

 Prof. E. A. Minchin, M.A., V.-P.Z.S., F.L.S., President, in 

 the chair, the minutes of the meeting held on January 24:th 

 were read and confirmed. 



Messrs. H. F. D. Jacob, H. Sidebottom, W. E. Bartrum, 

 H. Austin, J. Davidson, E. H. Thomas, J. Pullman and J. 

 Ritchie, jun., were balloted for and duly elected members of 

 the Club. 



The List of Donations to the Club was read and the thanks of 

 the members were voted to the donors. 



Mr. J. N. Bremner exhibited and described a " swing out " 

 substage fitting which would take the optical part of either an 

 Abbe illuminator or an achromatic condenser. The optical part 

 could be swung out and the iris diaphragm left in the optic axis 

 if desired. 



The President said that those who had the opportunity of 

 examining this piece of apparatus would no doubt agree that it 

 was not only very beautifully made, but was likely to be very 

 useful to microscopists. 



