1907-1908.] 8 1 



dust remaining suspended in the atmosphere. The size, liquidity, 

 rate of flow, and temperature of lava streams were then considered, 

 the temperature being determined by fusing wires of copper, iron, 

 and silver in the lava. Some rocks which have been produced by 

 the cooling of basic lavas show good columnar structure, as in the 

 well-known basalt of the Giant's Causeway. The cracks have 

 been produced by the shrinking of the lava on cooling, and the 

 characteristic hexagonal shape of the columns may be the result 

 of evenly-distributed tension throughout the cooling mass. Of the 

 various fragmentary materials ejected from volcanoes mention 

 might be made of pumice, which is full of steam cavities, volcanic 

 bombs, which are rounded owing to having been ejected with a 

 rotary motion, and the exceedingly fine filaments, which are 

 known as " Peles Hair." Volcanic dust may reach the ground at 

 red-hot heat and ignite combustible objects. This occurred 

 during the eruption of Martinique in 1902. The portion of the 

 lecture dealing with intrusive masses of lava was illustrated by 

 slides showing these features at Cave Hill, Scrabo Hill, and other 

 localities near Belfast. After alluding to submarine volcanic 

 action, which occurs on a vast scale, as shown by numerous 

 islands which have been produced, the lecturer concluded with 

 an account of the distribution of volcanoes, which occur on 

 submarine ridges and along the margins of ocean basins. 



The lecture was illustrated throughout by a series of beautiful 

 slides, the lantern being in the hands of Mr. A. R. Hogg, as usual. 



The lecture, which was listened to with much pleasure, was 

 followed with a discussion, in which the following members took 

 part :— The Chairman, Messrs. Robert Welch, M.R.I. A. ; Thomas 

 Anderson ; and William Gray, M.R.I. A. Mr. Dewhurst having 

 suitably replied to the various criticisms, the proceedings 

 terminated. 



