Vol. 50.] ANNIVERSARY ADDRESS OF THE PRESIDENT. 1 25 



Messrs. Cole and Gregory tell us that the variolite of the Durance 

 occurs in situ as a selvage on the surface of certain diahases, also 

 as blocks in the associated fragmental rocks which are apparently 

 tuffs, and occasionally as a selvage to diabase-dykes. This product 

 of rapid cooling was originally a spherulitic tachylyte, and has 

 become devitrified by slow secondary action. In fact, they say that 

 variolite stands in the same relation to basic lavas as pyromeride 

 does to those of an acid character. These eruptive rocks are 

 probably of post-Carboniferous age, and there are several other 

 areas of similar variolitic rocks both in the Alps and the Apennines. 

 The best modern representative of the conditions that produced 

 such rocks is to be found in the great volcanoes of Hawaii. 



In the succeeding volume of the Quarterly Journal Mr. Gregory 

 gave the results of his examination of the variolitic diabase of the 

 Fichtelgebirge as deduced from the neighbourhood of Berneck. This, 

 he concludes, is intrusive into rocks of Devonian age. The variolitic 

 structure is found to occur in two different arrangements, viz. : — 

 on the surface of spheroidal masses of compact diabase ; and, secondly, 

 as a true contact-product on the selvage of the diabase, the varioles 

 being true spherulites. He also concluded that, although the 

 varioles are the product of rapid cooling, too sudden a solidification 

 of the diabase may prevent their formation. 



Returning now to the consideration of Miss Raisin's paper on the 

 Variolite of the Lleyn, it would appear that the first discovery of 

 this rock in Britain was made by Prof. Blake at Careg Gwladys in 

 Anglesey, as announced at the meeting of the British Association in 

 1888. 1 Subsequently Prof. Cole described a rock of this description 

 from Annalong, in the county Down. 2 According to the statement 

 of Prof. Bonney, Miss Raisin's discovery of Variolite at the Lleyn 

 affords the third example of this kind of rock in the British Isles. 

 The specimens described by that lady occur at Aberdaron, and also 

 at one or two localities on the west coast of the Lleyn in a district 

 which was marked on the Survey Map as ' Metamorphosed Cam- 

 brian.' Amongst the rock-specimens not hitherto described, Miss 

 Raisin includes forms of variolite, a spherulitic, somewhat basic 

 rock. The igneous masses which contain these are stated to belong 

 to the class of rather basic andesites, or not very basic basalts : 

 corresponding to these two types of rock are two forms of variolite. 

 Their general microscopic structure and development are described 



1 Brit. Assoc. Rep'. 1888 (Bath Meeting), p. 411, pi. v. fig. 22. 



2 Sci. Proc. Roy. Dub. Soc. vol. vii. (1892) p. 513. 



