at 
VEL. 
ON THE VARIOLITE AND ASSOCIATED IGNEOUS ROCKS OF 
ROUNDWOOD, CO. WICKLOW. By PROFESSOR W. J. 
SOLLAS, LL.D., D.&c., F.B.S. 
[Read DeceMBER 21; Received for publication DEcemBER 22, 1892; Published 
Marcu 25, 1893.] 
In glassy rocks, consolidating under certain conditions, one of 
which is a somewhat rapid rate of cooling, a radiate growth of 
erystals about scattered centres is frequently set up, leading in 
many cases to the formation of crystalline spheres with a radiate 
structure. In rocks containing a large proportion of silica, such as 
rhyolites (obsidian), geologists have long been familiar with this 
spherulitic structure ; but in basic rocks or those poor in silica, 
such as glassy basalts, its existence has been questioned or denied : 
and yet under the name of variolite, basic rocks presenting the 
spherulitic structure in all its details have long been known and 
frequently described. Their true nature was, however, not at first re- 
cognized, and itis only in comparatively recent times that they have 
received a full and complete explanation. A learned account of 
the views which have from time to time been held on this subject 
has been given by Professor Cole and Mr. Gregory,! and I need 
only add to the long list of Papers cited by them one by Dathe,* 
which is of interest as confirming by anticipation some of their 
views, and another by Lossen,* whose remarks, though short, are 
characteristically to the point. Professor Cole has recently added 
to our knowledge of this subject by Papers read before this Society, 
1«On the Variolitic Rocks of Mont Genévre,’’ by G. A. J. Cole and J. W. Gregory, 
Quart. Journ. Geol. Soc., vol. xlvi., p. 295 (1890) ; and “‘On the Variolitic Diabase 
of the Fichtelgebirge,”’ by J. W. Gregory, id, vol. xlvii., p. 45 (1891). 
2 “ Dathe, Beitrage z. Kenntniss der Diabase-mandelstaine,’’ J. B. d. K. Preussichen 
geologischen Landesanstalt u. Bergakademie, p. 410 (1884). 
3 Lossen, Geologische u. Petrographische Beitrage z. Kembriss des Harzes, ib., p. 7 
(1881). 
