290 



[Proc. B.N.F.C. 



plants ; (4) Mesophytes, intermediates. Most belong to the last 

 class. Warming's Handbook on the subject, which has now been 

 translated and published by the Clarendon Press, was recom- 

 mended as the best guide to study. 



" PETROLOGICAL TYPES OF BASALT IN CO. ANTRIM." 



The Geological Section of the Club held its first meeting for the 

 Winter Session in the Museum, on 24th November, the Chairman 

 of the Section (Mr. W. J. C. Tomlinson) presiding. A very 

 interesting communication on the petrological types of basalt in 

 County Antrim was brought before the meeting by Mr. Strachan. 



The introduction to this lecture consisted of an elementary 

 description of the rock-forming minerals constituting the Felspar- 

 Basalts of Tertiary age in Co. Antrim, and their appearance in 

 thin sections under the microscope. 



The lecturer then stated that various rock-names, such as 

 "greenstone," "diabase," and "trap" had been used in describing 

 the local basic rocks, but the two words Basalt and Dolerite were 

 quite sufficient and definite for general purposes ; the former being 

 used to include the fine-grained hypocrystalline rocks, while the 

 latter was reserved for the holocrystalline and coarser-grained 

 varieties. He then pointed out that the division of these rocks 

 into an Upper and Lower series, and the descriptive division into 

 amygdaloidal, compact, tabular, spheroidal, and columnar varieties, 

 although most useful and necessarv in field-work, was quite 

 inadequate in petrological work, where divisions were determined 

 by definite microscopical characteristics. In field-work, however, 

 a classification of rocks could often be arrived at which agreed in 

 the main with the petrological determinations, and the basaltic 

 rocks of this neighbourhood were no exception to that rule. A 

 superficial study of these rocks at once suggested a natural division 

 into two great classes, viz. : — 1st, Lavas or Flow-Rocks, and 2nd, 



