560 Notices of Ilemoirs — Geologists' Association — ■ 



parts sliows aa characteristic white crystalline mottlings through the 

 finely crystalline greenish base. 



Adventitious minerals are developed in this and other similar dykes, 

 in nests and aggregations, such as mica, chlorite, epidote, garnets, 

 hornblende, quartz, calcite, and varieties of felspar and iron pyrites. 



At Laghtmurragha and Glencalry other dykes were described, 

 belonging to this class. Among these the hexagonal and spheroidal 

 structures are never developed, and they are scarcely ever found to 

 be vesicular or amygdaloidal. 



The second series or Post-Carboniferous dykes are probably of 

 Tertiary age, and seldom here attain a thickness of over 25 feet, and 

 generally run in straight and definite directions W.N.W. and E.S.E., 

 apparently filling vertical cracks or fissures, or along lines of faults. 

 "When occurring together, they always cut the sheet-like dykes of the 

 older series ; they are basalts with local variations, and are frequently 

 hexagonal or spheroidal in structure, often amygdaloidal and decom- 

 posing, thereby leaving the original fissures open or enlarged into 

 narrow chasms penetrating the cliffs. One of these separates Illan- 

 master from the mainland, another forms a chasm between vertical 

 walls 450 feet deep, and in part scarcely 10 feet wide, and separates 

 four small islands from their respective headlands, the view looking 

 down this cleft, with its four pairs of opposing perpendicular cliffs 

 on either side being almost unique. 



II. — Geologists' AssociATio]sr — Inatjgueal Addeess by the PsEsiDEiirT. 

 Evolution of Plant Life. 



ON November 3rd, Mr. W. Carruthers, F.E.S. (the Keeper of the 

 Botanical Department of the British Museum), gave the Pre- 

 sidential Address to the Geologists' Association, in the Library of 

 University College, his subject being a comparison of the history 

 of plant life preserved in the rocks so far as we know it, and its 

 relation to the theory of evolution. 



The origin of the existing organic forms has always been a 

 question of interest. Until a comparatively recent period little 

 diversity of opinion prevailed in regard to this matter amongst 

 students of science in Europe. The position stated by Moses in the 

 opening sentences of the Old Testament, in which all matter, organic 

 and inorganic alike, is traced to the operation of an external and 

 supernatural Creator, was universally adopted, though it was often 

 misunderstood and misinterpreted by its expounders. 



In the beginning of this century Lamarck proposed his Evolution 

 theory, according to which all organisms are derived from some few 

 simple original forms, which had come into existence by spontaneous 

 generation out of inorganic nature. Although Lamarck's theory 

 found a few supporters, it was comparatively neglected by men of 

 science until Darwin, in 1859, published his " Origin of Species by 

 Means of Natural Selection," which, at least in this country ,^ has 

 wrought an almost complete change in opinion as to the origin of 



