1903. Coi.:^. — Recent Irish Geology, 9 



little covevS, that lovers of igneous rocks will find this remote 

 and picturesque region as fascinating as it is to the strati- 

 grapher. 



DYNAMIC AI^TERATION OF A I^KINSTKR ANDKSITK- 



Mr. H. J. Sejmiour {^Sci. Proc. Royal Dublin Society, vol. ix. 

 1902, p. 568) has provided a delightful study of the changes 

 set up in an igneous rock by pressure and accompanying 

 molecular re-arrangement. At Deerpark Hill, near Donard, 

 Co. Wicklow, dykes of andesite, of lyambay porphyr}^ type, 

 occur in Silurian strata, and are traversed by a tongue of the 

 lycinster granite. Contact-metamorphism has consequently 

 affected them ; but the granite has sheltered them from the 

 pressures which continued to accompany the uplift of the 

 lycinster Chain. Farther north, however, at Ballymooney, the 

 same series of dykes has borne the full brunt of the pressure, 

 and the two types of metamorphism can be conveniently com- 

 pared. The felspars, under pressure, have become arranged 

 in parallel planes, and have become elongated and leaf-like. 

 Secondary biotite has arisen, and its cr3'Stals have increased 

 in size as the molecular movements went on in the mass. The 

 felspars show strain-shadows under the microscope in the 

 earlier stages of change ; but in the more extreme examples 

 each flake passes into a granular mosaic free from strain- 

 shadows, the process of elongation nov; being carried on by 

 solution and recrystallisation (p. 572). Van Hise is cited for 

 similar observations in America. 



The beautiful photographs furnished from actual hand- 

 specimens give an admirable idea of the phenomena described. 

 We may note that Mr. Seymour, unlike some of his 

 colleagues, regards the dykes as of Bala age, on the evidence 

 furnished by I^ambay and Portrane. 



COAST-EROSION. 



Prof. J. P. O'Reilly {Proc. Royal Irish Academy ^ vol, xxiv., 

 section B, 1902, pp. 95-202), discusses the dcvsirability of record- 

 ing, by systematic survey, the changes due to erosion or sub- 

 mergence of the Irish coast-line. About one hundred pages 

 of the paper consist of quotations from various authors, many 



A3 



