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VI. 



THE MAEITIME AND MAEINE LICHENS OF HOWTH. 

 By matilda G. KNOWLES. 



[communicated by K. LLOYD PRAEGER.] 



(Plates III-IX, and Map.) 



[Read June 24. Published August 16, 1913.] 

 TABLE OF CONTENTS. 



PAGE 



Formations and Associations — con- 

 tinued. 



(4) Verrucaritt maura Belt, 107 

 (a) Belt of Marine Verru- 



I. Introduction — Eocks, Coast-line, 



Tides, WindSj Climate, Mois- 

 ture, Previous Work, Area in- 

 vestigated, Assistance, 



II. Formations and Associations — 



1. Lichens of the Rocky coast, 

 i. Silicious Rocks, 



(1) Ramalina Belt, 



(2) Orange Belt, 



(3) Lichina Vegetation, 



I. Introduction. 



HowTH Head forms the northern boundary of Dublin Bay. It stands well 

 out into the Irish Sea, an isolated area of high rocky laud of about 4 square 

 miles in extent, the highest point being about 560 feet above sea-level. A 

 low isthmus of sand and gravel scarcely half a mile wide, and lying about 

 10 feet above ordinary high-water mark, connects it with the mainland. 

 This isthmus is part of the raised beach that extends along the County 

 Dublin coast from Olontarf northwards. 



The Rocks (5) are entirely of the Palaeozoic series, being mainly Cambrian 

 grits, shales, and quartzites, much contorted and interspersed here and there 

 with bands of pure white quartz and numerous dykes of igneous rock, many 

 of which may be seen on the sea-cliffs, and on the shore at low tide. Beds of 

 Carboniferous limestone, resting unconformably on the Cambrian series, lie 

 along the western side of the promontory, stretching from Sutton to Howth 

 Harbour and Balscadden Bay, where they are exposed on the shore. 



The Coast- line is about 8 miles in circumference, and faces all points of 



SCIENT. PROC. K.D.S., VOL. XIV., NO. VI. N 



