Glare Island Survey — Marine Algae. 16 9 



(3) Tides and Currents. — The presence of a good ebb and flow on Clare 

 Island gives a wide intertidal region for shore-collecting. At Westport 

 Quay the rise and fall during spring- tides is about 15 feet, and in April 

 and September 16 feet 6 inches, whilst with neap-tides there is a rise of 

 12-13 feet. On Clare Island the range is, if anything, greater. Low water 

 at spring-tides is in the middle of the day. In certain spots (i.e. between 

 the islands in Clew Bay and at Darby's Point, Achill Sound) there is a strong 

 current, and the vegetation is of a different character from that found in other 

 parts. Ballacragher Bay, owing to its narrow opening, has but a small 

 tide — not more than 5-6 feet — except during springs. 



2. Physical Nature of the Coast and Conditions of Exposure. 



Our district presents great diversities in the physical nature of the shore ; 

 and in describing the same it will be both convenient and natural to divide 

 it into two areas, viz. (1) Clare Island, and (2) the mainland. Speaking 

 generally, the island presents an exposed rocky coast, whilst the mainland 

 consists of sheltered ground. In view of the possibility of future work in 

 the neighbourhood, a detailed account of the coast-line is given. 



(1) Clare Island, — With the exception of the bay near the harbour and 

 a few sandy patches elsewhere, the whole shore is rocky and cliff-bound. 

 Taking the different parts of the island in order, we find that on the south 

 side the rocks are composed of Silurian slate, which forms flat slopes where 

 the beds lie more or less horizontally, but which is very sharp and rugged 

 where the strata are upturned. Eock-pools, narrow gulleys, and deep 

 channels are frequent, and these were found to be useful, as this part of 

 the shore is as a whole somewhat rough and exposed for general collecting. 



The eastern end of the south shore, and from the corner of the bay 

 to Kinnacorra, is composed of Carboniferous sandstone, a formation found to 

 afford excellent collecting-ground. Various degrees of slope and exposure 

 are presented ; and towards Kinnacorra there is a fine series of flat rocks 

 and a number of shallow pools. The Carboniferous sandstone is continued 

 to Portlea, a semi-sheltered bay on the north-east side of the island. A 

 boulder-beach surmounts the upper part of this bay; and the rocks below 

 are flat, with a vegetation somewhat different from that found elsewhere. 

 Further north, towards the lighthouse, the slate is again in evidence; and 

 here caves and vertical surfaces, receiving little direct sunlight, are found, 

 and several shade-loving species appear in the open. Though bounded by 

 cliff's, the shore- at this point is easily accessible. The fine stretch of cliff 

 on the north-west side of the island is for the most part precipitous, and 

 the narrow strip of shore below is very exposed and difficult of exploration. 



E.I.A. PBOC,, VOL, xxxr, B 10 



