﻿230 Proceedings of the Royal Physical Society. 



Zone 2, extending 30 feet down from the lower limit of 

 Zone 1, and characterised by the great abundance of 

 Ascopyhllum nodosum; Zone 3, extending downwards 

 auother 26 feet, with the characteristic weeds Fucus 

 vesiculosus and Fucus serratus ; and Zone 4, which included 

 as much of the generally recognised " Laminarian Zone " as 

 was exposed at ordinary low tides. In addition a Drift 

 Zone was recognised, extending from the lower limit of 

 the grass to the upper limit of Zone 1. 



Description of the Zones. — The drift, consisting of masses 

 of Fucus vesiculosus, Fucus serratus^ Ascophyllum, Zostera, 

 Polysiphonia, etc., extended 15 feet downwards. 



Zone 1 extended 24 feet downwards, upper limit 49|^ feet 

 wide, lower limit 54^ feet wide, this limit being marked by 

 a transverse ridge of rock in the centre. 



The stones in the upper 16 feet of this zone ("Zone 1, 

 Upper ") were almost bare of weed, the lower limit of this 

 weedless area being a line between two rocks, which we 

 called the Pelvetia Eocks. 



In the lower 8 feet of this zone ("Zone 1, Lower -'), the 

 stones were mostly covered with Pelvetia canalicidata and 

 Fucus platycarpus. The depth of water at ordinary high 

 tide was 2 J feet at the lower limit of Zone 1. 



Zone 2 was marked at its low^er limit by two conspicuous 

 rocks covered with Ascophyllum nodosum. The distance 

 between these was 96 feet, and the extent downwards of the 

 zone was 30 feet. The stones here were not so flat as in 

 Zone 1, and scattered boulders of larger size were present 2 

 or 3 feet in longer diameter. The depth of water at ordinary 

 high tide was 6| feet at the lower limit of Zone 2. 



Zone 2 was characterised by Ascophyllum nodosum, which 

 showed a marked boundary at the upper limit, but extended, in 

 scattered tufts, to a considerable distance below the lower limit. 



For convenience of collecting we divided this zone into 

 upper and lower halves, each 15 feet in downward extent. 



Zone 3 extended down 26 feet to the commencement of 

 the Laminaria. 



Fucus serratus was here dominant, especially in the lower 

 half of the zone. 



