MARINE BIOLOGICAL STATION AT PORT ERIN. 51 



1. The most extensive shallow-water deposit is sand. 

 In most localities along the coast of Lancashire, Cheshire, 

 and North Wales, from the sea-shore out to the 10-fathom 

 contour, the bottom is formed of more or less pure quartz 

 sand. Occasionally in spots there are local patches of 

 stones, of shells, or of mud ; but these can generally be 

 accounted for by tidal or estuarine currents, by the entrance 

 of fresh-water streams carrying down alluvium, or by the 

 presence of littoral or sub-littoral boulder clay. These 

 spots are all, however, of small area, and the great extent 

 of the bottom down to 10 fathoms is sand. 



2. Further out, however, between 10 and 20 fathoms, 

 the sand becomes greatly mixed with mud, and much 

 diversified by large tracts of shelly deposits or by patches 

 of gravel, and the fauna on the bottom also becomes much 

 more abundant. In some spots, at about 20 fathoms, it 

 is made up over considerable areas almost entirely of 

 ophiuroids (Ophiocoma nigra and Ophiothrix fragilis), 

 which fill the dredge haul after haul. At two localities 

 off the Isle of Man, viz., along the east coast from Clay 

 Head to St. Ann's Head, and off the west coast between 

 Contrary Head and Niarbyl, at depths between 10 and 20 

 fathoms, are great nullipore deposits formed of Melobesia 

 and Lithothamnion, which have a most characteristic 

 appearance, smell, and fauna. 



This area of the sea-bottom, from 10 to 20 fathoms, 

 extends across from the north of Lancashire to the Isle of 

 Man, so that opposite Barrow, for example, there is a 

 wide extent of about 50 miles in length of sea-floor at 

 depths of not more than 15 or 16 fathoms. The Isle of 

 Man is connected with England by this plateau, and is 

 separated from Ireland by deep water. 



3. Depths of over 20 fathoms are only found to the 

 west, north, and south of the Isle of Man ; and depths of 



