PHYSICAL FEATURES OF THE IRISH SEA. 13 



and these into smaller, and so forms deposits of dark slatey more or less angular gravel, 

 and then very coarse sand, extending for some way out from the foot of the cliff. 



The influence of the shore rocks upon the littoral fauna is an important subject 

 upon which we have accumulated some observations ; but the matter requires further 

 work and detailed discussion, and must be left over for a future occasion. 



3. Probably the great bulk of the silicious sand which forms so large a part 

 of the floor of our sea is derived proximately whatever may have been its ultimate 

 source* from the great deposits of drift which were formed in the neighbourhood 

 during the Glacial period, and large tracts of which may since have been broken up 

 by the sea. 



4. As examples of a few peculiar and specially noteworthy deposits, which are not 

 simply " terrigenous " in their origin, the following may be mentioned : 



South-east of the Calf-sound, about two miles out, at a depth of 20 fathoms, 

 there is a white shelly sand which seems to be almost wholly composed of animal 

 remains. There are broken fragments of the lamellibranchs Pecten, Anomia, Pectiinciihis, 

 Mactra, Venus, and Mytilus ; of the gastropods Cypr&a, Buccinum, Emargimda, Purpura, 

 and Trochus ; of various calcareous polyzoa, such as Cellaria fistulosa, Cellepora pnmicosa, 

 and lepralids ; of Balanus and Serpula, and of various echinoderm plates and spines, 

 and the whole shells of Echinocyamus pusillus. The deposit, when it comes up in the 

 dredge, is of a gleaming whiteness, and has a very characteristic appearance. Such 

 a deposit as this would form a rock almost wholly made up of fossils, and might 

 compare well with some Tertiary fossiliferous deposits, such as the Coralline Crag. 



A little further north, along the east coast of the Isle of Man, at about a 

 corresponding depth and distance from land, we meet with a purely vegetable deposit 

 formed of the nullipores Lithothamnion and Melobesia. On the other side of the island, 

 again, between Port Erin and the Calf, at a depth of 18 fathoms, there is a tract of 

 sea-bottom which, when brought up on deck, looks, at the first glance, like a peculiarly 

 fibrous sand, but a closer examination shows that it is entirely composed of the com- 

 minuted plates, and especially the spines, of echinids, chiefly Spatangus. We do not re- 

 member to have met with a reference to material such as this either amongst recent 

 or fossil deposits. 



There is another interesting deposit found in at least two localities on the sea-floor 

 in our district, the one between the Calf and Holyhead, and the other off King William's 

 Bank, between Ramsey and St. Bees. The deposit takes the form of irregular calcareous 

 masses (Fig. 5), cementing together the dead shells and sand grains which are lying on 

 the bottom, and making lumps like "clinkers." Hence one spot where it is found is called 

 by the Manx trawlers the " Blacksmith's Shop," the Fleetwood trawlers call it the " Smithy." 

 It is about 25 miles S.S.W. of the Calf of Man ; in ordinary clear weather the Chickens' 

 Rock Lighthouse just dipping, and the Stack at Holyhead just rising above the water, and 

 the depth is about 25 fathoms. We first heard of this interesting material from Mr. W. 

 Beck, of Douglas, and he kindly sent a specimen for us to Mr. A. Leicester, at Port Erin. 

 Mr. Leicester found the following shells in the concretion : Pecten opercularis, Cyprina 

 islandica, Venus lincta, Cardium echinatum, Nucula nucleus, Scrobicularia alba, Lucina 

 borealis, and Turritella terebra. We have obtained other specimens since. There is a fine 



* Probably to a great extent, Triassi sa dstones. 



