TIIK MAIMNK AI.O.i; OF (J I' KHNSK V 27 



('V) Currciiiii. 



A note in Xaiiirc for Sept. I, lOUi, on tlie Oeeanoo-rajjliy of the 

 Mediterranean (juoted from a Report of the ]J)a)Hsli Kx|)editioii 

 oh" H)()S~1() to the Mediterranean and adjacent seas, — deserihes a 

 "current of warm and higlily saline water which Hows eastwards . . . . 

 and tlien northwards ah)ng the dee}) depi-essions of the sea-bottom, 

 till it ai)})roach(^s tlie shores of Britain. It normally Hows to tlie 

 west of Ireland .... hut if unusually strong, it may enter the 

 shallower sea-))asins. It has been suggested that it is owing to the 

 presence of this highly saline Mediterranean water that the high 

 salinities of the English Channel and the Irish Sea are due." The 

 presence of this current would account for the appearance of many 

 southern species, whose spores have been brought thither in its How. 

 Pddina Pavi/uia, for example, is an inhabitant of the Mediterranean, 

 but is well-established as a member of the British Flora ; Litholham- 

 II ion expcoiHUin, Cordlliiia mediterranea, Nemastoma diclioiomnmy 

 (Udpomohin sinuosa are among the more i-ecent arrivals on our shores, 

 and may have travelled hither by this means: The familiar Gulf 

 Stream is also a carrier of spores and detached portions of seaweed, 

 which are able to germinate and grow in the congenial warmth of 

 the current which has brought them. 



(4) Nature of the Suh^itratinii. 



Apart from Plankton and other floating alga?, it is obvious that 

 seaweeds require an anchorage or point of attachment; mud and 

 sand are of too shifting a nature, and few species Avill be found! 

 growing on them. The abundant and varied marine flora of Guernsey 

 indicates the peculiarly suitable and varied substratum which is. 

 afforded by the structure of the Island coasts. The following quota- 

 tions, which will explain briefly the conformation of the island, are 

 taken from Anstead's Chanvel Islands and from De la Mare's; 

 paper " On the Con-elation and Relative Age of the Rocks of the 

 Channel Islands," Trans. Guernsey Soc. Nat. Hist. Sci. ii. l(S90-94: — 



" The northern part of Guernsey consists of diorite sometimes; 

 approaching hornblende rock with syenitic and granitic veins." 

 " These rocks are of a dark bluish-grey colour, remarkably fine grain,, 

 excessively hard, heavy and t(mgh " (Anstead). "The southern part 



consists chiefly of gneiss, but diorite occurs in various parts 



The diorite appears to be associated with the gneiss in the^ 



form of inclusions rather than of intrusions There is a 



considerable patch of fine-grained granite east of L'Ancresse." At 

 Cobo the granite resembles some Jersey granite described thus — 

 '* generally of a pink colour due to the orthoclase felsjjar, which i& 



abundant and contains both mica and hornblende The mica 



traps are composed chiefly of mica and felspar" (De la Mare). The 

 relative ages of these rocks De la Mare summarizes as follows : — 

 " Some of the Guernsey granites, a large proportion of the dark 

 blue diorite or diabase dykes, and perhaps some of the pink felsites 



are Areluean f pre-Cambrian). The Cobo granite, the re^ 



mainder of the diabase dykes, the quartz felsites and rhyolites 



are comprised within the limits of the Cambrian system The 



niii-a trap-dykes belong to the Carl ton it'erous period AVitli the 



