Feb.. 1894. VOLCANIC DYKES. 113 



margin of tlie littoral, these dykes, piercing at their shore-end deep 

 into the land, form natural passes on to the beach. Used from time 

 immemorial, they now form the slip-ways or slips found in every 

 parish in the island, and upon which the various parish assemblies 

 have spent really considerable sums in improvement. I have 

 examined a great number, and fully 75 per cent, of these slips mark 

 the presence of an intrusive dyke running outwards to the sea. 



Why these should be barren of life is easy of explanation. 

 Their trend exposes them directly to the full fury of in-shore 

 gales, which alternately with off-shore winds play a continual see-saw 

 of removing and bringing back the surface layers of sand and shingle 

 along the course of the dyke. Stability of environment, so necessary 

 to the slow-spreading forms of littoral life, is wholly wanting. 



In other cases, these dykes serve as determinants in the formation 

 of many of the prettiest of the innumerable bays that line the coast. 

 The great majority of such are small; sometimes independent inlets, 

 but more generally secondary indents that go to make up the larger 

 bays. In each the dyke originally formed a point of weakness, 

 whereon the waves constantly pounding, first tore out a narrow path- 

 way the width of the dyke-filling, and then, when the waves worked 

 with greater force confined between the walls of this channel; the 

 breach was gradually widened by the undermining and wrenching out 

 of blocks of the mother rock. Given the initial weakness of the kind 

 provided by such a dyke, it is difficult to set limits to the destroying, 

 bay-making force of the waves acting continuously during a long 

 lapse of time. 



That this necessary time-factor has been present in Jersey, I am well 

 convinced from many personal observations. At several points 

 along the shore and high above the present sea-level I have traced 

 unmistakable raised beaches composed principally of beds of loose, 

 well-rounded pebbles (L'Etacq and along the North coast). I can 

 also testify to high-lymg sands and gravels, in some cases to be seen 

 even resting upon the old beach pebbles. These sands, I feel certain, 

 were deposited during a time of slow subsidence, and represent, I 

 suggest and believe, the ancient soil and sub-soil torn from the land 

 surface as the sea gradually gained upon the land by contemporaneous 

 sinking. Apparently such deposits synchronise with the high-level 

 (so-called glacial) drifts of Britain. Hence the bay-sculpture of Jersey 

 took place chiefly during pre-Glacial times when the land was at a 

 much lower level than at present, and was continued through a 

 portion of the Glacial period when the island was slowly sinking still 

 further. When upheaval came — as I believe it did— towards the 

 close of that time, throwing the land much above its present level, 

 and when a land-connection was brought about with France, the 

 waves ceased to play havoc with the coast-line, retiring well to the 

 eastward of the island. The beginning of this continental period was 

 marked by the sojourn of Palaeolithic man in Jersey, as evidenced by 



I 



