THE MANX SAND-DUNE FLORA 171 



they may always be seen in profusion. Not a single species was 

 noticed on this occasion, and only one or two on a previous visit, 

 some years ago, in September. 



(6) The rapid transition from the sand-dune vegetation to 

 that of heathland, with the presence of Pteris, Callitna, Erica, and 

 Ulex, all of which are either excessively rare or absent from the 

 Lancashire dunes, is especially noteworthy. 



The causes which bring about these differences are apparently 

 twofold. The dominant factor is probably the great depth of the 

 subsoil water, due perhaps to the sand overlying pebble beds 

 derived from the boulder clay. We were informed that at Point 

 of Ayre it was possible to dig a depth of some seventeen feet 

 without reaching water. At Southport, on the contrary, it lies 

 only a few inches beneath the surface of the deeper hollows, and 

 often stands in pools. Another factor, which probably strongly 

 affects the vegetation, is the apparently smaller lime content of 

 the soil. Shells are less plentiful in the sand, most of which is 

 probably derived from the boulder clay of the north of the island. 

 The bulk of sand is also smaller than that delivered to the 

 estuarine dunes of the mainland. Owing to this deficiency of 

 material, or to the steeper inclination of the land, the dunes are 

 less extensive and of slower growth, and appear to go through a 

 constant alternation of growth and demolition. The high boulder 

 clay banks in the vicinity prevent the spread of blown sand to 

 any considerable distance inland, and the material is not supplied 

 in sufficient quantity to enable the dunes to make any marked 

 advance on the seaward margin. Here in several places there is 

 abundant evidence of recent erosion. 



The poverty of species will be evident on perusal of the 

 following list, which, whilst doubtless very incomplete, probably 

 includes the majority of the plants found at the several points 

 visited. The List of Plants of the Isle of Man, published by the 

 Kev. S. A. Kermode, does not help much, as localities are rarely 

 quoted, but some of those he enumerated may possibly have been 

 from this area. If so, they are certainly not obtrusively evident. 

 Amongst those he names which are likely to occur are Glaucium 

 luteum, Crambe maritivia, Trifolium striatum, T. arvcnse, Anthyllis 

 vuliieraria, Carlina vulgaris, Leontodon hirtus, Erythrcza Cen- 

 taurium, Etqjhorbia Paralias, E. portlandica, and Sedum acre. 

 Most of these are abundant on the drier Lancashire dunes, and 

 there seems to be no adequate reason for their absence here, if 

 they really are absent. 



About Jurby and Lhane several well-marked zones of vege- 

 tation could be discerned. 



I. The Strand Association. — This in some places is developed 

 on shingle, in others on sand. It forms an almost continuous 

 band dominated by Atriplex, amongst which we were able to 

 distinguish (although not yet flowering) A. hastata Ij., A. Bahing- 

 tonii Woods, and A. laciniata L. Other plants observed were 

 Cakile maritima Scop., Glaux maritivia L., Arenaria i^eploides L., 

 and Salsola Kali L. On pebbles where the ground was shingly 



