Yol. 68.] FEOM THE AECTIC BED IN THE LEA VALLEY. 2S3 



reaches through a stony channel, with probably frequent stretches 

 of sandy margins ; then spreading out into a pool or series of pools 

 or marshes, or at least flowing at a much gentler gradient. I do 

 not mean to imply that the paludal species are actually in situ : they 

 are much too fragmentary for this to be the case ; but their 

 dominance, on the whole, seems to imply that the present position 

 is, at any rate, much nearer to their original station than to that 

 of the rupestral and terrestrial species. 



The second conclusion to be drawn from the material is as to the 

 nature of the climatal conditions. The association is certainly an 

 Arctic one. Quite a considerable number of species (namely, Tortula 

 aciphylla, Timmia norvegica, Hypnum fastiglatum, H. moUe^ 

 H. turgescens) are Alpine-Arctic mosses which are either entirely 

 extinct in Britain at the present day, or are now conlined to one 

 or two summits of the higher Scottish mountains ; wliile, with the 

 possible exception of OrtJiotrichum diaplianum (the determination of 

 which is perhaps open to question), all the remaining species are 

 such as might occur under climatal conditions similar (though not 

 identical topographically) to those which would be suitable to these 

 others. 1 have gathered the great majority of the species within a 

 limited area in Tornean Lapland (lat. 68° N.), at little above the 

 sea-level ; and the conditions necessary to produce these associations 

 at Ponder's End might, I think, be very fairly compared with 

 those of the Arctic mainland of Europe at the present day. 



The Upper Bed exhibits some slightly different features, notably 

 in the absence of all the terrestrial and rupestral forms. The 

 association is entirely a paludal one, but I have found nothing 

 which does not occur in one or other of the beds, with the single 

 unimportant exception of Amhlystegium JUicinum var. vallis-clauscef 

 that is, the form with excurrent nerve. On the other hand, there 

 are no species included which indicate a colder climate than that of 

 the present day, unless Hypnum capilJifolium be considered to do so; 

 while the presence of H. aduncum (Groui^ pseudqfluitans) might, if 

 anything, point the other way, but neither of these could adequately 

 serve as a basis for any definite conclusion. With regard to the 

 Upper Bed, therefore, so far as the moss-remains point, there is 

 clearly a slight difference of origin as compared with the other beds ; 

 but there is no evidence to show whether there was any long 

 interval of time separating it from the others, or any material 

 difference in the climatic conditions obtaining at the epoch of its 

 deposition. 



Facts worthy of notice are the total absence of any trace of 

 Sphagnum, or peat -moss, and the very sparse occurrence of 

 Camptothecium niiens, a species which generally occurs with some 

 frequency in prehistoric paludal moss-associations in this country. 

 Whatever may be the cause, however, the point is one rather of 

 botanical, than of geological, or of general interest. 



