SUPPLEMENT TO BOTANICAL REPORT — -1878. 45 



Instances of introduction by human agency are not common 

 among the cryptogamia, but the following appears to be one: — 

 On the gritstone coping of an old clough or sluice on the River 

 Don at Dykemarsh near Thorne, below high water mark, several 

 mosses occur which have not been found elsewhere in that neigh- 

 borhood, a low-lying alluvial district, and of these three at least, 

 viz. : — Racomitrium laimginosuin^ Ptychomitritun polyphylhim and 

 Tortilla refiexa are decidedly of a mountain type, and may have 

 been introduced with the stone — millstone grit — from the high 

 western moors of Yorkshire. 



A line in which the observations of members of the Union 

 may be usefully directed is the relation of the flora to the geological 

 and chemical character of the soil. The following is suggested as 

 a classification of soils for botanical purposes : — ■ 



1. Tgneo-metamorphic — granite, basalt, clay slate. 



2. Calcareous — limestone, marl, chalk. 



3. Argillaceous — clay, shale. 



4. Arenaceous — sand, gravel, sandstone, grit. 



5. Peaty. 



with intermediate varieties. 



The following is merely an outline of the botanical charac- 

 teristics of these several soils, the details being left to be filled in 

 and the whole confirmed or refuted by future observations. 



I. Igneo-metamorphic. — The representatives of this group 

 in Yorkshire are few, viz. : — the whinstone of Teesdale and the 

 Silurian slate of Craven and the borders of Westmoreland. The 

 phaenogamic flora on these rocks is characterized not so much by 

 certain species being constantly or commonly present where they 

 occur and absent where they do not, as by the general richness of 

 the flora which they bear, which frequently comprises many local 

 or rare species, and often exhibits in company plants partial to 

 hard "dysgeogenous" rocky soils, some choosing limestone and 



