140 Proceedings of the Royal Irish Academy. 



of the whole associations were made in a number of widely-separated 

 places, so that a good idea was obtained of the composition and variants 

 of each association. Thus, these letters grew to represent known 

 associations ; and while in characteristic ground a single letter, such 

 as P, or G, or C, entered on the map, supplied all the needful informa- 

 tion, in ground where there was an overlap or intermixture of associa- 

 tions, the facts were expressed by a combination of letters, arranged 

 in order of abundance of the species which they represented. Thus 

 CGP expressed a Callunetum with a good deal of Ulex G(dlii and its 

 dependent species, and less of Pteris Aquilina and its usual associates. 

 Ap signified a pasture into which Ulex eurojjceus and Pteris Aqiiilina^ 

 in equal quantities, have made considerable incursions. 



In mapping on mountain land, where man's operations have not 

 disturbed the surface by ploughing, or the water-supply by drainage, 

 the changes of vegetation are usually much more gradual than in the 

 lower grounds; and the absence of fences and landmarks sometimes 

 makes mapping difficult. 



Here we found that a distant view often shows distinctly, by 

 a difference of colour, the boundary between different types of vegeta- 

 tion wliich could be mapped ; the ground in question being afterwards 

 closely examined to find the nature of the change of vegetation 

 indicated by the difference of colour. It is in the autumn that these 

 colour-differences are most marked ; then the rich red-brown of 

 the Eracken, the golden-brown of Scirjnis cmspitosus, the dark red 

 of the Cotton-grass, contrast with the deep purple-brown of the 

 Callima', the golden-yellow of the blossoming Ulex Gallii picks 

 it out at a long distance from the dark, flowerless masses of 

 U. europcBus ; and the grey of the dying rushes is clearly distinguish- 

 able from the green of the grass-associations. It only remains to be 

 added, that we almost invariably worked together, the one checking 

 the other's decisions as to the position of boundary lines, and analysis 

 of the vegetation. While in many cases the boundary lines between 

 different associations are absolutely sharp (such as the edges of colonies 

 of Pteris and Jimcus), those in which the predominating species are 

 social rather than gregarious often shade one into another by almost 

 imperceptible degrees. Thus, on many of the broader mountain slopes, 

 pure C {Calluna), dry and bushy, by degrees gives way to CS 

 {Calluna + Scirpus), a low, mossy vegetation, which passes again 

 into SC {Scirpus + Calluna), shorter, wetter, without frondose mosses, 

 but with Sphagnum, and constituting the characteristic association of 

 the higher grounds ; and this occasionally passes into that rare type of 



