22 VEGETATION OF THE PEAK DISTRICT [CH. 



Each of the succeeding chapters deals Avith a group of 

 associations, not necessarily with a formation. The associations 

 are analysed ; and, as fe,r as is possible, each association is 

 then referred to the formation to which it belongs. 



Vegetation Maps and Floristic Maps 



Vegetation maps indicate the occurrence and distribution 

 of plant communities. Floristic maps may be of two kinds : 

 they may indicate the occurrence and distribution of single 

 species or of groups of geographically related species. The 

 former maps are of the type which H. C. Watson (1832, etc.) 

 began to construct of the species indigenous to the British 

 Isles. They are very useful maps in their way, as may be seen 

 by the use to which they are put in Praeger's recent Flora of 

 the West of Ireland (1909: figs. 4, 5, 14, etc.). Such maps, 

 however, do not lend themselves to any generalized carto- 

 graphical scheme, because almost every species requires a 

 separate map to show its distribution. They bear the same 

 relation to vegetation maps that a series of cartographical 

 representations of erratic boulders would bear to a modem 

 geological drift map. Floristic maps illustrating the distribution 

 of geographically related species can hardly be said to exist as 

 regards the British Isles; but Flahault (1901) has constructed 

 such a map of France, and more recently Massart (1910) has 

 published maps of Belgium on somewhat similar lines. 



The so-called " botanical maps " illustrating numerous 

 British county and local floras are neither floristic maps nor 

 vegetation maps. The typical maps accompanying these floras 

 simply show divisions of the county into " drainage districts " 

 or other topographically convenient districts ; and no attempt 

 is made on such maps to show the occurrence and distribution 

 either of plant communities or of floristic groups of species. 



The Value of Vegetation Maps 



Vegetation maps have the same value to botanists that 

 geological maps have to geologists. Just as geologists may, 

 by consulting geological maps, know where certain geological 

 phenomena may best be studied, so botanists may, by consulting 

 vef^etation maps, know where certain ecological phenomena 



