8 INTRODUCTION. 



found in such situations. Yet I think the LICHENS 

 to be surer indications of igneous rocks. Lecanora 

 glaucoma, L. ventosa, L. coccinea and tartar ea, Parme- 

 lia omphalodes, P. Fahlunensis, P. stygia, and P. 

 aquila, are good indicators of eruptive masses ; and so 

 also are Gyrophora proboscidea, G. erosa, and G. 

 cylindrica. The curious tinder-like Blistered Umbili- 

 caria (Z7. pustulata), is almost peculiar to granitic 

 rocks. 



On steep hills and downs, where thyme delights to 

 spread its aromatic odour upon the breeze, and the 

 turf is kept down by the nibbling of the sheep, the 

 grasses, clovers, and other plants become excessively 

 minute, as may be witnessed on the chalk pastures of 

 the Isle of Wight, or the sides of the beauteous 

 Malvern hills. This circumstance is thus alluded to 

 by DYEB, in his poem of The Fleece, in intimating 

 the best and most favourite sheep walks. 



" On spacious airy downs, and gentle hills, 



With grass and thyme o'erspread, and clover wild, 



The fairest flocks rejoice ! 



* they crowding round, with silence soft 



The close wov'n carpet graze ; where nature blends 



Floio'rets and herbage of minutest size, 



Innoxious luxury." 



The same author also pleasingly mentions some of 

 the plants that distinguish chalk soils, and adverts 

 to the wide airy downs, then all unenclosed, and 

 whitened over with numerous flocks. Similar excur- 

 sive views, though with other objects in view, are 

 taken by the botanical explorator. 



" All arid soils, with sand, or chalky flint, 

 Or shells diluvial mingled; and the turf 

 That mantles over rocks of brittle stone, 



