INTBODUCTION. 5 



carboniferous strata. The Lichens of the genera 

 Collema and ITrceolaria, and Lecidea immersa and 

 rupestris, are in general very partial to calcareous 

 rocks, especially about old quarries ; and Collema 

 nigrum delights to occupy the -surface of exposed 

 oolite. The Extinguisher-Moss (JEnealypta strepto- 

 carpa and vulgaris), also well points out calcareous 

 strata. 



The Chalk has been celebrated in Britain for the 

 beautiful Orcliidice it nourishes, as 0. militaris, O. 

 ustulata, and the singular Man, Monkey, Drone, and 

 Spider orchises, scarcely met with except on chalky 

 soil ; hence several beautiful localities, as Box Hill, in 

 Surrey, are celebrated for and resorted to by botanists 

 for such rarities, and thus local botany, from the 

 peculiarities affected by plants, merits particular at- 

 tention. Some other rare plants, as Anemone Pulsa- 

 tilla, Seseli Libanotis, Pliyteuma orbiculare, Cineraria 

 campestris, and BarkJiausia foetida, particularly affect 

 chalky pastures, so that to some extent the plants of 

 a district will be limited by mineralogical considera- 

 tions. Yet the boundary line may not be very strictly 

 observed, and where a neighbouring formation is in 

 many respects similar, there the same plants will be 

 found on geological strata of very different ages. 

 Thus Anemone Pulsatilla grows on the oolite of the 

 Cotswold hills as well as on the chalky downs of 

 Cambridge and Herts ; so also Cineraria campestris is 

 met with on the oolite hills near Cheltenham ; while 

 Carex digitata, a peculiar rock plant, nourishes on the 

 woody precipices that decorate the banks of the Wye, 

 nor is less at home on the fallen oolitic blocks that 

 strew the Cotswoldiau woods with ruinous debris. 



