70 baker's north YORKSHIRE. 



The rich bryological flora of North Yorkshire has its head 

 quarters amongst the well irrigated porous-rocked eugeogenous 

 hills and slopes.* To these nearly all the characteristically Mon- 

 tane species are restricted and amongst them most of the common 

 mosses attain their greatest abundance and luxuriance. A few- 

 species, notably Neckera crispa, Tortula tortuosa, and Tricho- 

 stomum fiexicaide are common everywhere amongst the rocks 

 of the dysgeogenous hills and almost entirely absent from the 

 eugeogenous tracts. And what has been said of the mosses will 

 apply with precision to the Lichens : a good list of species for 

 North Yorkshire as a whole, the more northern species confined 

 to, and the commonest species attaining their greatest abundance 

 and luxuriance amongst the eugeogenous hills, a few species 

 almost invariably associated with the calcareous rocks and almost 

 confined to them. 



The Precipices and Watej'falls. — The unequal waste of different 

 kinds of rock is also worthy of attention in its bearing upon two 

 conspicuous features of scenery. First, the precipices. Along 

 a great part of the coast line, the cliffs have a compact arenaceous 

 cap over a more or less considerable thickness of mainly argil- 

 laceous groundwork. In Whitstonchff and the other scars of 

 the Middle Oolite a mass of compact limestone rests upon a 

 base of Oxford Clay, and we have seen how in the west, clays 

 are interpolated between every band of the Mountain Limestone. 

 The lower part of these cliffs wastes away faster than the upper. 

 At first the upper part overhangs, becoming all the time gradually 

 loosened by rains and frosts, till at last it becomes overbalanced 

 and falls with a tremendous crash, strewing the hill-side or beach 

 with its broken blocks. Lastly, the waterfalls. Here again the 

 softer rocks are wasted away and those composed of less porous 



* Though Teesdale is coloured as subdysgeogenous in the Map it can scarcely be con- 

 sidered as such without great exception and what is said above does not apply to it. In 

 fact strata of both lithological types are in Teesdale so much mingled together that it 

 presents the characteristics of both the types combined. It has the heatherland and swamps, 

 the irrigated cliffs and gills, the rich bryology and lichenology of the eugeogenous hills and 

 furnishes also upon the limestone and basalt many of the characteristically Xerophilous 

 species. 



