LITHOLOGY. 



51 



which we are now occupying is that in it the strata of the 

 different periods not only underlie well-defined districts, but that 

 they are composed either of rocks of well-marked eugeogenous 

 type or of well-marked dysgeogenous type, or of bands of the 

 two kinds mixed up together in the deposits of one period : and 

 that, as we have already seen, rocks of intermediate lithological 

 constitution, as occupying large tracts of surface, are entirely 

 absent. 



Their Distribution throughout North Yorkshire. — The following 

 table, then, is a repetition, except that the thickness of the beds 

 is omitted, of that which was given at the end of the chapter on 

 Geology, each series being referred to its proper lithological type. 



LITHOLOGICAL CLASSIFICATION OF THE YORKSHIRE STRATA. 



GEOLOGY. 



Approximate area 

 in square miles. 



Lithological character. 



Mountain Limestone and Basalt 

 Millstone Grit 



330 



330 

 10 

 500 

 660 

 200 



So 



Subdysgeogenous 



Eugeogenous 



Dysgeogenous 



Eugeogenous 



Eugeogenous 



Dysgeogenous 



Eugeogenous 



Magnesian Limestone 



Trias 



Lias and Lower Oolite 



Middle Oolite 







So that we have on the west bands of hard dry rock with thick 

 eugeogenous interpolations between them forming the edges of 

 most of the dales and ascending in some places to the loftier 

 mountain summits, but more usually these summits and the 

 higher surfaces of the moorlands, like their slope in the direc- 

 tion of the central valley, are formed of eugeogenous materials. 

 Next follows a narrow strip of dysgeogenous and a broad area 

 of eugeogenous lowland country, and on the east are two ex- 

 tensive tracts of moorland with contrasting lithological char- 

 acters, both of which rise into the Middle Zone, and last of all 

 we have on the south of them a eugeogenous valley, the pro- 

 portion of eugeogenous surface to that of dysgeogenous being 

 for North Yorkshire as a whole fully three to one. 



April 1S8S. 



