36 A NEW FLORA OF 



'of the writer who has investigated the subject most carefully, we 

 will name dysgeogenous and eugeogenous, names derived from 

 the comparative readiness with which they produce detritus, and 

 yield to disintegrating influences. In the North of England the 

 first is typically represented by the limestones of various ages, 

 and the other by the sandstones and shales from the Kimmeridge 

 clay down to the Old Eed. We see the two opposite types of 

 scenery contrasted better in Yorkshire than in Northumberland 

 and Durham. In the North Riding the eastern third is occupied 

 by two parallel ranges of hills, running from west to east, for a 

 length of 30 miles, from the central vale to the coast, one formed 

 from the arenaceous rocks of the lower oolite formation, and the 

 other from the calcareous upper oolite, which show the charac- 

 teristic features of the two types excellently. The flat table 

 lands of the limestone hills contrast with the irregular undula- 

 tions of the sandstone hills : the steep precipitous calcareous 

 scars, not less so with the irregular "edges" of freestone and 

 gritstone. The sandstone hills are intersected by branching 

 rivulets, which flow from their upper levels gradually down 

 their slopes into the low country. The limestone hills have 

 neither streams nor natural pools upon their surfaces, but the 

 glens slope suddenly, and the water sinks through the calcareous 

 beds to gush out in large volume when it reaches some less per- 

 meable stratum. The sandstone dales are open and irregular, 

 with gradual slopes and undulated embankments ; the limestone 

 dales are steep and narrow, with sudden slopes and enbankments 

 rising up like a wall upon each side to shut them in. In North- 

 umberland and Durhani we have only a limited and not very 

 characteristic development of limestone hill and dale. The great 

 series of beds deposited during the Mountain Limestone period, 

 so characteristically calcareous in Derbyshire and the West Hiding 

 of Yorkshire, gradually loses this character as it passes northward, 

 and as Mr. Tate has already explained, has changed completely 

 by the time that it reaches Northumberland. Unless this state 

 of things is kept in view, any one looking at our geological map 

 may easily get a very wrong idea into their mind about the phy- 

 sical geography of our field of study. "We have an instance of a 



