go baker's north YORKSHIRE. 



and offer the greatest resistance to abrading influences, we shall 

 have to place in the first rank the compact Limestones, Granites 

 and Basalts ; after them the compact Slaty rocks and Limestones 

 like the Coralline Oolite and Calcareous Gritstone ; then must 

 follow some of the metamorphosed igneous rocks and the harder 

 kinds of compact sandstone like the Brimham Grit and Kello- 

 ways band; then many of the Freestones, Flagstones and 

 Chalks ; and last of all and most absorbent of all are most of the 

 rocks in which the argillaceous element is predominant, the 

 Plates and Clays of the Carboniferous beds, the Shales and 

 Clays of the Trias and the Lias, the Oxford Clays and Kimmer- 

 idge Clays of the Oolite. As regards permeability when bedded 

 in extensive strata it is almost always the Limestones which are 

 the most conspicuously traversed by fissures and breaks, and the 

 softer argillaceous rocks which are the most compact, the sand- 

 stones and harder siliceo-aluminous beds occupying an inter- 

 mediate position. The power which the different kinds of rock 

 have of yielding detritus depends upon their position in the 

 scale which has been indicated, and, especially when they form 

 hill-masses and are permeable upon a grand scale, the soils which 

 cover the dysgeogenous rocks are comparatively dry, whilst those 

 which cover the eugeogenous rocks are comparatively humid. - 

 We see that difference in respect of the characteristics which 

 have just been noticed does not by any means run precisely 

 parallel with difference in chemical composition. Calcareous 

 rocks are not always dysgeogenous nor arenaceous and argilla- 

 ceous rocks always eugeogenous, though such is most frequently 

 the case. We must put the Limestones of the Carboniferous, 

 Permian and Oolitic periods upon one side and place Basalt 

 along with them ; and on the other side Clays like those of the 

 Lias and Triassic System, and Sandstones like those of the 

 Trias, the Millstone Grit and the Lower Oolite, Chalk with the 

 Slates and most of the Granitic rocks occupying an intermediate 

 position. And a characteristic feature of our field of study and 

 that which constitutes its special interest from the point of view 



