Whitaker — Oil Subaerial Denudation, 483 



segregation. A joaper, on this subject, of Mr. George Maw's, put into 

 my hands in May, 1863, gave me the first suggestion of this possi- 

 bility. 



I shall endeavour, as I have leisure, to present such facts to the 

 .readers of this Magazine as may bear on these three enquiries; and 

 have first engraved the plate given in the present number in order 

 to put clearly under their consideration the ordinary aspect of the 

 veins in the first stage of metamorphism in the Alpine cherts and 

 limestones. The three figures are portions of rolled fragments; 

 it is impossible to break good specimens from the rock itself, for it 

 always breaks through the veins, and it must be gradually ground 

 down in order to get a good surface. 



Fig. 1 is a portion of the surface of a black chertose mass ; rent 

 and filled by a fine quartzose deposit or secretion, softer than the black 

 portions and yielding to the knife: neither black nor white parts 

 effervesce with acids : it is as delicate an instance of a vein with rent 

 fibrous walls as I could find (from the superficial gravel near Geneva ) . 



Fig. 2 is from the bed of the stream descending from the Aiguille 

 de Varens to St. Martin's. It represents the usual condition of rend- 

 ing and warping in the flanks of veins caused by slow contraction, 

 the separated fragments showing their correspondence with the places 

 they have seceded from ; and it is evident that the secretion or in- 

 jection of the filling white carbonate of lime must have been con- 

 current with the slow fracture, or else the pieces, unsupported, would 

 have fallen asunder. 



Fig. 3 is from the bed of the Arve at St. Martin's, and shows this 

 condition still more delicately. The narrow black line traversing the 

 white surface, near the top, is the edge of a film of slate, once attached 

 to the dark broad vertical belt, and which has been slowly warped from 

 it as the carbonate of lime was introduced. When the whole was 

 partly consolidated, a second series of contractions has taken place; 

 filled, not now by carbonate of lime, but by compact quartz, traver- 

 sing in many fine branches the slate and calcite, nearly at right angles 

 to their course. 



I shall have more to say of the examples in this plate in con- 

 nection with others, of which engravings are in preparation. 



II. — On Subaerial Denudation, and on Cliffs and Escarpbients 

 OF THE Chalk and Lower Tertiary Beds. 



By William Whitaker, B.A. (London), F.G.S., 

 Of the Geological Survey of England. 



[PART II.] 

 4. — Chalk Escarpments. 



THE graceful outlines, smooth curves, and flowing contours of the 

 Chalk hills are well known to southern geologists ; indeed these 

 hills are the most marked feature of the south-east of England. 

 Those who hold that their form has been given by the sea, point to 



