30 Outlines of Geology, 



larly well marked, and hence the cause of those land slips as they 

 have been called, one of which took place to a great extent in 

 1799, and another about ten years ago. 



The clays, gray chalk, and marles, which are common in many 

 parts of the country that bound the chalk hills, scarcely admit of 

 distinction into strata ; they are often more or less intimately 

 mixed with green sand and contain beds, masses, and nodules of 

 sandstone and limestone ; these all appertain to the formation we 

 are now speaking of, and lie upon those very extensive beds of 

 sand, commonly called ferruginous or iron sand, of the characters 

 and situation of which it will now be right to treat more 

 at large. 



This stratum must be distinguished from the sand lying above 

 chalk, as that of Blackheath and of Bagshot. It is much more 

 extensive, and constitutes a leading feature of many of those 

 countries which contain or border upon chalk hills. It is 

 accompanied and often blended with some varieties of lime- 

 stone, and frequently it scarcely is to be regarded as a distinct 

 formation from green sand — perhaps its best character, its most 

 marked and leading feature, is the quantity of oxide of iron that 

 it occasionally contains, and which is so considerable in ^ome 

 parts of Kent and Sussex, as to have been formerly employed as a 

 productive ore of iron. These ferruginous masses and veins are 

 very abundant in and about Crowborough Heath, and the extensive 

 district comprehended in a triangle, of which Dover, Beachy Head, 

 and Alton, form the points, is chiefly composed of this kind of 

 sandstone — here and there intermingled with other beds, but 

 seen in characteristic masses on the coast near Hastings. Leith 

 Hill, in Surrey, is also a good specimen of this formation ; it rises 

 to nearly 1000 feet above the level of the sea: at Bottom 

 Head on the coast of Yorkshire, it forms an elevation of nearly 

 1800 feet, which is perhaps the greatest height which it attains in 

 England. This sandstone is seen with most of its peculiarities in 

 the neighbourhood of Tunbridge Wells, and although in many 

 places it is almost barren, or only covered with furze and heath, in 

 others, where it contains embedded or intermixed clay and lime- 



