108 ALPINE FLOWERS [PART I. 



LIMESTONES. 



Under the name of limestone must be included a very large 

 number of rocks different in texture, hardness, and general 

 aspect, but having this in common that they are chiefly com- 

 posed of carbonate of lime. The result of this composition is 

 that more than any other rocks they are liable to the solvent, 

 as distinguished from the disintegrating, action of water charged, 

 as rain- water always is to some extent, with carbonic acid. 

 This action we see displayed on a large scale in the great 

 stalactite-lined caverns in the Carboniferous limestone of the 

 North of England, or in the sand-pipes running deep into the 

 chalk of the South country. On a smaller scale, the effects of 

 this dissolving power are marked on every exposed face of 

 limestone of every age, and help to make them everywhere 

 worthy of the attention of the rock-gardener. In some 

 instances thin beds of hard limestone are weathered into a 

 curious honeycombed state, the exposed parts being of a 

 lighter colour than the inner stone ; in others the faces of the 

 beds present the appearance of a clumsy balustrade of the 

 Louis XIV. style, the interstices having been gradually eaten 

 away by the water running down the original lines of upright 

 joints. Sometimes the most peculiar forms are assumed in 

 this manner by limestones, and each kind has its own special 

 characteristic shape, to be known only by constant observation ; 

 but perhaps no rock equals the great Magnesian limestone of 

 Durham in the eccentricity or in the multiplicity of its dis- 

 guises. This limestone is of a yellowish colour, and its struc- 

 ture is wonderfully diversified, sometimes hard and compact, 

 sometimes friable, often concretionary and botryoidal, occurring 

 as a mass of radiated concentric spheres of all sizes, generally 

 crystalline, often as a distinct breccia or agglomeration of 

 angular fragments held together by a cement of similar 

 material. A walk along the coast of Durham, from South 

 Shields to Roker, will show to what vagaries of weathering and 

 denudation this extraordinary variety of conformation has given 



