as 



of the so-called Malm or Firestone Rock, -ft5~ 



escai-pment. Locally it is known under the name of Malm, appa- 

 rently an old Anglo-Saxon word signifying a soft sand or building 

 stone; ox Jirestone, because of its employment for furnaces, and 

 its capacity of not being aflfected by heat ; or hearthstone, because 

 of its use for giving a white appearance to hearths and flagstones. 



Near Merstham and Godstone the rock has been largely 

 quarried for building and other purposes, and good sections of it 

 are exposed. Seen from a short distance it might readily be 

 mistaken for chalk, as it is of a white or greyish white tint. 

 When newly quarried, it has a light brown appearance, which 

 gradually gives place to white in the process of drying. The 

 rock is soft and earthy when moist, but becomes considerably 

 harder by drying on exposure. When thoroughly dry it is 

 relatively light, owing to a minutely porous structure, and from 

 the same cause it is largely absorbent of water. 



In some places the whity-brown rock gradually passes into 

 rock which is considerably harder, and of a bluish tint ; and in 

 places these bluish portions become irregularly nodular in form, 

 and are disposed horizontally in distinct beds, like the flints in 

 chalk, and thus add to the illusory resemblance between the 

 Malm and Chalk. These blue nodules are locally termed ' ' flints ' ' ; 

 but they are quite distinct in appearance from genuine chalk- 

 flints, and, unlike these latter, they are not clearly delimited 

 from the white matrix in which they are enclosed. 



When tested by dilute sulphuric or nitric acid, the nature of 

 the Malm is at once seen to be different from that of genuine 

 Chalk. In some cases no action whatever results, thus showing 

 the absence of carbonate of lime, of which real chalk is nearly 

 entirely composed ; in other instances a slight ebullition takes 

 place, indicating the presence of a small proportion of lime. 



Examining a freshly fractured smi'ace of the rock, first by 

 means of a good hand-lens, we can readily discover the presence 

 of silvery-white scales of mica, powdery granules of milky-white 

 silica, and minute threads or rods of a greenish or translucent 

 appearance. In places also the rock seems filled with minute 

 empty tubes of capillary dimensions. Wheia a thin transj^arent 

 section of the harder and more compact portions of the rock is 

 viewed under the microscope, it is seen mainly to consist of 

 numerous minute straight or curved rods with definite walls, and 

 with a central axial portion usually of a different tint to the 

 exterior. These rods are in close contact with each other, but 

 not otherwise attached than by the cementing matrix of the 

 rock; and there is no regularity in their disposition, so that in 

 the section some are cut through nearly in the direction of their 

 length, whilst others are cut obliquely, and others directly trans- 

 verse ; these latter apj^earing as two concentric circles, an outer 

 light and an inner of a dark appearance. 



