6*70 On the Local and Relative Geology of Singapore, [July, 



a few of the better marked disguises which the rocks assume under this 

 potent influence. I say disguises, because the geology of the Malay 

 Peninsula almost wholly resolves itself into the identification of the 

 original rock under its multiplex transformations. Without a key to this, 

 derived from a minute examination and comparison of the modes of 

 alteration, the whole is a dark riddle, or our geology becomes a conge- 

 ries of bewildered gropings and sheer mistakes. 



The first or lowest degree of alteration, let us say in a clay, is the 

 formation of isolated blotches of a reddish colour in the rock, but 

 unaccompanied by any other apparent change. 



2d. A slight comparative hardness in the blotches. 

 3rd. In addition a grittiness, — they may now be termed nodules 

 or concretions, and we may include in this catalogue all degrees from 

 an incipient grittiness to a hard compact character, which gives the 

 nodule the appearance of an imbedded pebble ; [the nodules are some- 

 times hard and compact without being gritty or quartzose, and they 

 are gritty in their nascent state where the rock is originally arenaceous 

 in any degree.] 



4th. The nodules bulge out at different points, and the preceding 

 three degrees may be repeated in nodules of this shape. 



5th. The arms or branches unite so that the rock is pervaded by a 

 complete congeries or ramification of red, rounded, but irregularly 

 shaped, branches. The form of these branches varies very much, but 

 is generally uniform for a considerable space. Very frequently it is as 

 if ginger roots were continued in all directions. At other times the 

 spaces between the ramifications are narrow sinuous perforations or 

 isolated vesicles or deep straight tubes or chambers in tubes. This struc- 

 ture is sometimes the result of an allied or predisposing structure in 

 the rock affected, and at other times, it appears to be wholly superin- 

 duced by the altering agency. In this last form the red portion is 

 found of various degrees of hardness, but not so soft as the first 

 degree. In general it possesses a medium degree of hardness so as to 

 be cut with an axe.* 



6th. In this class we may include the products all degrees of heat 

 that has been suddenly applied in sufficient force to produce calcina- 

 tion, and this distinguishes it from all the preceding, in which the 

 * It hardens on free exposure to the atmosphere and is used in building*. 



