5 10 On flic Local and Relative Geoloyy of Singapore, [June, 



One of the most common features of the hills is the occurrence of* a 

 bed of igneous stones, — at one place large (30 to 60 cubic feet) slaggy 

 and often scoreous or amygdaloiclal, and gradually but irregularly 

 diminishing in size until they become a coarse and then a fine gravel, 

 in some places dwindling into a seam of minute grains. The beds are 

 of various thickness, — from three or more feet to a few lines, — and so, 

 often, is the same bed at different places. They may consist of a uni- 

 form aggregate of stones, or of stones mingled with loose clay, sand, &c. 

 Over this deposit there is generally a bed of soft clay, or sandy clay. 

 Sometimes more than one bed of gravel occurs. Layers of unaltered 

 angular fragments are occasionally, but rarely, found beneath these beds. 

 Layers of the small porcellanous, jaspideous, and varnished stones be- 

 fore noticed, and of large grains of quartz, are more common. All 

 these layers sometimes appear in the same section, but this seldom 

 happens. The localities where the large scoriform rocks abound are 

 often at or near the summits of hills, or where thick dykes of igneous 

 rock come to the surface, and probably in every case they mark the 

 places where the largest fissures or vents were opened. Where they are 

 most abundant they appear at the surface, and that not only in spots 

 exposed to denudating influences, but in flattish and gently sloping 

 tracts. There appears in many cases to be a connection between the 

 direction of the dykes and fissures, and that of the hills or their spurs. 

 Where good sections of the summits of dykes have been obtained 

 fragments of the rock of which they are composed, not angular but 

 scoriform, can generally be traced as a horizontal layer on the surface, 

 or disposed beneath a bed of clay, &c. to a considerable distance from the 

 head of the dyke. When the dyke is vertical these stones are accu- 

 mulated over and strewed on both sides of it. When it is inclined 

 they are spread out in the direction towards which the inclination is. 

 Two dykes adjoining each other at the surface have sometimes beds of 

 scoriae diverging from them in opposite directions, owing to their dips 

 being opposed. The above and other observable facts are all, I think, 

 explicable by the species of volcanic action which I have suggested, 

 susceptible as it is, of various modifications, without resorting to oceanic 

 agency. At all events no fact has yet come under my notice unequi- 



originated on, but lasled, or were from time to time repealed, for sometime after the 

 elevation ol the hills. 



