992 Notes, chiefly Geological, across the Peninsula £No. 156. 



come so full that they form an impervious bed where the water collects 

 in hollows and cavities. Here it accumulates until it either trickles 

 through the passes of the side of the cliff, or finds its way out by some 

 of the nearly horizontal joints that intersect the rock. Such are the 

 sources of the shallower wells and springs observed in the substance of 

 laterite rocks. The deeper wells and springs are usually found at its basis 

 where it rests upon the impervious trap. Near the line of junction 

 the trap is almost invariably observed to be in a state of disintegration 

 either as a friable wacke, or as a brownish or greenish grey clay. The 

 laterite is no longer hard or porous ; its cavities are broken up or 

 filled with lithomarge and ochreous earth ; and in short, it presents a 

 dense bed of clay variegated with shades of purple, red, yellow, and 

 white. This clayey state of disintegration of both rocks is ascribable 

 chiefly to the collection here of the percolated water from above. 

 The line of demarcation between the two rocks is not easy to distinguish 

 as the clays are intermixed by the water ; that of the trap is easily to 

 be distinguished at a little distance from the contact by its greenish 

 hue, and soapy feel, that of the laterite is often meagre to the touch, 

 and either white, or tinged of various shades by iron. The disintegra- 

 tion of the trap rock rarely extends more than four or five feet below 

 the junction. 



The tubular cavities in the laterite have not unfrequently a hori- 

 zontal direction ; and, where numerous, impart a somewhat laminar 

 structure to the rock. They are observed to be most numerous where 

 the water, obstructed from passing lower down, is compelled to find 

 its way to the sides of the cliffs; empty sinous tubes having a general 

 vertical direction are also observed varying from a few lines to one or 

 two inches in diameter passing through the rock, one was traced 30 

 feet until it disappeared in a projecting portion of the cliff. These 

 cavities are sometimes lined with drusy crystals of quartz. The surface 

 of the interior is generally ferruginous and shining, and sometimes raam- 

 millary and stalactiform veins of manganese in the laterite. I am 

 not aware that any writer on laterite has noticed the occurrence of veins 

 of manganese associated with oxide of iron in this singular rock, a 

 mineral which has probably afforded the beautiful lilac colour seen in 

 its lithomargic earth. 



At the western base of the cliffs; about 16 miles W. by N. from 



