GEOLOGY AYE MINERALOGY. 63 
layers of lava, besides eleven of volcanic mud ■ wliile at Horse 
Pasture, on the same coast section, seventy layers of the former and 
six of the latter, are plainly distinguishable. 
These layers or strata vary considerably in composition and very 
greatly in thickness, so that their examination next claims our atten- 
tion. The volcanic mud or laterite beds arc in colour generally of a 
yellowish brown passing into red, and where the non-intervention of 
rubble happens their bright red edges show plainly the effect pro- 
duced by immediate contact with the burning hot lava. They vary 
from eight or nine inches to several feet in thickness, and, where the 
mud has fallen into irregular hollows or bowls in the surface of the 
lava, they attain a greater thickness, exhibiting also quite a sedi- 
mentary form of deposit. In many places this mud is to be seen 
burnt as hard as a brick, while in others it is little harder than 
cheese ; some extremely thick massive beds of it exist at the Red 
Quarry, Eock Cottage, &c., passing into the form of a vitrified 
scoriaceous kind of slag, in which state it is a good deal used for 
building purposes ; being easily dressed for faced work, many of the 
principal buildings in Jamestown are constructed of it; when 
protected by a thin coating of plaster or cement it is found to be 
durable enough for such uses. Traces of small roots of plants occur 
in some of these beds of laterite. I have noticed them especially near 
Pierie’s Revenge, but they are probably recent, and no fossiliferous 
remains are found in them beyond embedded fragments of volcanic 
rock, scoriae, and pumice, similar to those which make up the beds 
°f rubble. Some of these mud or ochre beds, as they are called, 
exhibit the most brilliant red, yellow, and purple tints, which at 
first sight are suggestive of fitness for colouring pigments ; but no 
Use being made of them in this respect, their real value seems to 
exist in forming indicatory records of subsequent disturbance, or 
otherwise, in the general strata. 
The rubble or agglomerate beds of small fragments of stones, 
as bes, and cinders, which generally immediately overlie the mud 
strata, range from two to three feet in thickness ; the stones of which 
t,le y are made up are about two or three inches in size, in appear- 
ance much worn and slightly rounded, and somewhat adhering 
together. The face of the hill between Jamestown and Ladder Hill 
affords a good opportunity for inspecting these rubble beds. Gfene- 
la % the lava has flowed over them without disturbing them much, 
