494 Professor J. B. Harrison—‘ Laterite’ in British Guiana. 
a concretionary mass, but that it is made up of exceedingly fine 
felspathic rock powder, a few particles of which show the 
characteristics of plagioclase, with varying proportions of kaolinite, 
bauxite, and oxide of iron. Although it cannot be described as 
‘laterite’ when judged on the lines laid down by Mr. Crook, its 
properties closely resemble the characteristic ones ascribed to that 
substance by Buchanan, and on account of which he proposed for it 
the name ‘laterite’. 
Oolitic ‘ Laterite’.—Du Bois, in his monograph on the laterites 
of Surinam, showed as figs. 2, 3, and 6 of pl. i two varieties of 
the components of Surinam laterite which he termed respectively 
‘« pisolithischen Kisenerzkonkretionem”’ and ‘‘ oolithartigen Beauxit”’. 
I have obtained specimens closely resembling in general appearance 
these types—a red ferruginous one from near Arawak Matope on the 
Cuyuni River and a white one from the Berbice River. The specimen 
from the Cuyuni River consists of spheroids filled with dark-red ochre 
surrounded and cemented together by a white cementing material 
having a concretionary structure. It is an aggregate of ironstone 
pisolites cemented into a mass. That from the Berbice River consists 
of white and yellowish-white and of a few reddish spheroids cemented 
together by a white material in a similar manner to the Cuyuni 
specimen. When first obtained the specimens were quite soft, and 
could be very easily cut with a knife, the spheroids being the harder 
parts of them. The cementing material has gradually hardened, and 
now the rocks are somewhat harder than are any of the specimens of 
purely ferruginous or aluminous concretionary laterite I have described 
in this paper. The cementing material is now the hardest part of the 
specimens, the innermost part of the spheroids the softest. From 
their very marked properties of induration on exposure to the atmo- 
sphere these rocks appear to have a well-founded claim to the term 
‘laterite’ as used by Buchanan. But they are not laterite in the 
sense of being mainly aluminous in composition, the restriction which 
has recently been superimposed on Buchanan’s original description 
of laterite. This is clearly shown by the chemical and proximate 
mineralogical compositions detailed in the following analyses :— 
Taste XVII. 
Matope, Cuyuni Berbice 
(red). (white). 
Quartz s : : : : “06 6°79 
Colloid Silica : : : : *40 33 
Combined Silica . : : ; 24°07 36°92 
Aluminium Oxide . P ; : 21-42 34°82 
Tron Peroxide 5 : : ; 40-80 3°85 
Magnesium Oxide . ; : : “85 16 
Calcium Oxide : : : ; SIL 7/ ‘07 
Sodium Oxide E : : : nil nil 
Potassium Oxide . ; : m 20 32 
Water . 5 d : F : Tbe 12°74 
Titanium Oxide . ' } : *95- 3°85 
Phosphoric Anhydride . : : trace trace 
Manganese Oxide . c ‘ : nil nil 
100°33 99°85 
