444 Professor J. B. Harrison—‘ Laterite’ in British Guiana. 
Surinam as (akerlogston, in French Guiana as Roche d Ravet, and is 
termed in Brazil Pedra de ferro and in Venezuela Moco de hierro. 
Samples of the various types of ironstone, of the quartz and of the 
earth with its ferruginous pisolites, which are present in it to the 
extent of 45°8 per cent. of its weight, were collected at my direction 
by the officer in charge of the station, and have been examined by 
Mr. Reid and myself in the Government Laboratory of British Guiana. 
The ultimate composition of the epidiorite at Issorora, of the red 
earth, of the pisolitic ironstone granules, and of the various types of 
the concretionary ironstone found there was determined with the 
results shown in Table III (p. 445). 
Aided by microscopical examinations of the material the mineralogical 
components of the rock and of its decomposition-products have been 
calculated as shown in the following table :— 
Taste II. 
Red Concretionary Ironstones. 
Lateritic| Iron- 
Epidiorite. | Earth. | stone 
Nos. 1 | Pisolites.| Nos. 1 | Nos. 3 | Nos. d 
and 2. and 2. | and 4. | and 6. 
Quartz . me a eres Log} 2°3 14 Oil oi “il! 
Colloid Silicw. F 
Orthoclase 5 8 119s} 
Plagioclase , 55:1 2°9 “4 1198} 6 8 
Hornblende and Pyroxene 38:0 nil 
Magnetite Se Ants 2°8 
Hematite. ee he as P}07/ 65°4 18°2 29:0 19°0 
Limonite . ahne 15°9 74:1 54:0 12°5 
Mlmvenihete ink See wee NZ 4°3 36 6 6 6 
Kaolinite Sots Say and 39°4 37 2-4 77 24°5 
gna] Crain ae lee, Ae A ya) ea 2°3 Hh 1-4 or 8 
*Bauxite . . Aen 94°2 7c 1:6 6°6 41°7 
*Minor constituents Saat ok 6 3) 3 
100-0 1001 | 100°0 | 100-0 | 100-3 | 100-0 
IDI 6 oo 6 6 | 12:0 6°6 
Gubbsitemenmne | 12°2 WL 1:6 6°6 35°1 
*Total Alumina present in 18°9 THiS? 1:0 3° 28°6 
Bauxite 
The foregoing representatives of the class of more or less ferruginous 
and aluminous deposits which in the Guianas for many years commonly 
have been termed ‘laterite’ do not possess, except in the case of the 
concretionary ITOHSLONES, the property laid down by Buchanan as — 
being characteristic of ‘laterite’—that of ‘setting’ or hardening on 
exposure to the atmosphere. Parts of them agree to some extent 
with what has been laid down as the modern scientific qualification 
