Professor J. B. Harrison—‘ Laterite’ in British Guiana. 489 
considered by him to be of Lower Bagshot age, I regard as Pleistocene 
drift, such as may be met with in many places, not only in the Isle of 
Purbeck, but in the New Forest and the Isle of Wight. At the Rabbit 
Warren at Headon Hill there is nearly or quite 100 feet of sand and 
flint gravel, the flints being in every respect exactly similar to those 
from Creechbarrow. One of the workmen picked up, at a depth of 
about 13 feet, in one of the pits a piece of Bembridge Limestone 
associated with the flints in the gravel, which is quite conclusive 
evidence that the gravel cannot be of Bagshot age. 
In conclusion, T should like to thank Mr, A. H. Bloomfield for 
valuable assistance, and to assure any persons visiting the Isle of 
Purbeck for the purpose of studying its stratigraphy or collecting 
fossils that they would do well to secure his services. 
HXPLANATION OF PLATE XXXIV. 
Fossils from the Bembridge Limestone of Creechbarrow Hill, Purbeck, in the 
Sedgwick ah Cambridge, collected by H. Keeping. 
Fics. 1, se omus [ Bulimus] ellipticus (Sowb.). 1, with shell preserved ; 
2, internal cast. 
Egg of Amphidromus (?). 
Cyclotus cinctus, Edwards; x 13. 
Felix ocelusa, Edwards. 
Glandina |_Achatina| costellata (SowD.). 
Clausilia striatula, Edwards. 7, natural external cast, x 14. 8, wax 
impression of external cast, x 13. 
CO > Orie O° 
Iil.—Tue Resrpvat Earrus or BrivisH GuiaNaA COMMONLY TERMED 
‘ LATERITE ’. 
By Professor J. B. Harrison, C.M.G., M. As F.G.S., F.1.C., assisted by 
K. D. Rep, Assistant Analy st British Guiana. 
N pages 20-2 and 99-105 of the Geology of the Gold Ields of 
British Guiana I gave a condensed account of the residual earths 
derived from the gradual decomposition of igneous rocks in situ which 
characterize wide areas in British Guiana as well as in the neigh- 
bouring countries of Venezuela, Dutch Guiana, French Guiana, and 
Brazilian Guiana. This deposit forms in many places a widespread 
very thick blanket-like coating to the igneous rocks from which it is 
derived, and owing in many “places to its striking resemblance in 
general properties to the typical Indian formation described by 
Buchanan in 1807 it has been alluded to by many authors and by 
numerous mining engineers as ‘laterite’. I gave on p. 101 two 
analyses of lateritie deposits which I selected from many I had made 
as showing the general composition of the earths. Unfortunately 
I omitted to show in them separately, as I had done in the original 
analyses, the proportions of silica present as quartz and of that present 
in a combined state. If I had done this it would have been seen that 
the earths contained but little combined silica and a relatively high 
proportion of alumina presumably present in the state of hydrate. 
For instance, in the Tumatumari sample which I collected myself from 
a deep cutting in the laterite lying on the diabase of the Tumatumari 
cataracts a few feet only above the surface of the unaltered rock, out 
of 51°76 per cent. of silica 49°35 is in the form of quartz, leaving 
2°41 per cent. in the combined state in the presence of 24°55 per cent. 
