556 Professor J. B. Harrison—‘ Laterite’ in British Guiana. 
The following changes are indicated as having occurred during the 
degradation of the granite and the hornblende-granites at Mazaruni 
and Mahdia :— 
Taste XXII. 
! 
| Mazaruni. Mahdia. 
: ; Hornblende : 
| Granite. | Pipe-clay. Granite: Pipe-clay. 
| | 
Silicamne haste ae 73°81 49°61 68°20 29°04 
Aluminium Oxide. . | UC | || 14°47 15°83 11°30 
Iron Peroxide . . . | PATS) WSS K oket9 3°43 1-21 
Magnesium Oxide. . | 72 07 2°14 18 
Calcium Oxide. . . *88 | nil 3°49 04 
Sodium Oxide. . . | 2°80 -28 3:07 nil 
Potassium Oxide . . | 4:81 | “36 2°88 18 
IWiateia: viieray tts talons “74. | 6°22 “50 3°15 
Titanium Oxide . . 62 ! "62 46 *46 
| 
| 
G07 2 yl aeengecke 100 45°56 
Allowing for the added water in each and for slight apparent 
increases in the alumina and iron oxide of the Mazaruni specimen, 
there is a loss of 33 per cent. of the constituents in the case of the 
granite and of 54°5 per cent. in the case of the hornblende granitite. 
The losses in each 100 parts of the various constituents work out 
as follows :— 
Taste XXIII. 
Mazaruni. Mahdia. 
Silica 3 ‘ : : 32°8 57°4 
Alumina .. : A ; nil 28-4 
Tron Oxide. ; : nil 64:7 
Magnesium Oxide ; : 90°3 91°6 
Calcium Oxide . e : 100 98°8 
Sodium Oxide . i A 90 100 
Potassium Oxide . ‘ 92°5 97°2 
In the cases of the conversion of the rock into pipe-clay there are 
apparent losses of silica present as quartz as compared with the 
amount calculated to be present in the granite and the hornblende- 
granitite. ‘This is due to re-arrangement of the material by washing, 
which has separated the finer particles from the coarser ones, which, 
as a rule, form coarse sands to fine angular gravel on the surface 
of the pipe-clay. 
In the foregoing description of the British Guiana lateritic earths 
and their components, I have confined myself to the laterites which 
are in situ, and have not described the so-called low-level laterite or 
the ‘‘Alluviale Laterit or Sekundare Laterit’’ of G. C. Du Bois, 
which he defines as ‘‘ Aluminous Laterit” or as the ‘“‘ Alluvium yon 
Lateritdetritus ’’. Where I have seen alluvial deposits of this nature 
in British Guiana they have been mixed to such an extent with the 
detritus from granitic rocks or even from clastic rocks that they have 
