Ixxxviii 
MAXGANESE DEPOSITS OF INDIA. 
psilomelane, or pyrolusite — irregularly mixed with iron-ores. But this 
rock does not always consist entirely of iron and manganese-ores. It 
often contains patches of quartz, quartzite, slate, or phyllite. Under 
the microscope it is seen that these are residual pieces of rock set in a 
matrix of ore, and that the latter has been formed by the metasomatic 
replacement of. the former. Examination of the masses of rock in the 
field, especially as revealed in the workings for manganese, confirms 
this deduction, and shows that there is a downward passage from the 
lateritic mass of iron and manganese-ore at the surface, through rock 
containing more and more quartzite, slate, or other rock, and less and 
less ore, to a rock free from all signs of ore. As the rocks that have 
undergone this conversion into ores by metasomatic replacement do 
not usually contain more than a very small proportion of manganese, 
it is e\adent that the manganese must have been brought in from 
outside by percolating waters. On account of the Hmited extent of 
each of these masses of rock, their different elevations, their want of 
horizontal bases, and the numerous cases in which the rock contains 
angidar fragments of other rocks, most geologists would probably 
prefer to consider these occurrences as distinct from the masses of 
typical laterite occurring in horizontal sheets, often of considerable 
extension, and free from included fragments of rock different in 
character from the laterite. For this reason these occurrences are 
referred to in this Memoir as lateritoid, to indicate their similarity to 
laterite, and yet introduce a distinction. It is evident that my 
views as to the origin of these masses of lateritoid and their included 
manganese-ores are practically identical with Maclaren's theory of the 
origin of laterite in general. The high-level laterite of Talevadi on which 
Maclaren bases his theory undoubtedly is related to the lateritoid 
occurrences, and may be considered as the connecting link between 
lateritoid and true high-level laterite. 
The term lateritic is taken to include both true laterite, high-level 
and low-level, and lateritoid, and the following classification is given 
of the lateritic manganese-ores :— 
Classification of the deposits of lateritic manganese-ores. 
I. — In low -level 'aterite : — 
1. Goa. 
2. Chengalput. 
