Chap. XX.] 
MANGANESE IN FAULT-ROCK. 
405 
rocks of Bijawar age, but also rocks of Vindhyan age, in which case they 
also contain fragments of Vindhyan sandstone. The age of these dykes 
must therefore be post- Vindhyan ; and Mr. E. Vredenburg, who has made 
a careful study of these breccia dykes, is inclined to regard them as of 
Gondwana age and as having been formed at the time of great tectonic 
disturbance by which the Gondwana basins were faulted. In many 
cases the matrix of these dykes has been replaced by black manganese 
oxide, the result being a rock composed of the angular fragments of 
the breccia, usually quartz, set in a black matrix of manganese 
oxide. The time at which this replacement of the matrix of the breccia 
by manganese oxide took place is, of course, not known ; but if the time 
of the formation of the breccias be really the end of the Gondwana 
period, then this replacement is probably post-Gondwana and pre- 
Lameta. I will not give here an account of particular occurrences. 
These will be found under the headings of the respective areas. 
C. A. Hacket has found veins of manganese oxide in iault-rock near 
Manganese-ore in Datunda in Bundi State. The age of this fault- 
fault-rock. Bundi State, rock is, of course, not known. But if it belong to 
the great boundary fault separating the Aravallis and Upper Vindhyans 
in this part of India, then it is post-Vindhyan in age. 
