TRANSACTIONS OF THE SECTIONS. 75 
extend for about sixty miles round the city of Bahia, and on the new road to the 
Chapada by the Mato, or forest of Orobo. 
The conclusions which may be arrived at from these and other sources are, 
generally, that— 
1. There is a uniform strike and dip throughout the province within these 
limits, say, N.N.E. and 8.8. W., with comparatively little variation. 
2. The province may be geologically divided into zones. 
(1) Conglomerate and schists near the coast. 
(2) Sandstone in the Reconcayo from the city to the Lago of the river Para- 
guassu. 
(3) Of primitive rock extending to the pastoral district of the Serra da Man- 
gabeira. 
(4) Of sandstone in that serra. 
(5) Of primitive rock with nearly level surface (Taboleiros). This is some twenty 
leagues in breadth, and is the district of cataracts on the rivers. It is traversed 
by enormous masses of quartzose rock. 
(6.) Of forests under which probably sandstones predominate. 
(7) Of limestone. 
(8) Of conglomerates forming the Chapada, so called from the horizontal line 
which the tops of the hills present to the eye. All these cross the province from 
the Rio Paraguassu to the Rio di Sao Francisco. 
The Chapada is 200 miles from the west side of the Bay of All Saints, commonly 
known as Bahia, z.e. the bay which is again twenty-seven miles from the city of 
that name. It forms the eastern watershed of the Rio di Sao Francisco, and has 
within itself the sources of the rivers which fall into the sea within the circuit of the 
great river. Its height above the level of the sea may be approximately stated as 
3000 feet. The diamond workings are carried to the top. The conglomerates of 
the Chapada differ from those of the coast principally in that the former are, and 
the latter are not, highly metamorphic; they have also greater development in the 
Chapada, as schistose formations, have on the coast; both contain diamonds, but 
those near the coast have been discovered but recently, and for local reasons the 
workings, though rich, have been abandoned. 
The geological series at the Chapada is, descending— 
1. Conglomerate ; 3. Sandstone; 5. Schist; 
2. Quartzite ; 4, Limestone; 6, Primitive rock. 
These are traversed by dykes and veins of trap and chert, and intervening between 
the harder rocks, veins of dirt are not uncommon, as also of sand and clay-slate. 
These afford facilities for the entrance of water between the strata, by which their 
rapid disruption is effected ; and caverns, named Grunais, are often formed by the 
disintegration of the softer rocks beneath the conglomerate. 
While at the Chapada (December 1865) the author ascertained that the quartzite 
is the matrix of those crystals of iron pyrites the presence of which marks the dia- 
mond cascalho or gravel, but saw no trace of diamonds in that rock; and since the 
abound in the Grunais, of which the conglomerate forms the roof, concluded that 
diamonds are formed in the softer veins and strata which separate the harder rocks. 
When diamonds are found, cascalho (a water-worn gravel) is present. The most 
marked constituents of this are :— 
1. Crystals of pyrites. 6. Pingua Wagoa (rolled hyaline 
2. Specula of magnetic iron, quartz). 
3. Fejoes (schorl). 7. Pedra de ferro (oxide of iron). 
4, Fabras, ze. brown hydrophos- | 8. Pedra de fogo (black silica). 
5. Cabocles{ phate of alumina. 
The mineral equivalents are taken from M. Damon’s analysis, from which it appears 
that the presence of Yttria characterizes the cascalho of the Chapada. 
Diamonds are found of all colours, but the colour is mostly superficial. Green 
predominates, but each locality has its characteristic colour, quality, and crysta!- 
lization, which are well known. 
