t23 NATURAL HISTORY MISCELLANY. 
These Devonian rocks, lying quite horizontally, reach close up to 
the base of the Serra do Ereré, and run along it for some distance. 
The Serra is composed of heavy beds of coarse sandstone, with a 
slight admixture of feldspathic clay, and so exceedingly compact 
that a fracture passes through the grains of sand. This is the gen- 
eral character of the rock; some is not so compact, and there are 
one or two comparatively thin beds of hardened feldspathic clay. 
The rock is without fossils. 'The whole series dips towards the 
southeast approximately, the angle being in some cases as high as 
15°-20.° I studied this locality for a month, and I came away 
with the only conclusion that seemed legitimate, viz.: that the 
-Serra was older than the Devonian rocks of the plain to the north. 
It is not a table-topped Serra, and does not belong to the same 
system as the table-topped hills of Almeirim, Paratiquéra and 
Santarem, which I believe to be Tertiary. The group of hills of 
Ereré and Paittina, is entirely different from anything else I have 
seen on the Amazonas, and it seems quite unique. 
I did not find the geological structure of the Amazonian 
valley as simple as I expected. Along the line of the main 
river it is very monotonous. So it is along the lower Mississippi, 
but the valley is bordered by older rocks, Eozoic, Silurian?, De- 
vonian and Carboniferous. Nor are the clays, etc., so uniform in 
their distribution as I expected to find them. I have seen clays 
from the Devonian, Carboniferous and Tertiary so exactly alike 
that it would be impossible to distinguish them, in the hand speci- 
men, from the recent clays. 
I am preparing a report on my geological studies on the Ama- 
zonas, which I shall publish as soon as possible. — Cm. FRED. 
Hartt, Jan. 17th, 1871. 
Oricix or Dramonps. — Professor Morris has started a new 
theory as to the source whence diamonds are derived. Hitherto 
they have been looked upon as coming from igneous and meta- 
morphic rocks, like garnets, rubies, and many other precious 
stones; a better knowledge of the geology of the diamond dis- 
trict of South Africa, leads us to conclude that these stones ooa 
from certain stratified beds containing, besides reptilian remains, 
numerous plants and much fossil wood. These beds are known 
as the “ Karoo” or Dicynodon beds. Professor Morris calls to 
mind the remarkable fact (well known to botanists and mineralo- 
ny AE Sas Gea a 
