I40 NOTES OF A BOTANIST 
Recent Geological Work on Lower Amazon 
[The preceding remarks were intended to have 
been rewritten by the author before pubHcation in 
order to incorporate the results of later geological 
research. This is shown by a pencil note written 
soon after Spruce's return to England. I have 
thought it better, however, to give the account as 
I find it, because it is very clear and precise, and 
embodies facts which I cannot find in any of the 
descriptions by the American geologists who have 
investigated the geological history of the Lower 
Amazon. My friend Professor Branner of the 
Stanford University, who has travelled all over 
Brazil as the successor of Prof. Hartt, the former 
Government geologist, referred me to papers by 
Mr. Derby and Prof Hartt in the Proceedings of 
the American Philosophical Society and in the 
Boletim do Museu Paraense for the best account 
of the geology of the Lower Amazon. These 
papers show that the valley lies in an elongate 
basin of Palaeozoic rocks in narrow belts of Silurian, 
Devonian, and Carboniferous age, the outcrops of 
these rocks forming the cataracts of the various 
tributary rivers. On the north side of the valley 
these rocks are met with at less than 50 miles from 
the river, while on the south side they are from 
100 to 150 miles distant from it; beyond them 
extends the great granitic region of Guiana and 
Brazil. In the Silurian strata at several points a 
rich molluscan fauna has been found closely agree- 
ing, often in the very species, with those of corre- 
sponding age in North America, so that their 
