CHAPTER V 
A GEOLOGICAL SKETCH OF THE LOWER AMAZON, AND 
AN ACCOUNT OF SOME CURIOUS PHASES OF VEGE- 
TABLE LIFE AT SANTAREM 
I SHALL preface what I have further to say of the 
vegetation of Santarem by a brief sketch of the 
geology, and an attempt to connect the latter with 
my observations elsewhere in the Amazon valley. 
Geology, however, had no place in my programme, 
for my previous studies had not prepared me for 
working it thoroughly, and the apparently entire 
absence of fossils from the rocks of the Amazonian 
plain (for Messrs. Wallace and Bates had no more 
than myself been able to find any) took away from 
the pursuit any interest which it might otherwise 
have had for me. 
As I have already stated, the unmistakably 
volcanic character of much of the rock at Santarem 
was the most remarkable geological feature. Along 
the shore of the Tapajoz, but especially in the hills 
lying south and east from it, misshapen blocks, 
glazed and honeycombed, quite resembling the slag 
from a smelting furnace, and often of enormous 
size, were strewed about, or confusedly heaped up. 
Were these deposited on the spot, or, if not, how 
did they get there? If I recapitulate all the data 
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