138 NOTES OF A BOTANIST 
up, and upon which several small tributary streams 
of the Rio Negro take their rise. I have ascended 
nearly to the head of two of these, the Igarape da 
Cachoeira and the river Taruma, both of which run 
in the upper part of their course over a white sand- 
stone, usually so soft that it crumbles under the 
foot, but with interposed layers of marble-like rock, 
which cause those streams to descend in a succession 
of falls, a few miles apart, each fall being over a slab 
or sheet of this harder rock. I have visited three 
falls of the Igarape da Cachoeira having this 
character, the lowest of them being no more than 
12 feet high, while the first fall of the Taruma (the 
finest cataract in the Amazonian plain) is over 30 
feet, and the slab of white stone from which it 
leaps projects so far that one may walk on a ledge 
a few yards lower down without getting a drop of 
water from the fall. This structure quite corre- 
sponds to what I observed at Santarem, and 
Wallace at Monte Alegre. Moreover, on the 
Rio Negro, as on the Amazon and Tapajoz, the 
white sandstone reposes on the gritty sandstone of 
Para. 
Several of the hills below Monte Alegre, namely, 
those of Parauaquara and Paru (see Plate in Bates's 
Naturalist on the River Amazons, chap, vi.), are 
table-topped, but some of those covered with forest 
appeared to be round-backed. I hardly doubt, 
however, that all are of the same formation, and 
that they vary only in the material being of a more 
or less yielding nature ; for there are a few bare 
flat summits which I suppose to have a similar 
hard coping to that of the table -mountains of 
Santarem. 
