30 
RIO DE JANEIRO 
CHAP. 
the formation which Humboldt designates as gneiss-granite. 
Nothing can be more striking than the effect of these huge 
rounded masses of naked rock rising out of the most luxuriant 
vegetation. 
I was often interested by watching the clouds, which, rolling 
in from seaward, formed a bank just beneath the highest point 
of the Corcovado. This mountain, like most others, when thus 
partly veiled, appeared to rise to a far prouder elevation than 
its real height of 2300 feet Mr. Daniell has observed, in his 
meteorological essays, that a cloud sometimes appears fixed on 
a mountain summit, while the wind continues to blow over it. 
The same phenomenon here presented a slightly different appear¬ 
ance. In this case the cloud was clearly seen to curl over, and 
rapidly pass by the summit, and yet was neither diminished nor 
increased in size. The sun was setting, and a gentle southerly 
breeze, striking against the southern side of the rock, mingled 
its current with the colder air above ; and the vapour was thus 
condensed : but as the light wreaths of cloud passed over the 
ridge, and came within the influence of the warmer atmosphere of 
the northern sloping bank, they were immediately redissolved. 
The climate, during the months of May and June, or the 
beginning of winter, was delightful. The mean temperature, 
from observations taken at nine o’clock, both morning and 
evening, was only 7 2°. It often rained heavily, but the drying 
southerly winds soon again rendered the walks pleasant. One 
morning, in the course of six hours, 1.6 inches of rain fell. As 
this storm passed over the forests which surround the Corco¬ 
vado, the sound produced by the drops pattering on the countless 
multitude of leaves was very remarkable ; it could be heard at 
the distance of a quarter of a mile, and was like the rushing of 
a great body of water. After the hotter days, it was delicious 
to sit quietly in the garden and watch the evening pass into 
night. Nature, in these climes, chooses her vocalists from more 
humble performers than in Europe. A small frog, of the genus 
Hyla, sits on a blade of grass about an inch above the surface 
of the water, and sends forth a pleasing chirp : when several 
are together they sing in harmony on different notes. I had 
some difficulty in catching a specimen of this frog. The genus 
Hyla has its toes terminated by small suckers ; and I found 
this animal could crawl up a pane of glass, when placed abso- 
