LIFE IN RIO CONTINUED. 87 
a good photograph. This locality afforded me at once an 
opportunity of contrasting the decomposed rocks which 
form a characteristic feature of the whole country (as far 
as I have yet seen it) with the superincumbent drift, and 
of making myself familiar with the peculiarities of both 
deposits ; so that I trust I shall be able hereafter to dis- 
tinguish both, whether they are in contact with one another 
or found separately. These decomposed rocks are quite a 
new feature to me in the structure of the country. Imagine 
granite, gneiss, mica slate, clay slate, and in fact all the 
various kinds of rocks usually found in old metarnorphic 
formations, reduced to the condition of a soft paste, ex- 
hibiting all the mineralogical elements of the rocks, as 
they may have been before they were decomposed, but 
now completely disintegrated and resting side by side, as 
if they had been accumulated artificially in the manner 
you have seen glass cylinders filled with variously colored 
sands or clays to imitate the appearance of the beds of 
Gay-Head. And through this loose mass there run, here 
and there, larger or smaller dikes of quartz-rock or of 
granite or other rocks equally disintegrated ; but they 
retain the arrangement of their materials, showing them 
to be disintegrated dikes in large disintegrated masses of 
rock ; the whole passing unmistakably to rocks of the 
same kind in which the decomposition or disintegration 
is only partial, or no trace of it visible, and the whole 
mass exhibiting then the appearance of an ordinary meta- 
morphic set of rocks. 
" That such masses forming everywhere the surface of the 
country should be a great obstacle to the study of the 
erratic phenomena is at once plain, and I do not therefore 
wonder that those who seem familiar with the country 
