1880.] 49] [Crosby. 
yet I judge that no doubt can rest upon the conclusion that these 
two South American terranes must be essentially identical. But the 
Caribbean group is vastly older than the overlying fossiliferous and 
uncrystalline limestone, and hence almost certainly pre-Paleozoic. 
Therefore, besides the fact that the Brazilian rocks are largely 
crystalline, and, in consequence, presumably Eozoic, we have two 
distinct lines of evidence pointing to the same conclusion; viz., their 
almost perfect resemblance, first, to the Taconian system, and second 
to the Caribbean group; and of the Eozoic age of the last named 
formation, at least, I think there can be but little doubt. In other 
words, the facts now known justify the prediction that, if rocks 
holding Cambrian fossils are ever discovered in Brazil, they will be 
found, like the Silurian beds of that country, and like the “compact 
limestone” of Trinidad (which is probably Cambrian), to lie uncon- 
formably above the great semi-crystalline series which includes the 
quartzite, hydromica schist, and saccharoidal limestone. 
This division of my subject may be summed up as follows: — 
We recognize among the crystalline rocks of Brazil, or rather, of 
that part of South America south of the Amazonas, not less than 
four distinct and mutually exclusive series, which present a fair agree- 
ment lithologically and, so far as the evidence allows us to judge, in 
their order of succession or stratigraphically, with the Laurentian, 
Huronian, Montalban and Taconian systems. The oldest and new- 
est of these four series, or those which we may designate, provision- 
ally at least, as the Laurentian and Taconian, predominate in Brazil; 
while on the western slope of the Andes the Huronian and Montal- 
ban beds are more characteristic. 
CRYSTALLINE FORMATIONS OF GUIANA. 
Passing now north of the Amazonas to the crystalline tract of 
Guiana, we find that the geological literature is even more meagre 
here than south of the great river. The geological observations of 
Humboldt and the later descriptions of Sir Robert Schomburgk are 
too general, too little discriminating lithologically, to be of much 
value here. 
The greater part of this vast area is a wilderness into which the 
white man rarely penetrates; and, so far as I am aware, only two lim- 
ited tracts have been studied geologically in anything like a sys- 
tematic manner. These are British Guiana, and that part of Ven- 
