510 
NATURE 
{ Oct. 27, 1870 
We have nothing to do here with their failure to teach 
Natural Science, and thus to mislead where they ought to 
have led. What we now ask the people of England, and 
especially the people of London, is to put Men of Science 
on their School Boards. 
E. LANKESTER 
THE GLACIATION OF BRAZIL 
Thayer Expedition : Scientific Results of a Fourney im 
Brazil, by Louis Agassiz and his travelling Com- 
panions. Geology and Physical Geography of Brazil. 
By Ch. Fred. Hartt, Professor of Geology in Cornell 
University. With Illustrations and Maps. (Trubner 
and Co.) 
HIS thick volume of 620 pages is the result of two 
visits to Brazil, the first with the Thayer Expedition, 
the second during a vacation holiday of “ some months.” 
The author has proposed to combine with his own personal 
observations all the information on this subject obtainable 
from other sources, and thus give a complete view of the 
present state of our knowledge of the geology and physical 
geography of this vast and interesting region. The design 
is an admirable one, but the execution of it is, in some 
respects, disappointing. 
The first great fault of the book is, that it has been 
swelled by the introduction of much irrelevant matter. 
Mr. Hartt’s own journeys were mainly along the coast, 
from Rio Janeiro to the Amazon, with occasional trips of 
a hundred miles or so into the interior, and he inflicts upon 
us pages of unimportant detail on the topography of small 
rivers, crecks, and harbours, which have no bearing on the 
geology or physical geography of the country. Detailed 
descriptions of the marine animals and fossils collected 
would also have been better in an appendix than in the 
body of the work where they are given. The arrangement 
of the book, too, is faulty, since it treats of the provinces 
of Brazil in succession, and makes no attempt to indicate 
the great physical divisions of the country, and there 
is not a single geological or physical map of Brazil, or of 
any part of it; the maps alluded toin the title-page 
being mere outline or sketch maps of small districts, 
or plans of harbours and mouths of rivers. Another 
strange defect is the absence of all measurement of 
heights. The author travelled without barometer or 
aneroid ; he, consequently, everywhere roughly estimates 
his heights, and gives no sections, but a few “ideal” 
ones. Notwithstanding the bulk of this volume, it does 
not complete the geology of the voyage, for we are in- 
formed that Mr. St. John, another geologist attached to 
the expedition, who travelled more in the interior of 
the country, will give the results of his observations in a 
separate work. 
But although we have thus plainly indicated the defects 
of the book, there is much valuable matter to be found in 
it. The author has been very diligent in examining all the 
chief authorities on Brazil, and has extracted from them 
most of their geological matter ; and among the extracts 
from Spix and Martius, Prince NeuWied, Darwin, Gardner, 
Halfield, and others, are to be found many interesting 
passages descriptive of the peculiarities of the scenery 
and geology of the country. The chapters on the coral 
reefs of the Abrolhos and on the gold mines of Brazil, 
the account of the exploration of the bone-caves by 
Lund, and the appendix on the Botocudos Indians, will 
furnish some interesting matter for the general reader, 
while the student of science will obtain (though with some 
difficulty) a notion of the general physical and geological 
characteristics of an almost unexplored region. 
The most striking geological feature of tropical South 
America east of the Andes is the enormous extension of 
gneissic rocks, which appear to form the whole founda- — 
tion and much of the surface of the country, from the 
cataracts of the Orinooko to Paraguay and the southern 
frontier of Brazil. 
Brazil and Guiana, as well as the low plain which sepa- 
rates the watersheds of the Orinooko and Amazon, are 
of this rock, which is considered to be of Laurentian age. 
Its characteristic features are the great dome-like masses 
and the conical peaks or pillars, generally of more or 
less smooth and rounded outlines, a peculiarity dependent 
All the great mountain tracts of 
on the decomposition of all exposed surfaces, which fall — 
away in concentric flakes. Great hemispherical domes 
up to athousand feet in diameter are one of the results 
of this decomposition wherever a more resisting mass has 
occurred. Still more extraordinary are the vertical pil- 
lars of rock, that rise up at intervals out of the forest to 
some hundreds, or, in the case of the Pedra lisa, in the — 
province of Rio de Janeiro, to more than three thousand 
feet high. Similarly formed peaks or pillars in Fernando, 
Noronha, and St. Helena have been formed by injections 
of fluid felspathic lava. What an enormous amount of 
denudation do these isolated pillars indicate! 
In South Brazil a few tracts of Silurian and Carboni- 
ferous rocks occur, but the next formation of any extent 
is the Cretaceous, which consists of sandstones, generally 
upheaved and fractured. Other sandstones, which cover 
an immense extent of country, and form the ranges of flat- 
topped hills from one to nearly three thousand feet high, 
called ¢adolezros, are in perfectly horizontal strata, and as 
these lie unconformably on the cretaceous rocks they are 
presumed to be tertiary, although no fossils have yet been 
found in them. 
We now come to a very wide-spread, yet recent and 
superficial deposit, which is at once the most puzzling and ~ 
the most interesting feature in Brazilian geology. Thisis — 
a layer of clay or loam, varying in thickness from a few 
feet to one hundred, and wrapping in its folds hill and 
valley, over vast tracts of country, including the steep 
slopes and summits of some of the highest mountains. 
All Rio de Janeiro, and all the coast provinces visited by — 
our author, were thus covered. 
It has been described in — 
Minaes Geraes and San Paulo, and Prof. Agassiz has — 
observed it in all the northern provinces as far as the 
Amazon valley. 
tertiary formations. This clay is of a red colour, and is 
It covers alike the gneiss and the 
evidently formed of the materials of the adjacent and ~ 
under-lying rocks, but ground up and thoroughly mixed. 
There is never the least sign of stratification throughout 
its mass, although it very frequently rests on a thin layer 
of quartz pebbles. It contains, scattered through it, 
rounded and angular boulders of quartz, gneiss, and other — 
rocks, and the surfaces upon which it rests are always 
more or less smooth and rounded. Our author always 
speaks of this formation as “ drift,’ and he agrees with 
