a 
Oct. 27, 1870] 
NATURE 
511 
Prof. Agassiz that its peculiarities are such as unmistake- 
ably to indicate its glacial origin. 
This is truly a startling conclusion, and one which has 
hitherto been received in this country with some in- 
credulity. Prof. Agassiz was thought to be glacier-mad ; 
but if we separate his theories from his facts, and if we 
carefully consider the additional facts and arguments 
_adduced by Mr. Hartt in this volume, we shall be bound 
to conclude that, however startling, the theory of the 
glaciation of Brazil is supported by amass of evidence 
which no unprejudiced man of science will ignore merely 
because it runs counter to all his preconceived opinions. 
Mr. Hartt’s facts and deductions have the more weight, 
because he is evidently not very enthusiastic on the sub- 
ject, and because he fairly states the sources of error in 
observation, and fully discusses such other modes of 
explaining the facts as have been proposed. He acknow- 
ledges that in some cases the decomposed gneiss cannot 
be distinguished from the “ drift ;” but he shows that in 
the former the materials remain 7 sifu, especially the 
quartz veins, while in the latter all are mixed and ground 
up together; and wherever the two are seen in contact for 
any distance, the sudden cutting off of the quartz veins at 
the drift, and other well-marked characters, render it im- 
possible to confound them. He also adduces several 
other phenomena which are strongly indicative of a glacial 
origin. Both inthe Orang Mountains and in Bahia there 
are valleys with no outlet, and in Alagoas there are many 
deep lakes in rock-basins. In the province of Bahia there 
are extensive bare, elevated, rocky plains thickly strewn 
with angular blocks of stone, some of which are erratics, 
and evactly resembling the drift-covered plains of the north. 
On similar elevated plains, far removed from any higher 
land, Mr. J. A. Allen (another member of the Thayer 
£xpedition) found numerous deep and smooth pot-holes 
worn in solid gneiss. They were of various sizes, the 
largest seen being elliptical, eighteen feet long by ten 
wide, and twenty-seven feet deep. Similar pot-holes are 
known to be formed by glacial waterfalls, and they are 
found over the glaciated regions of New Brunswick and 
Nova Scotia. Heaps of débris, exactly resembling glacial 
moraines, have also been found both in the south and 
north of Brazil. Mr. Hartt is satisfied of their resemblance 
to true moraines in the valley of Tijuca near Rio, and 
Prof. Agassiz has described others still more perfect in 
Ceara, only four or five degrees south of the equator. 
After describing these in detail, he concludes: “I may 
say that in the whole valley of Hasli there are no accumu- 
lations of morainic materials more characteristic than those 
I have found here, not even about the Kirchet ; neither 
are there any remains of the kind more striking about 
the valleys of Mount Desert in Maine, where the glacial 
phenomena are so remarkable ; nor in the valleys of Loch 
Fine, Loch Awe, and Loch Long, in Scotland, where 
the traces of ancient glaciers are so distinct.” It can 
hardly be maintained that the discoverer of glacial pheno- 
mena in our own country, and who has since lived in such 
a pre-eminently glaciated district as the Northern United 
States, is not a competent observer; and if the whole 
series of phenomena here alluded to have been produced 
without the aid of ice, we must lose all confidence in the 
method of reasoning from similar effects to similar causes 
which is the very foundation of modern geology. The 
7 
only objection of any weight that has been made to this 
interpretation of the phenomena, is the fact of the absence 
of glacial striz ; but Mr. Hartt states that no strie or 
polished surfaces have yet been found even in the extreme 
south of the continent where the glacial phenomena are 
undisputed. It is at best a negative argument, and as 
such cannot neutralise those of a positive nature. We 
must also remember that we have no indication of the 
age of the Brazilian or southern glacial epoch. It may 
have occurred much earlier than that of the northern 
hemisphere, and the greater lapse of time, combined with 
the powerful decomposing and denuding agency of tropical 
rains, may have obliterated most of such marks. 
The physical difficulty of the conception of tropical 
glaciers may be resolved into the question of whether a 
subsidence to the extent of ten ar twelve thousand feet 
may not have subsequently occurred ; since a greatly in- 
creased elevation at a time when a severe glacial epoch 
reigned in the south temperature zone, would probably 
lead to the glaciation of the southern tropics down to 
what is now the sea-level. ; 
A much more serious objection seems to be the biologi- 
cal one. If the whole surface of what is now Brazil was 
recently covered with a sheet of ice, whence has arisen the 
wonderfully rich and varied, and, in many respects, peculiar 
flora and fauna that now inhabit it? Judging from the 
map of the Atlantic given in Maury’s “ Physical Geography 
of the Sea,” a rise of twelve thousand feet would only add 
a belt of about four hundred miles in width to tropical 
America ; but a great part of this might have enjoyed a 
truly tropical climate, just as the valleys of Switzerland 
have a warm summer though in the immediate vicinity of 
glaciers. It seems probable, also, that the glaciation was 
a southern one, and did not extend far north of the equator, 
if it even reached so far, so that the whole of Venezuela 
and Guiana, with the additional belt of land due to eleva- 
tion, might have been even more luxuriant and more 
densely populated than at present. There would thus 
have been an ample surface to support the ancestors of 
the existing fauna and flora of Brazil during the glacial 
epoch, just as there was sufficient land in Europe to sup- 
port the ancestors of the existing European fauna and 
flora even when so much of the present surface was covered 
by a thick mantle of ice. 
It must be stated that Mr. Hartt does not accept Prof. 
Agassiz’s extraordinary hypothesis (which rests on a very 
slender basis of fact) of a great Amazonian glacier. He 
believes that the wide-spread beds of clays and sandstones, 
which Prof. Agassiz classes as glacial, are marine, and 
states that they agree perfectly with the tertiary beds in 
other parts of Brazil. The patches of drift, with erratics 
in the Amazon valley, may well have been produced by 
detached masses from the glaciers of the Andean and 
Brazilian highlands, which melted and deposited their load 
of drift in the warm waters of the ancient Amazon. 
We have devoted so much of our space to this question 
of the Glaciation of Brazil, in the hope of attracting the 
attention of geologists to a country which offers such an 
interesting subject of inquiry, and which it is so easy and 
agreeable to explore. The facts, as stated by two careful 
observers, both thoroughly experienced in glacial pheno- 
mena, are undoubtedly such as to warrant the main con- 
clusion drawn by them; and it is to be hoped that geolo- 
