REVIEWS 667 
and in the Great Antilles is directly in harmony with the east and west 
trend of the same phenomena upon the mainland, and we cannot 
escape the conclusion that they are the product of the same great oro- 
genic revolution, the age of which was mid-Tertiary, for rocks of early 
and late Eocene (and Oligocene) age everywhere, as exposed along 
the Caribbean coast, and in the Great Antilles, are folded by these 
mountain-making processes, while the Pliocene and Pleistocene are 
more horizontally laid down against the seaward margin of the moun- 
tain masses.” 
It is worth noting that the great orogenic movements of this 
region, dating from the later part of the Miocene, are in harmony 
with the great disturbances which took place in several continents at 
about the same time. They furnish a significant commentary on the 
infelicity of the current grouping of the Miocene and Pliocene under 
the common name Neocene. Nearly everywhere outside the regions 
of glaciation, the Pliocene and Pleistocene are more closely associated 
than the Miocene and Pliocene. The above use of the term Neocene 
makes this pertod mame cover an interval of time in the midst of which 
occurred one of the most profound physical revolutions to which the 
earth’s crust has been subject. For such use of the term there is but 
one analogy in the nomenclature of post-Algonkian time, namely, 
that of the use of the term Silurian, to cover all beds between the 
Cambrian and Devonian, although in the midst of this division 
occurs the greatest break, both stratigraphic and palzontologic, in 
the whole Paleozoic. The other physical revolutions comparable to 
that which took place at the close of the Miocene mark not simply the 
close of periods, but of eras. 
In post-Miocene time, or perhaps accompanying the orogenic 
movements referred to, there was epeirogenic uplift and erosion, fol- 
lowed by moderate subsidence, and still later by uplift of slight extent, 
converting the shallow margin of the sea into low-lying coast lands. 
The igneous rocks of the region appear to have a wide range in 
age. The age of the granitic mountains of east-west trend is not 
known, but they seem to be mainly pre-Tertiary, and probably pre- 
Cretaceous. Some of them may be much older. The later igneous 
rocks of the region seem to date in part from the later part of the 
Cretaceous period. Here belong the rhyolitic tuffs of the Panama 
formation which is believed to be pre-Tertiary. In the early Tertiary 
also there was great volcanic activity, but whether the vulcanism of the 
