284 Recent Literature, [ April, 
cotton belt, though most of the moths die off in the autumn. 
The insect parasites, twelve in number, which prey upon them 
are described, while a large part of the Bulletin is taken up with 
the various remedies employed, of which Paris green, London 
purple, these being preparations of arsenic, are strongly advocated, 
and a number of machines and contrivances for sprinkling and 
spraying dry and liquid poisons are figured and described. The 
work will be of great use to cotton planters; and to entomologists 
the entire ee a a its skillful mode of treatment will render it 
of permanent valu 
GILBERT'S GEOLOGY OF THE HENRY Mountatns.\—The teacher 
as well as student of general geology in this country who would 
be at all informed as to the broader features of American geoloty 
and paleontology is compelled to resort to the magnificent series 
of reports of our geological surveys of the Western Territories. 
These, almost without exception, have been ably prepared, and in 
most beg certainly worthy of the time and money bestowed 
upon the w rom them have been and will be largely de- 
rived the materiale for our text books. The present monograph, 
though not bulky, is a finished and elaborate study of an interest- 
ing group of mountains forming one of the western outlines of 
one of the flexures of the Rocky Mountain range, and rising sud- 
denly from what has otherwise been a region of geological calm. 
This group of five elevations forms as many daccolttes, as the au- 
thor terms them. It is usual, he says, for igneous rocks to as- 
cend to the surface of the earth and build up mountains or hills by 
successive eruptions. Such are volcanoes. Now, when the lava, 
instead of rising through all the beds of the earth’s crust, stops 
at a lower horizon, and insinuates itself between two strata and 
opens for itself a chamber by lifting all the overlying stfata, and 
here cools, forming a massive body of trap, a laccolite (daccos, 
cistern, and lithos, stone) is formed. This is the mode in which 
the Henry Mountains were formed, as well as numerous other 
isolated groups in the Plateau region. That many similar peaks, 
with the Elk mountains of Colorado, elaborately described by 
Messrs. Holmes and Peale, of Hayden’s Survey of the Territories, 
were formed in an identical manner has been independently estab- 
lished by these geologists, as stated by our author. 
Gilbert also makes the generalization that there are two types of 
igneous rock. ‘One type of rock is acidic, including porphyritic 
trachyte and eruptive le and its occurrence is, without ex- 
ception, intrusive. The other type of +rock is basic, including 
basic trachyte and basalt, nnd its occurrence is almost uniformly 
extrusive.” It appears that each group of laccolites is composed 
1 Department of the Interior. U. S. Geographical a Peet me Survey of the 
Rocky oe Region. Report on the Geology of the Henry Mountains. BF: G 
G. K. GILBERT. Washington, 1877. {Received Nov. i, 1879.) 4°, pp. 160. ae : 
plates and Gooti = 
