146 
Review of Recent Geological Literature . 
out asking the assent of a heterogeneous organization which 
cannot know what is best for geological interests. It is ear¬ 
nestly to be hoped, however, that in arriving at its official 
utterances, the counsels of its first president will be studiously 
heeded. This result will be attained if each fellow forbears to 
push, against the will of a majority, ends in which he feels a 
special, or perhaps a personal interest; and if the minority find¬ 
ing itself such, will yield gracefully to the sentiment of the 
superior number. Pax nobiscnm ! 
REVIEW OF RECENT GEOLOGICAL LITERATURE. 
Useful Minerals of the United States. By Albert Williams, Jr. This 
paper, embracing pages 688 to 812, is an abstract from “ Mineral Resources 
of the United States, Calendar Tear 1887” 
Under the head of useful minerals, etc., is a partial list Of ores, minerals, 
and mineral substances of industrial importance, arranged alphabetically by 
states and territories. 
Of the facts presented in this report, among the most encouraging in 
connection with the settlement and development of our Northwestern 
States and Territories, is the occurrence of the extensive coal deposits of 
Colorado, Dakota, Montana, Nevada, New Mexico, Oregon, Utah, Wash¬ 
ington and Wyoming. The coal is chiefly of Cretaceous or post-Creta¬ 
ceous (Laramie Group) age, and appears as lignite, bituminous coal, semi- 
bituminous coal, or anthracite. The bituminous and anthracite coals of the 
west are, in many cases, equal in grade to the corresponding varieties from 
the Carboniferous series of Pennsylvania. Few who have not seen them 
can have any conception of the extent and value of these magnificent 
coal deposits. 
The Structure and Development of the Visual Area in the Trilohite , 
Phacops rana Green. By John M. Clarke. [Reprinted from the Journal 
of Morphology, vol. ii., No. 2, November, 1888.] Barrande, Walcott, Pack¬ 
ard and a number of others whose names are familiar to geologists, have 
devoted attention to t ; e elucidation of certain peculiarities of structure or 
development among tribolites. The efforts of these observers have been 
attended with remarkable, and often with unexpected success. The author 
of the paper here reviewed devotes his attention chiefly to one species, and 
to one feature—namely: the development of the visual area. Mr. Clarke 
divides tribolites into two groups, according to the character of the visual 
area. The first includes those having the visual area covered by a smooth, 
continuous, epithebial film or cornea through which the lenses of the om- 
matidia are visible by translucence; the second, those in which the cornea 
is transected by the protrusion of the sclera. The author had at command 
some thousands of specimens for study. For convenience he regards the 
