Review of Rece?it Geological Literature. 31 1 
An important element in this report, as in any properly prepared 
report on a district where mineral wealth probably exists, is the pre- 
sentation of a geological map, accurate in as far as exposures will al- 
low, which indicates definitely the areas where there is no prospect 
of finding ore deposits and those in which exploration may be suc- 
cessful. In the Crystal Falls district scarcity of outcrops has ren- 
dered this work difficult, but the mapping out of several lines of mag- 
netic attraction where there are practically no exposures has greatly 
increased*the value of this report from an economic point of view. In 
fact the reviewer understands that certain explorations, made since 
the field work was completed and made in localities indicated by the 
authors of this report, have been successful. t'. s. G. 
Upper Silurian Faima of the Rio Troiiibetas, Province of Para, 
Brazil. (Archives do Museu Nacional do Rio de Janeiro, vol. X, 1897- 
i8q9, 48 pages, 2 plates), and Devonian Mollusks from the State of 
Para, Brazil. (Ibid.. 125 pages, 5 plates). By John M. Clark^. 
Dr. Clarke expressed several years ago, in a conversation, his dis- 
appointment at the fact that two manuscripts of his containing the 
descriptions of interesting Brazilian faunas had probably been lost in 
that country. It is highly gratifying that this has not happened; for 
the papers, af^er having been comfortably asleep in the drowsy tropic- 
al climate for almost eight years, have suddenly become awakened 
and presented in a handsome volume, bringing with them the infor- 
mation that the copies for distribution may soon arrive. As the 
papers bear the dates of December 10, 1891, and April 25, 1892, it is 
obvious that some of the discussions which they contain have been 
superseded by later publications, a circumstance that is apt to some- 
what diminish the author's pleasure at the recovery of these already 
given-up children. 
Both papers are printed in the Portuguese and English languages. 
The fauna described in the first paper was discovered in yellowish 
micaceous sandstones on the Trombetas river, a northern tributary 
of the lower Amazonas. during the existence of the Geological Survey 
of Brazil, and were placed by Dr. O. A. Derby in ]Mr. Clarke's hands. 
The collection contained, besides the fossils from this sandstone, a 
fucoid from a gray sandy shale from Oiteiro do Cachorro. which 
proved to be identical with the well-known Arth-cphycus harlani 
Conrad, of the Medina sandstone. 
The yellowish sandstones abound in fragments of spicules of hexa- 
stinellid sponges and in brachiopods. .\mong the latter are a Lingula 
which exhibits the characters of the L. oblata of the Clinton; and a 
new Lingulops (L. derbyi). represented by a beautifully preserved 
internal cast of one of the valves, which permits some interesting ob- 
servations in regard to the structure of this fossil and the development 
of the Lingulas through Lingulops into the Trimerellidie. This par- 
ticular form of Lingulops seems to be most nearly related to the 
species described from the Hudson River shales. There was further 
found an Orbiculoidea (O. hartti), which does not show any relation 
