266 The American Geologist. October, i«93 
yte, dacyte, rhyolyte, pyroxene andeByte, and basalt. The lavas dis- 
play a great variety of volcanic products in both chemical and mineral 
composition. They are all derived from a common source, a homoge- 
neous molten mass. They are due to a process of differentiation by 
molecular change within the molten mass under varying conditions of 
pressure and temperature. Starting with a magma of intermediate 
composition, the extreme products of such a differentiation are 
rhyolyte and basalt. 
The ores of the district are in rocks of the Cambrian, Silurian and 
Devonian periods, extending through 17,000 feet of strata, the most 
productive being found in the Cambrian, this not because of their 
geologic age, or their chemical constitution, but rather because of 
greater proximity to favorable structural conditions. The ores are 
later than the rhyolytes and consequently are of Pliocene or post- 
Pliocene age. They originated from below, and were accumulated as 
sulphides. They were subsequently oxidized by atmospheric agents, 
mainly surface waters percolating through the rocks. 
Systematic lists of fossils are given by Mr. Walcott in an appendix. 
Microscopical petrography is discussed by Mr. Iddings in another 
appendix, illustrated by several plates. 
The Geology and Paleontology of Queensland and Neiv Guinea. 
Robt. L. Jack and Robert Ethekidge, Jr. 68 plates and a geological 
map of Queensland, in six sheets. Two volumes, text and plates, 1892. 
Brisbane and London. (Dulau & Co.) 
While the collection of the material and the stratigraphical studies 
in the field have been done mainly by Mr. Jack, the purely paleontolog- 
ical work has been done more recently by Mr. Etheridge. By their 
joint labors a very valuable publication has resulted. The aim is to 
collect into a compact, systematic form all that is known both of the 
stratigraphy and of the paleontology of Queensland. The map which 
accompanies the work will prove a very great addition to the geological 
literature of Australia, while the fine plates of fossils will fix, forever, 
the paleontological values of the data on which nearly all the conclu- 
sions of the authors are based. 
There are no recognized fossiliferous terranes older than Devonian, 
although there is a large series of metamorphic slates and schists, as 
well as of granites and gneisses, estimated at over five miles in thick- 
ness, whose age is undetermined. The suggestion has been made that 
these embrace some of the Cambrian and Silurian, but no fossils 
have been discovered to reveal their age; Mr. Jack is inclined to the 
opinion that the greater portion of them will prove to be of Permo-Car- 
boniferous and Devonian. Yet some of them are overlain by Devonian 
rocks containing characteristic fossils (p. 23), and in the map attached 
to the report the metamorphic rocks are classed provisionally as Lower 
Silurian. 
The fossils named are chiefly those that have before been described 
in papers published in various places by Owen, Etheridge and Car- 
