330 The American Geologist. May, 18&1 
City, Colorado, by Mr. T. W. Stanton. The find was so surpris- 
ing that a second collection was made from the same place and as 
it confirmed the previous deduction Mr. Walcott himself went out 
to the spot in December last and on examination found that the 
bed from which the remains had been obtained lay about 180 feet 
below others containing well characterized invertebrates of Tren- 
ton age. He therefore concludes that the existence of fish in 
the Trenton series is established. 
It is worthy of note that Mr. "Walcott's fossils indicate the 
presence of elasmobranchs as well as of placoderms and in that 
respect confirm previous observations. Should his suspected 
demonstration of notochordal relics among his fossils prove correct 
it must remove all doubt regarding the vertebrate nature of these 
earliest known fish. 
It now remains for some one to discover the ancestors of these 
Trenton fish in rocks of older date for it is not possible to believe 
that the} T were the primeval vertebrates. 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
The Petrography and Structure of the Piedmont Plateau in Maryland. 
By George Huxtixgtox Williams, of Johns Hopkins University. With 
a supplement on A geological section across tlie Piedmont Plateau in 
Maryland. By Charles B. Keyes. Bulletin, G. S. A., vol. ii, pp. 301- 
318, with a plate map, and two sections in the text ; and pp. 319-322, 
with three figures in the text : March 15, 1891. The rocks of the west- 
ern part of the Piedmont area in Maryland are semi-crystalline, con- 
sisting of phyllites, sandstone, and marble, with very scanty eruptive 
rocks, the last being represented only by Mesozoic diabase or by serpen- 
tine whose origin is still in doubt. The eastern part of the area is 
strongly contrasted with the foregoing, as it consists of highly crystal- 
line rocks, including sedimentary gneisses, quartzites, and dolomite, and 
eruptive rocks of very great variety and abundance. 
Professor Wiliams writes ; "Bocks whose eruptive origin is either 
undoubted or most probable cover at least half of the now exposed sur- 
face within the eastern or more crystalline area. A much less propor- 
tion can be assigned with any degree of probability to sedimentary 
formations, while the remainder possess the characters of both classes 
to such a degree that their origin must still be considered as unde- 
cided." In many places the eruptives "have suffered hardly less com- 
plete foliation and metamorphism than the sediments which surround 
them, while in both this action is far in excess of what has taken place 
in any portion of the western area." 
