80 
The American Geologist. 
Feb. 1890 
II. Mountains, I^rac- 
TURES AND KRUP- 
TiVE Areas. 
1. The Onivchita 
mountains. 
2. The Rocky Trans- 
Pecos mountains. 
3. T h e S h u m a r il 
Knobs and B a 1- 
cones Fracture. 
Disturbed and Pale- 
ozoic sediments and 
igneous material, 
Granites and erup- 
tive. 
P re-Tertiary sed- 
iments. Eruptives, 
etc. 
Lower Cretaceous and 
later sediments. 
Basaltic, and other 
erujjtives. 
Elevated very soon 
after the ciose of 
the Paleozoic. Erup- 
t i V e and slight 
movements at vari- 
ous epochs since. 
Apjjalachian epoch. 
Greatest elevation and 
disturbances in post- 
Upper- C retaceous 
time. Tertiary and 
later. 
Post-Tertiary, proba- 
bly coincident vyith 
the latest disturb- 
ances in the Rocky 
mountain region. 
Balcones epoch. 
[to be continued.] 
ON THE SILURIAN SYSTEM OF ROCKS. 
By Roderick Impey Murchison, F.R.S., 
Vice-President of the Geological and Royal Geographical Societies,* &c., &c. 
Geologists have long felt that the older sedimentary deposits 
required a systematic examination. I have devoted the last five years 
to the study of this class of rocks, hoping thereby to fill up certain 
pages which were wanting in the chronology of the science. (See 
Lond. and Edinb. Phil. Mag. 1832 to 1835, in the Proc. of the Geol. 
Soc] A table published last year was the first attempt to convey to 
the geological student a correct view of the thickness, variety of strata, 
and fossil organic contents of a vast system, which, though arranged 
by nature in the most lucid order of succession, had not previously 
been pointed out. These rocks rising from beneath the old red sand- 
stone in Herefordshire, Shropshire, Eadnorshire, Brecknockshire, 
Monmouthshire, and Ctermarthenshire, and each distinguished by 
separate and peculiar organic remains, were respectively named after 
those localities where each of them could be best studied, and their 
places in the series most clearly established. I have no change to 
announce in the order detailed in that table [see Lond. and Edinb. 
Phil. Mag., vol. iv, p. 370], but I wish to simplify it by the abandon- 
ment of double names, as applied to any one formation, and by the 
adoption of the names of those places only where the respective rocky 
masses lie in juxtaposition. 
The names finally adopted and which will be incorporated in a work 
now in preparation on this subject, are, 
1. Ludlow rocks, divided into upper and lower Ludlow rocks, with a 
central zone of limestone : in this formation no change of name is pro- 
posed. 
*Froni the London and Edinberg Philosophical Magazine and Journal of Science, 
Srd series, July 1835, page 46, [This is the original announcement and description 
of the Silurian system. — Ed. 
