276 
ELUCIDATION OF “ TRANSITION” ROCKS. 
we can see the window-post clearly. The 
second figure is inverted, and appears before 
the opening ; it is more indistinct than the 
first. These appearances belong to the phe- 
nomena of diffraction. The form which the 
charcoal assumed, by the powerful heat 
applied in the manner described, is similar to 
the filamentous nmatter examined by Dr. H. 
Colquhoun, which was obtained during some 
trials made by Mr. Macintosh to convert iron 
into steel, by surrounding it with coal gas in 
an air tight iron chest.* 
RECENT RESEARCHES IN GEO- 
LOGY. 
Geology is a subject of immense extent ; 
and the discoveries which are made in it al- 
most necessarily proceed by slow steps and 
minute details. Hence it would be utterly im- 
possible, even in a memoir of considerable 
length, to give a complete and comprehensive 
survey of the recent progress of this rapidly 
advancing Science. But here, as in all sound 
inductive researches, the accumulation of par- 
ticular facts generally terminates, aftera while, 
in the development of some great general 
principles. When such epochs occur, it it often 
very practicable to condense into a short com- 
pass, and in a generally intelligible form, a 
statement of the results so obtained. This 
is what we shall attempt, in the following 
article, with respect to one or two leading sub- 
jects of geological inquiry, which have not 
only excited peculiar interest of late, but also 
have important bearings on the principles of 
Science, and on some of the most instructive 
inferences and contemplations into which we 
are led by the study of it. 
The conclusions of geology, like those of 
every other part of inductive science, must be 
grounded on the sole authority of well-ascer- 
tained and classified facts ; and we must be 
guided to them, neither by random conjec- 
tures, nor the dictation of authoritative opi- 
nion, but by the so/e pursuit of well-founded 
natural analogies. We must seek to interpret 
the past from the present, and advance from 
the known to the unknown. 
Proceeding on such principles, then, we 
shall presume that our readers will acknow- 
ledge the force of the reasoning by which it 
is inferred that where two beds, or strata, lie 
one over the other, the former was deposited 
or formed subsequently to the latter ; that 
each one of the vast number of lesser beds or 
layers, of which even a small thickness of 
any stratum is composed, were all formed one 
after another; and, when we come to dis- 
tinguish the larger divisions and classes of 
strata, by the fossil remains of plants and 
animals, which we find imbedded, and often 
completely mineralized in them, — that these 
* PoggendorflTs Ann. xxxv. 468. — Thomson’s 
Inorganic Chemistry, i. 160. 
are the remains of creatures which actually 
lived and died during the period at which the 
depositions took place respectively ; and that 
the lowest rational estimate we can form will 
not allow U3 to suppose any short or limited 
period of time as requisite for the formation of 
any one bed, the enclosing in it of all its 
organic remains, and (marine or aquatic as 
those remains so universally are) its elevation 
from the bottom of the primaaval ocean into 
dry land. 
Pursuing our researches on these simple and 
truly philosophic principles, we are brought 
in succession to recognise an immense series 
of deposits, characterized by organic remains, 
in which the skill of the naturalist and the 
anatomist detects species, genera, entire orders 
of living beings which do not now exist. The 
deposits in which these occur, now in a great 
degree hardened and consolidated into rocks, 
are thus characterized as distinct formations 
which have gradually emerged at sticcessive 
remote epochs, at incalculably long intervalsof 
time. Other classes of phenomena are obser- 
vable in a series of rocks of a different texture, 
and wholly destitute of organic remains, which 
appear protruded, as it were, among and 
through the others : having, in many cases, 
an exact resemblance to the effects of exist- 
ing volcanoes, — and in all, following a close 
analogy to such modes of eruptive action. 
We shall in the following sketch presume 
no further on our reader’s acquaintance with 
the subject than to the extent here briefly 
descr ibed. The names given to the successive 
leading groups of formations, which all over 
the world succeed one another in this order, 
are principally, the tertiary (or newest), 
above the chalk. The secondary, from the 
chalk inclusive to the coal formations : then 
those whrch have been called transition ; and, 
lastly, the primary, of crystalline texture, 
without organic remains, and bearing marks 
of being upheaved, protruded, or forced 
through all the others, in the way that mass- 
es of melted matter are now forced up by 
volcanic action. 
SILURIAN AND CAMBRIAN FOR- 
MATIONS. 
Mr. Murchison and Professor Sedgwick 
have been for a long time directing their joint 
labours to the elucidation of the rocks usually 
confounded together under the unmeaning 
name of “ Transition,” comprising all the se- 
ries intervening between the old red sand- 
stone and the primitive rocks. They have 
been minutely examined by these two eminent 
geologists, as developed in Wales and the 
part of England adjoining, and they have suc- 
ceeded in dispelling almost entirely the ob- 
scurity in which the nature of these rocks has 
been long involved. 
From beneath the old red sandstone, there 
rises out this considerable group of rocks, 
which, taking them in the order from upper 
to lower, Mr. Murchison has named the 
Ludlo, Wenlock, Caradoc, and Llandeillo 
formations, each being distinguished by cha- 
racteristic organic remains, and frequently by 
subordinate beds of limestone, 'i hese beds 
form a well-marked connected group, inter- 
