TRANSACTIONS OF THE SECTIONS. - OF 
mountain limestones, and many persons had been in the habit of regarding the ore as 
of the same age as the mountain limestone, and as being part of the limestone series ; 
but a careful observation of the district of North Lancashire would go far to remove 
this opinion. Running across the mountain limestone of that district were vast and 
often devious hollows, and it was in these hollows that the ore is found, lying upon 
the limestone, and resting on one side against what was evidently a great line of fault, 
as well as in the fissures and hollows of the rock, with all the indications of a Jater 
deposit. ‘The communication of Mr. Baker showed by very exact sections and de- 
scriptions, that iron ore was not confined to limestone, but was also to be found in con- 
nexion with the adjacent slate formations, showing that it was not a deposit peculiar to 
the limestone. The opinion which Professor Phillips had formed on this subject he by 
no means wished to be accepted as a positive conclusion; but the position of the ore, 
upon the faults of the limestone as well as in the fissures and hollows of the rock, went 
to prove that it was astbsequent formation. ‘The date to which it could with most pro- 
bability be referred was that of some parts of the Permian deposits. He was inclined 
to belicve that the lines of faults and fissures, and the sinuous hollows, sometimes 
cayernous, in the limestone, which had been excavated or modified by water, were 
due to the action of causes which preceded the period of the Permian system, and 
that the iron formation might generally be referred to the age of the Permian rocks, 
and occasionally to a still later date, namely, that of the New Red Sandstone, He 
was satisfied that the iron ore of Lancashire and Cumberland could not with proba- 
bility be referred to the period of the mountain limestone. 
On a New Method of determining the Temperature and Pressure at which 
various Rocks and Minerals were formed. By H.C. Sorsy, #.RS. 
If a tube be filled with air at any particular temperature and pressure, and be after- 
wards taken to a place where the temperature or pressure is different, the change in 
the volume of the air would enable us to calculate the difference in the temperature, 
if the difference in pressure were known, or to ascertain the difference in the press- 
ure, if the difference in the temperature were known. Where crystals are artificially 
formed from solution in water, they catch up and hermetically enclose in their solid 
substance small quantities of that liquid, so as to produce fluid-eavities, which, from 
the nature of the circumstances under which they originate, are just full of the liquid 
at the temperature and pressure at which they are formed. This fluid is also affected 
by changes in temperature and pressure, only that of course the actual amount of the 
change of dimensions and the laws connecting it with the temperature and pressure 
are not the same as in the case of air. If, then, a crystal be formed at an elevated 
temperature, but under no very great pressure, when it cools down to the ordinary 
heat of the atmosphere, the fluid in these cavities contracts, so as to leave a vacuity, 
the relative size of which must of course depend upon the height of the original 
temperature. Such fluid-cavities are easily seen with a suitable magnifying power, 
and the relative size of the vacuity can be measured by means of the micrometer. 
Applying these principles to the study of natural crystals, it is found that, whilst some 
indicate a temperature not materially higher than that of the atmosphere, many must 
have been formed at a heat rising upwards to that of dull redness, which is especially 
the case with igneous and metamorphic rocks. If, however, the crystals were formed 
under a very great pressure, of course the above conclusions would be invalidated, 
and the calculated temperature would be too low; but if we could form some approxi- 
mation to the actual temperature, we could deduce, from the relative size of the 
vacuities in the fluid-cavities, the pressure under which the crystals were generated. 
Where the fluid-cavities in granite rocks are studied in this manner, they lead us to 
conclude that such rocks were formed under a very great pressure, varying in different 
cases, but of such a magnitude, as clearly points to their deep-seated, plutonic origin, 
On some Peculiariiies in the Arrangement of the Minerals in Igneous 
Rocks. By H.C. Sorsy, &.RS. 
In both recent and ancient igneous rocks, it is not at all unusual to find crystals of 
a mineral that fuses at only a moderately high temperature, acting as the nuclei on 
