Correspondence—M. G. H. Morton. 95 
ejectamenta of volcanos. These and other phenomena, such as that 
which I shall shortly mention, have been too much ignored by 
mathematicians in treating of the subject. To suit the exigencies of 
the calculus, they assume the earth to be homogeneous throughout, 
and either fluid, viscous, or elastic, and take no account of any 
greater rigidity existing in the surface than in the parts beneath it. 
Mr. Darwin, for example, in his paper on the Stresses of Continents 
and Mountains, assumes that the earth must be strong enough to 
bear the stress arising from their weight. But it is a fact well 
known to geologists that the parts of the earth’s surface which have 
a tendency to sink are not the mountains, but the sedimented areas, 
the river plains, and the bottoms of shallow seas. ‘The tendency of 
the mountains, on the other hand, is to rise, so as partially to com- 
pensate for what they lose by denudation. In short, the crust of the 
earth bears a close analogy to a floating field of ice, broken up, crushed 
together, and refrozen; and no one would argue that there could be 
no fluid stratum beneath it, because some blocks of ice stood higher 
than others; for he would know they would receive sufficient support 
from their under sides sinking deeper into the water. 
The above facts show that the substratum must have a less 
viscosity than the crust. But if the substratum be as rigid as glass 
or steel, then the crust must be much more rigid than glass or steel, 
which is a reductio ad absurdum. For my own, part I believe it to be 
what may without impropriety be called liquid. And if it be asked 
how it can remain liquid under the pressure of between 20 and 30 
miles of superincumbent solid rock, I answer, that recent experiments 
have tended to show that igneous rocks are denser when melted than 
when solid at the melting temperature. Consequently we may expect 
their melting-point to be lowered rather than raised by pressure. 
If that be the case, solidity would not be induced in such molten 
rocks by the pressure of the superincumbent crust. 
Hartton, CAMBRIDGE, O. FISHER. 
5th January. 
PERMIAN AND TRIAS OF SOUTH-WEST LANCASHIRE. 
Srr,—Having read the recent articles on the Permian and Trias by 
the Rev. A. Irving, F.G.S., and the letters referring to the Permian 
strata of South-west Lancashire, I beg to offer some further informa- 
tion more recent than that available to Prof. Hull, Mr. De Rance, 
or Mr. Strahan. During the last week I visited St. Helen’s Junction, 
and in consequence of a fall of débris at the side of a pit, found an 
exposure of ten feet of red marl, containing a layer, a few inches 
thick, of a greenish colour which effervesces strongly in acid. IJ and 
Mr. Strahan saw the sandstone at the base of this section in 1881, 
but at that time only one foot of the overlying marl was visible. 
No fossils have been found, or searched for, it being dangerous to 
approach the spot for fear of falling into the pit. The marl must 
belong to the beds described in the wells of the brewery many years 
ago, and most likely represents the Permian. 
However, a section of much more importance has just been 
