Correspondence—Dr. C. Callaway. 300 
al] the plication or distortion of strata which constitute so important 
a factor in mountain-making, and he is disposed to supplement it in 
the way to which allusion has already been made by Mr. Wynne in 
a recent Presidential Address, viz. by considering the effects of the 
attenuation of strata under superincumbent pressure from deposition 
in subsiding areas, which involves the thickening, puckering, redu- 
plication, and piling up of strata in regions where pressure has been 
lessened. It should be noted that, until disturbance of “cosmical 
equilibrium” takes place, mere pressure does not produce meta- 
morphism. The extent of these lateral movements is described, and 
it is asserted that the theories hitherto adopted to account for plica- 
tion, etc., are inadequate. 
The origin of the horizontal movements is further discussed on 
_the hypothesis that solids can flow after the manner of liquids, when 
they are subjected to sufficient pressure. He considers that the 
displacement in N.W. Scotland may have been initiated by the 
force due to contraction and accumulating in the crust throughout 
the periods marked by the deposition of Torridon Sandstone and 
Silurian stata, the elements of movement finding an exit at the 
ancient Silurian surface. In this case the pile of Silurian strata 
formerly covering the region now occupied by the North Sea and 
part of the Atlantic forced the lowest strata to move laterally, the 
protuberances of the underlying pre-Silurian rocks being also 
involved in the shearing process. Similar results occur in other 
mountain areas. The strata compressed have been greatly attenuated, 
and extended in proportion ; in this way we may account for the piling 
up of strata by contortion in certain regions. The connexion of 
this interpretation with Malet’s theory of volcanoes is also indicated, 
and the author concludes by applying these views to other branches 
of terrestrial physics. 
CORRESPONDENCE. 
——_ 
FOLIATION IN THE MALVERN HILLS. 
Str,—I ask permission to make a brief explanation in reference 
to the debate on General Macmahon’s memoir read before the Geo- 
logical Society on May 22nd. The published summary of the dis- 
cussion attributes to Mr. J. J. H. Teall the statement that, in a 
paper read at a previous meeting, “foliation was actually taken as 
evidence of deformation.” The paper’ here referred to was one read 
by me on April 17th. Taken without qualification, Mr. Teall’s 
remark does not accurately express my views. Nothing is more 
certain than that foliation has been produced in more ways than 
one, and this I have repeatedly said and printed. In the Malvern 
Hills, however, I hold that foliation is always the result of deforma- 
tion. This conclusion is not assumed, but is based upon the fact 
that, wherever the rock lying between an igneous mass and a schist 
is exposed, a gradation. between the two can be traced, and the pro- 
1 See summary of it in Gxonr. Mac. for June, p. 285. The discussion of 
papers, is omitted from the Reports given in the Macazine from want of space.— 
Epit. G. M. 
