OBJECTIONS TO METAMORPHIC THEORY. 
587 
That large portions of the plutonic rocks had been formed 
under the influence of such intense heat is in perfect accord¬ 
ance with their great volume, uniform composition, and ab¬ 
sence of stratification. The forcing also of veins into con¬ 
tiguous stratified or schistose rocks is a natural consequence 
of the hydrostatic pressure to which columns of molten mat¬ 
ter many miles in height must give rise. 
Objections to the Metamorphic Theory considered. —It has 
been objected to the metamorphic theory that the crystal¬ 
line schists contain a considerable proportion of potash and 
soda, whilst the sedimentary strata out of which they are 
supposed to have been formed are usually wanting in alka¬ 
line matter. But this reasoning proceeds on mistaken data, 
for clay, marl, shale, and slate often contain a considerable 
proportion of alkali, so much so as to make them frequently 
unfit to be burnt into bricks or pottery, and the Old Red 
Sandstone in Forfarshire and other parts of Scotland, de¬ 
rived from disintegration of granite, contains much tritu¬ 
rated feldspar rich in potash. In the common salt by which 
strata are often largely impregnated, as in Patagonia, much 
soda is present, and potash enters largely into the composi¬ 
tion of fossil sea-weeds, and recent analysis has also shown 
that the carboniferous strata in England, the Upper and 
Lower Silurian in East Canada, and the oldest clay-slates in 
Norway, all contain as much alkali as is generally present 
in metamorphic rocks. 
Another objection has been derived from the alternation 
of highly crystalline strata with others less crystalline. The 
heat, it is said, in its ascent from below, must have traversed 
the less altered schists before it reached a higher and more 
crystalline bed. In answer to this, it may be observed, that 
if a number of strata difiering greatly in composition from 
each other be subjected to equal quantities of heat, or hy¬ 
drothermal action, there is every probability that some will 
be much more fusible or soluble than others. Some, for ex¬ 
ample, will contain soda, potash, lime, or some other ingredi¬ 
ent capable of acting as a flux or solvent; while others may 
be destitute of the same elements, and so refractory as to be 
very slightly afiected by the same causes. Nor should it be 
forgotten that, as a general rule, the less crystalline rocks 
do really occur in the upper, and the more crystalline in the 
lower part of each metamorphic series. 
