1901-2.] J. G. Goodchild on Scottish Mineralogy. 
333 
tion, by the action of non-thermal waters, percolating downwards 
from the surface. Its near ally Wollastonite, however, has not yet 
been proved to occur under any conditions but those connected with 
the metamorphism of lime-bearing rocks by the action of heated 
waters. Epidote and Zoisite occur in like manner. Epidote in 
a large number of cases is certainly due to the thermo-meta- 
morphism of one of the Green Earths, which, primarily, was 
formed by exactly the same process as the Zeolites, and is 
confined to rocks of eruptive origin. Zoisite has in many cases, 
and probably in all, been formed within calcarebus rocks, by 
exactly the same processes as those which give rise to Wollas- 
tonite. Pyrrhotine and Pyrites, again, form a similar parallel. 
All (or nearly all) Pyrrhotine occurs in direct association with 
calcareous rocks which have been affected by hydrothermal action. 
Many other cases of the same kind could be cited. 
Malformation , or irregular development, of crystals. — In the case 
of the great majority of crystals, whether formed by natural 
agency or by artificial means, there is manifested a tendency 
towards the irregular or unequal development of the size of the 
faces of one or more of the forms present. Mineralogists commonly 
refer to this as ‘distortion,’ a term which must strike many persons 
as singularly inappropriate, seeing that the crystal never was of 
ideal habit, and that it has not been forced out of its original 
shape. ‘ Malformed ’ will probably be thought by many to be a 
better term. The malformation itself is clearly due to some 
special cause in operation during the growth of the crystal, 
and the malformation in question is therefore a record of part 
of the history of the conditions under which the growth was 
carried out. That being the case, it would seem desirable to 
preserve the record, in case the feature in question should some 
day prove of value in throwing light upon its own history. It 
seems to be the usual practice, however, in drawing crystals, to 
depict them in ideal symmetry. Nearly all the figures reproduced 
in Heddle’s Mineralogy of Scotland are thus represented. The 
objections to the practice are, that in restoring ideal symmetry, an 
important piece of evidence relating to the history of the crystal 
has been wiped out; and, what is of still more importance, the 
