32 Proceedings of the Royal Physical Society. 
And if our ideas of a mineral species be thus overturned, 
so will the consequent classification into orders and genera. 
In the re-arrangemeut of our mineral orders, it may be found 
expedient to include their derivative rocks. Thus, observers 
may afterwards find that peculiar minerals characterise cer- 
tain classes of volcanic rocks, whilst the metamorphic rocks 
are the special habitat of others, and the sedimentary or 
organic of yet different varieties. This would thus involve, 
that our treatises on mineralogy contain likewise much more 
of petrology than they ever have done. 
The examination of what is given in our mineralogical 
treatises as the seventh order, the Inflammables, will show 
how artificial our present classification is. In it we have 
sulphur, coal, the resins, the inflammable salts, minerals no 
doubt possessing one physical character in common, but 
differing wide as the poles asunder in their other characters. 
Nor are the subdivisions of the order more satisfactory, as 
is well known from the repeated recurreuce in our legal 
courts of the qu.estion, "What is coal?" Chemistry has been 
mainly relied on in considering this query. But a little 
stud}^ of the order will convince us that the foundations on 
which we build our individual discriminations of the various 
minerals must be physical and not chemical. A close 
chemical analogy subsists betwixt minerals of the order 
otherwise manifestly of very different properties. Thus, 
certain varieties of bitumen and cannel coal are nearly 
identical in chemical composition. Again, peat, coal, the 
bitumens, the ambers, are all under the same chemical cate- 
gory. But reasoning based on such an analogy may lead us 
into serious practical mistakes. Thus it has been generally 
assumed that bitumen and coal were of vegetable origin. 
Now, it has been indisputably proved that the petroleum of 
Canada is of animal origin — the animal remains of the coral 
builders of the Silurian and Old Eed Sandstone reefs of the 
American continent yielding the material whence it is 
derived. Again, many shales must have obtained their 
bituminous character from animal remains, as is shown both 
by their imbedded fossils and their juxtaposition with lime- 
stone beds, richly fossiliferous. Some shale beds are en- 
