PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. Dal 
nesia, by magnesian waters, and the consequent increment of that material in 
the product, such an operation acting by itself could never accomplish the 
necessary transformation. Pre-existent constituents have to be abstracted, and 
the mere abstraction of these, without any direct insertion of magnesia, will, 
of itself, by the consequent proportional incrementation of the non-abstracted 
magnesia, suffice to determine the required change. 
While it is much to be desired that a still more extended series of analyses 
be undertaken to throw more light on this matter, a glance at the tabulated 
results of the analyses of these alteration products will show that no incon- 
siderable amount of information is afforded to us thereby. 
These results demonstrate that the process of change consisted, in progres- 
sive order— 
First, in a direct increment of the water. 
Second, in a decrement of the lime. 
Third, in a gradually increased decrement of iron. 
Fourth, in a decrement of silica. 
In some situations, however, there is no decrement in the iron, but a 
peroxidation thereof. 
What the rationale of the change under the jirst of these heads may be, I 
could not, in the circumstances of so small an amount of matter to found on, 
attempt to show. 
What were the circumstances under which minerals, usually inert as regards 
any tendency to become hydrated, assumed to themselves, often without any 
appearance of alteration, so large a quantity of water, we do not in any measure 
know. 
The circumstances under which some at least of the other changes may be 
effected we do know; and our knowledge thereof may be grouped under 
certain heads. 
And here it may be remarked, that unless we are able to show, upon 
recognised chemical principles, the mode in which one rock mass may be trans- 
muted into another, we are still within the region of mere speculation. 
The leading summary of our knowledge may be stated thus :— 
The primary agent of change is meteoric water, holding carbonic acid and 
oxygen in solution. 
The secondary agent is spring water, holding less oxygen, more carbonic 
acid, and certain salts in solution. 
The third agent is these same waters, sinking downward or rising upward, 
but now holding more complex salts—the products of the first operation of the 
_ waters themselves,—these salts being the agents of a second set, perhaps an 
endless cycle of changes, generally more potent than the originals. 
As regards the substances operated on, we know that those most easily 
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