70 RICHTHOFEN — NATURAL SYSTEM 
form ‘‘ trap rocks” and ‘‘lava.’’ One common cause is thus assigned to both meta- 
morphic and eruptive (including volcanic) action, the latter being considered an ad- 
vanced stage and ultimate result of the former. The immense action of metamorphism 
is an undeniable fact. But while formerly, on account of the violent agencies which 
were supposed to have been required for it, and the growing conviction that heat alone 
could not produce effects on such an enormous scale as had been suggested, the sub- 
ject had to be treated with caution, and any extreme assumption was received with 
doubt, if not with a certain repulsion, the condition of things, in this respect, has of 
late undergone a great change, as scientific experiments, and especially those of Dau- 
brée, have demonstrated the extent of the influence of water and pressure in producing 
metamorphic action. They have proved the remarkable fact that, at a comparatively 
low temperature, and with the aid of pressure, the effects of water, if continued for a 
sufficient time, particularly when it is charged with alkaline substances, will be able 
to produce changes in the nature of rocks which surpass even the most audacious 
assumptions of former time. An apparently safe foundation was now given to the 
widest generalizations, and the consequence is, that an almost unlimited action is at the 
present time brought to the account of metamorphism. The least founded concep- 
tion, however, of the faculties ascribed to it, we consider to be its supposed sole in- 
strumentality in the production of volcanoes and the eruptive action of former ages 
from portions of the shell of sedimentary rocks. It is true that a great additional 
degree of apparent probability has been given to the metamorphic theory of eruptive 
rocks by the results of the microscopic examination of rocks so successfully instituted 
by Sorby, since they prove a remarkable similarity, in the minutest texture, of the 
minerals constituting granite and some cognate non-foliated rocks, with the main in- 
gredients of certain foliated rocks made up of silicates, such as gneiss and micaschist. 
These had been observed long before to form the last link of a series which may be 
traced, by slow gradations, from unmetamorphosed sedimentary rocks, through those 
which are undoubtedly metamorphosed, up to the crystalline foliated rocks mentioned. 
The newly discovered facts appeared to indicate that granitic texture is the most ad- 
vanced stage in a progressive series of molecular changes, and, carrying the argumenta- 
tion still farther, the assumption was apparently justified that a corresponding origin 
must be ascribed to other rocks, such as those of volcanic origin, which are connected 
with granite by another long and gradual line of passage. 
In drawing up our argument against this theory, (including all those doctrines 
23 It may be frequently noticed, that those eminent men who, by creating a firm basis for induction, have pointed 
out the path through regions in the field of science the knowledge of which had consisted before of a confused accumula- 
tion of facts and suggestions, did themselves apply the newly acquired views within moderate limits, while sweeping general- 
izations on the same basis were usually made by others. It is so in the present case. The limits within which Daubrée 
himself has applied his ingenious conclusions from his experiments on the action of superheated water and pressure upon 
silicates, will probably never be drawn any closer. No discovery, however, could have been more opportune to those who 
had advocated before the origin of eruptive by the remelting of sedimentary rocks. Against the form of this theory which 
was first proposed by Hutton, and enlarged by Lyell, Babbage, Herschel and others, similar objections could be raised as 
against that form of the theories of the first class which was held by Buch. With the aid of the new views acquired, 
however, it was remodeled and brought into its present shape. A far greater extent is thus being given to the conclusions 
from Mr. Daubrée’s experiments than their author ever intended. 
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