REPORT ON THE DEEP-SEA DEPOSITS. 
407 
that the mineral masses in which they are localised belong especially to amygdaloid 
rocks or to the basic series. 
Another very significant fact may be here noticed, viz., that whereas zeolites abound 
in basic volcanic rocks they have no such great development in other crystalline rocks. 
Thus the paste of granites and porphyries, richer in silicic acid than the rocks just 
mentioned, do not contain zeolites, which are replaced by siliceous concretions, by quartz, 
chalcedony, and opal. All this demonstrates in a conclusive manner that the waters 
infiltrated in volcanic masses do not deposit there matters other than those taken up 
from these very rocks, and that the products of the alteration of these rocks furnish the 
elements entering into the constitution of the zeolites or other secondary minerals. 
Water is, then, only an instrument in this regeneration of minerals. At the moment of 
its infiltration it may not have been charged with any of the elements constituting the 
secondary products about to be deposited from it ; these elements are found ready in the 
eruptive masses from which the waters take them to abandon them almost immediately 
in the form of crystals or of amorphous coatings. 
The study of contemporaneous phenomena supports the preceding deductions drawn 
from the observation of eruptive rocks of past geological periods. Daubree has proved 
that at Plombieres water but slightly mineralised has infiltrated into the concrete and 
masonry by whose aid the Eomans had retained the spring, and has there determined the 
formation of zeolites, among which he has observed crystallised phillipsite. In the vesicles 
of the bricks and in the cement, the infiltrating water has deposited minerals identical in 
every respect with those observed in the vesicular rocks of the basaltic series. At Plom- 
bieres better than anywhere else the conditions under which zeolites may be formed are 
easily observed, and it may be there demonstrated with certainty that the waters deposit- 
ing the zeolites take the elements from the surrounding medium. There are no traces of 
zeolites nor of other contemporary minerals in the sandy gravel traversed by the waters 
before reaching the concrete and masonry, and these formations are absent also in the 
friable granite found at Plombieres although submitted to identical conditions as the 
cement and Eoman bricks. We must conclude from these facts, and especially from this 
localisation, that the very material in which the crystals are deposited furnishes to the 
water the constituent elements of zeolites, and it is evidently according to the composition 
or alterability of mineral matters traversed by water that zeolitic matters are extracted, 
deposited, and crystallised. Granite and gravel, richer in silica, offer more resistance to 
the solvent action ; the water cannot take anything away nor depose anything there. 
These modern phenomena then present an exact repetition of those revealed by the study 
of crystalline rocks of geological formations. 
We have given these details of Daubree’s observations at Plombieres, which he has 
found to be confirmed at several other thermal springs, because these phenomena present 
points of comparison which permit us to determine with great probability the origin of 
