36 
ORIGIN OF BEDS OF GYYSUM.—LEAD. 
acid, or with sulphate of iron, derived from the decomposition of pyrites. When such a mix¬ 
ture of acid and water passes downwards through the strata, and comes into contact with carbon¬ 
ate of lime, either disseminated in the strata or in the form of beds, it produces decomposition, 
and the sulphate of lime is formed, which crystallizes either at the place of decomposition, or at 
a still lower point, where the gypseous solution accumulates. This accumulation or concentration 
of the percolating fluid may be caused by the presence of a layer of impervious clay, which 
prevents its further progress. When the infiltrating fluid is charged with sulphate of iron, a 
double decomposition ensues, sulphate of lime and carbonate or oxide of iron being formed; the 
latter being deposited at the point of decomposition as a red or brown powder. The origin of 
the red marls and sandstones may be thus explained. I do not doubt the formation of many 
gypsum veins and thin layers in this manner—hy the infiltration of acid water, and the subse¬ 
quent and gradual crystallization of the solution in the strata, separating itself in clear plates 
from the earthy materials which hold the solution. This is accomplished by the crystalline 
forces, precisely as water in crystallizing in a bank of earth and sand will separate into clear 
sheets of ice with such tremendous force as to elevate banks of superposed earth many feet thick. 
If a thin seam of selenite or ice may be formed in this manner, it is not unreasonable to believe 
that beds many feet thick may have the same origin. A larger supply of material only is 
required. Abundance of lime for the formation of such beds would be found in the thick beds 
of limestone, or, disseminated with the sands and clays of the great mass of the strata. Whole 
beds of limestone may have been transformed from the carbonate to the sulphate. With respect 
to the sources of the sulphuric acid, its origin is indicated to us by the highly sulphurous nature 
of the water constantly being poured out on the surface of the Llano, or in the valleys of the 
streams on its borders. These waters contain much sulphuretted hydrogen in solution, which, 
on exposure to the oxygen of the air, becomes converted into sulphuric acid. These springs 
may have once been much more numerous and powerful, and may have been charged with free 
sulphuric acid. The water may either have risen to the surface, or permeated the strata from 
below. Another source of sulphuric acid may have been found there in entombed organic 
remains, which, by their decomposition, give rise to sulphuretted hydrogen. 
I am pleased to find that Mr. Dawson also regards the action of free sulphuric acid upon beds 
of limestone as the probable cause of the formation of the gypsum beds. In relation to this 
subject, he makes the following observations: “For the gypsum of hTova Scotia, occurring, as 
it does, in thick and extensive beds, interstratified with marl and limestone, there appears to 
me to be but one satisfactory theory—that of the conversion of beds of calcareous matter into 
sulphate of lime by free sulphuric acid, poured into the sea by springs or streams issuing from 
volcanic rocks. Modern volcanoes frequently give forth waters containing sulphurous and 
sulphuric acid. In the volcanic region of Java, for instance, there is a lake of sulphuric acid, 
from which flows a stream in which no animal can live. The water of this stream being, 
probably, more dense than sea-water, will naturally flow along the bottom of the sea, and, if it 
meets with beds of calcareous matter, will convert them into gypsum .” 1 
IV. LEAD. 
Lead and silver mines of the Organ mountains.—Description of the specimens.—Galena.—Cerusite. 
I find several large and fine specimens of lead ores in the collection, but they are without 
labels. In Captain Pope’s Report, however, mention is made of “ valuable silver and lead 
mines” on the west side of the Organ mountains, “extending over a continuous distance of 
twenty-five miles .” 2 He also states that specimens from these mines were obtained and 
brought in. I therefore .conclude that the specimens are from the above locality. 
As our knowledge of these mines is so limited, and every fact concerning them is of the 
1 Acadian Geology, pp. 223, 224. 2 Report of Captain Pope, p. 31. 
