DOLOMIZATION. ale 
time. The dolomite often incloses small grains of pyrite, or is stained by 
disseminated limonite. 
A peculiar structural feature which evidences the secondary origin of 
the dolomite, both that in the extensive beds and that of the later period, is 
the prevalence of many closely set jomts, which characterize the rock in its 
fresh condition. Furthermore, most of the dolomite belonging to the later 
period seems to have formed in the vicinity of watercourses, and since its 
formation it has been peculiarly liable to oxidation from surface waters, 
which have flowed continually along these courses, even up to the present 
time. The result of this has been the alteration of a certain amount of 
carbonate in the rock, with possibly the removal of some carbonate in 
solution. This has brought about a marked reduction in bulk, so that this 
dolomite is always very close jointed, or, as called by the miners, “short.” 
A part of the carbonate in the fresh dolomite is iron carbonate, and on 
oxidation the yellow limonite resulting from this stains the rock, thus 
giving rise to the name “brown lime,” by which, also, the dolomite is 
known at Aspen. 
AGENTS OF DOLOMIZATION. 
From the distribution of the dolomite belonging to the later epoch 
along the fault zones and other channels where water has for a long time 
circulated freely, it is evident that waters have been the agents of change. 
It may now be well to inquire what was the nature of this circulating 
water. Harkness, who has been quoted as describing similar dolomiza- 
tion along joints in limestone near Cork, in Ireland, attributes the change 
to sea water which penetrated downward along these channels. Bischof? 
mentions dolomite as accompanying ore deposits in limestone in France, 
and Adolph Schmidt” also finds that in the large lead and zine deposits of 
Missouri the limestone has been dolomized along fissures and in the neigh- 
borhood of the ores. Both these latter writers refer the change to the 
action of solutions of magnesium bicarbonate. 
Leaving out of the question the chemical changes which the waters 
that circulated along these faults and fractures have wrought in the rock, 
their more ordinary effects are strikingly like those of the water which still 
circulates through these channels at the present day. From the Castle 
Chemical and Physical Geology, English translation, London, 1859, p. 179. 
* Trans. St. Louis Academy, 1875. 
