196 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [BULii.213. 
Ore associated with quartz druses.— Not infrequently, in the Ordo- 
vician dolomites, the lower ore horizons exhibit quartz druses and 
surfaces covered with minute quartz crystals. The ore in these rocks 
occurs as clean, bright crystals deposited on the quartz. It seldom is 
found in large masses, but is generally distributed through the rocks. 
The probability is that it represents a migration from the higher 
horizons, but it is possible that it was deposited from the depleted 
solutions at the time of primary deposition. 
Opinions of previous writers. — In the previous reports on the 
northern Arkansas field certain ideas have been advanced which are 
not accepted by the writer. These largely pertain to theoretical con- 
siderations, although some of them deal with the geologic facts. 
There is no opportunity in this article for a discussion of the differ- 
ences of opinion which have arisen, but it is thought best to mention 
certain points which are obvious from a review of the literature. 
The writer has argued that the bedded breccias were produced by 
the movement of strata past one another, as a result of compressive 
forces. Mi'. Branner, in speaking of the breccias, states that the 
bedded breccias were not formed on fractures, but along ancient 
underground water courses. The breccia deposits which Mr. Bain 
described were considered by him to have been formed along zones of 
pressure. He speaks of limestone conglomerates, which, in the opinion 
of the present writer, are in reality breccias. The relation of these 
so-called conglomerates to the brecciated beds, and the extensive 
brecciation due to differential horizontal movement, do not seem to 
have been recognized by Mr. Bain. 
In regard to the faulting of the region, the writer presents an inter- 
pretation which is decidedly opposed to that of Mr. Branner. lie con- 
siders certain of the most important faults, some of which were 
described and figured by Mr. Branner as thrust faults, to be normal 
faults. 
In regard to the theory of ore deposition, all the differences can not 
be here pointed out. However, Mr. Branner described bedded 
deposits contemporaneous with the rocks in which they occur. Such 
ore bodies are believed by the writer to be the result of secondary 
alteration and replacement. Mr. ]>ain has given considerable promi- 
nence to what he calls disseminated ores in compact limestone and 
unbroken conglomerate. This description does not seem to be a cor- 
rect characterization of any of the main ore bodies of the district, 
a Branner, J. C, Zinc and lead deposits of northern Arkansas: Ann. Rept. Arkansas Geol. Sur- 
vey for 1892 (published in 1900), Vol. V; also Trans. Am. Inst. Min. Engrs., Vol. XXXI, p. 572. 
Bain, H. F., Preliminary report on the lead and zinc deposits of the Ozark region: Twenty-second 
Ann. Rept. U. S. Geol. Survey, Pt. II, 1902, pp. 195-202. Van Hise, C. R., and Bain, H. F., Lead and 
zinc deposits of the Mississippi Valley, read before the Institution of Mining Engineers at the 
general meeting at London, May 29, 1902: Excerpt from Trans. Inst. Min. Engrs., pp. 34, 35. 
