AUTHORS ABSTRACTS. 
Origin cf the lowa Lead and Zine Deposits. By A. G. LEonarp. Am. 
Geol., Vol. XVI., November 1895. 
The deposits occur in the northeastern corner of the state and 
form part of a larger area embracing the southwest portion of Wiscon- 
sin and northwest corner of Illinois. The ore occurs in crevices in 
the Galena and Trenton limestones, and in Iowa most of it has been 
taken from the upper fifty feet of the Galena beds. 
The minerals were originally deposited as sulphides along with the 
sediments in certain areas where, borne by currents, they first came in 
contact with abundant organic life. There is no evidence of general 
diffusion and subsequent concentration by surface decomposition of 
rocks as apparently the case in Missouri. 
At a later period the Galena beds were raised into folds and east 
and west fissures formed which becoming channels for underground 
waters were enlarged into cave-like “openings.” In the latter the 
ores mostly occur. 
There is nothing to show that the deposits were formed by hot 
solutions rising through fissures from great depths. On the other 
hand there is abundant evidence to prove that to the process of lateral 
secretion is due the deposition of the ores in the crevices and that 
they have thus been derived from the limestone whence they have 
been leached by surface waters. There is reason to believe that the 
Galena limestone contains lead and zinc diffused through it in small 
quantities. This theory does not necessitate the derivation of the 
minerals from the rocks immediately adjacent, but they may have been 
leached for a considerable distance on either side. Thus the metallif- 
€rous contents of the country rock would be sufficient to supply the 
deposits. 
The Gold-Silver Veins of Ophir, California. By W. LinpcreN. Four- 
teenth Ann. Report of the U. S. Geol. Survey, pp. 243-284. 
The deposits described are located in the gold belt of the Sierra 
Nevada near the contact of a massif of granodiorite of late Mesozoic 
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