Revieio of Recent Geological Literature. 12S 
3. The ore is oolitic, and the oolyte has a concretionary structure, 
embracing in each lenticule, a rounded grain of quartz. 
4. The concentric layers of the lenticules consist of alternations of 
silica and hematite, which becomes evident on the removal of the latter 
by hydrochloric acid. The silica is sometimes amorphous, and some- 
times appears, under the microscope, to be chalcedony. 
5. This structure pervades the Clinton ore from Dodge county. Wis., 
from Rochester and Ontario, N. Y., from Tennessee, Georgia and Ala- 
bama; and even when the ore consists largely of the forms of Bryozoa 
such forms are permeated and coated with layers of ore, associated with 
silica, showing an intimate relation in the origination of the silica and 
the ore. 
6. The shoal waters indicated by the character of the associated 
rocks at Clinton, were favorable for the formation of iron ore by sedi- 
mentation. 
. 7. If these lenticules were originallj' of calcite they must have been al- 
tered from the exterior inwardly, but in no case has there been found 
any remaining trace of such calcite. 
8. The strata are still horizontal, and percolating waters could not so 
uniformly reach and change a limestone layer, and especially to the 
neglect of other limestones overlying, situated even more favorably for 
such change. 
9. There seems to be a false chemical assumption in presuming that 
meteoric waters already surcharged with lime carbonate will also carry 
along iron salts and receive more lime in exchange for the iron at a cer- 
tain definite stratigraphic level. 
10. The lowest layer of iron ore is separated from that above it by a 
calcareous bed of shale. The substitution hypothesis requires that 
meteoric waters should pass through this shale leaving its 5 p. c. of lime 
unaffected and depositing no iron, but should abstract all of the lime in 
the lower layer where the ore is found — which seems to be gratuitous 
play of imagination. 
11. The bottom tier contains a lean ore, but its leanness is not due to 
an excess of remaining lime, but to a greater deposit of concretionary 
and fragmental silica. "It is in fact a ferruginous sandstone." 
12. Instead of a removal of calcite by percolating waters the process 
has been the reverse and calcite is found to embrace the iron spherules 
some of which have been partially broken and exfoliated prior to such 
calcareous deposition. 
13. Wherever the spherules are found iu patches and irregular 
groups throughout the rock, though not constituting a good ore, they 
are as completely formed of iron and silica as when they constitute ore. 
If they resulted from replacement they would naturally be only partially 
changed. 
14. Oolitic iron ores are being formed at the present day in conditions 
similar to those supposed for the Clinton shores and estuaries; such 
only need dehydration, which goes on at ordinary temperatures, to re- 
semble closely the Clinton ores. 
