158 Kimball — Siderite-basins of Hudson River Epoch. 



These show a greatly expanded but variable thickness as 

 well as an increased variety in the composition of the sedi- 

 ments, all of which are transitional, that is, both calcareous 

 and ferriferous. The same belt is brought to the surface 

 farther east by bosses and anticlinals, in one case reversed. A 

 line of low bluffs has been sculptured from the same range of 

 elevations 114 miles east of Mt. Thomas. The local sections 

 referred to, compassing near 1300 feet of strata, including the 

 siderite basins, may be concisely presented as follows : 



Maximum thickness. 

 Dense fissile slate at base of Taeonic hills. Probable equivalent of 



metamorphic (hydro-mica) slates further east. Weathering white. +200 ft. 



Brecciated f er ro-ealcareous sandstone 161 



Ferro-calcareous sandstones, passing into conglomerate 120 



Aphanitic black argillyte, intercalated with arenaceous shale 50 



Ferro-calcareous grits, seamed with calcite 48 



Siderite: clay-ironstone, passing into sub-crystalline spathic carbonate 44 

 Gray argillyte, weathering into drab shale. Bluffs of east bank of 



Hudson River. Boring No. 1 +662 



The grits capping the ore basins merge into thin-bedded 

 limestone in the intervals between the basins, as well shown on 

 the line of their axes along a stretch of low bluffs continuous 

 with the Mt. Thomas and Cedar Hill ore-escarpments. The 

 contact of the limestone with the underlying shales or floor of the 

 ore-basins, is in these intervals close and barren. The contact, 

 similarly exhibited in the second or eastern range of exposed 

 bosses and anticlinals, is likewise close and barren, but the cal- 

 careous grits still prevail instead of thin-bedded limestone, as if 

 the marine currents intermittently supplying the coarser grits 

 had an easterly course. Overlying grits and limestone the mem- 

 bers are of the character of hydrous fissile slates. These form the 

 surface east of the monoclinals which elevate the ore-basins, their 

 first appearance east of the Hudson being at the base of the first 

 range of monoclinal hills. These slates, probably representing 

 the hydro -mica slates of the metamorphic area to the east are 

 very persistent, especially in the foot-hills of the Taeonic 

 mountains where their great massiveness may be partially due 

 to replication, reverse dips or overthrown anticlinals occurring 

 even west of Johnstown, as shown by inferior strata. 



The correlations of this fragment of Lower Silurian geology 

 are distinctly with the same field of structural and stratigraph- 

 ical work described by Prof. Dana in the memoir already 

 cited. The series of strata here described are probably all of 

 the Hudson River epoch, and little altered by metamorphism, 

 though on the western border of the Taeonic area. 



The ore-basins themselves are not without remarkable char- 

 acteristics. They may be described as a series of beds of 

 clav-ironstone intercalated with mechanical sediments, all 



