Or, 
Prime. } 254. ; [Dee. 21, 1877. 
find the ore often passing through the slate or clay obliquely and intersect- 
ing the bedding. It is more probable that the ore was conveyed to its 
present position by infiltration subsequent to the formation of the hydro- 
mica slates. Whence was it derived? I have already stated that the lime- 
stone contains varying proportion of ferrous carbonate and of pyrite and 
when we consider the enormous erosion which the limestone has under- 
gone, the wonder is not that the deposits of iron ore should be so great, 
but rather that they should be so small. The ferrous carbonate and the 
pyrite oxidised to ferrous sulphate being both soluble in water, the 
former when the water contained carbon di-oxide, the waters would 
naturally carry these salts in solution until they came in contact with 
precipitating agents such as the alkaline silicates which the hydromica 
slates carry. These last became converted to carbonates and sulphates, 
leaving the iron behind, either directly as hydrated ferric oxide, or possi- 
bly as ferrous silicates which became later decomposed by the action 
of erated water to hydrated ferric oxide and free silica, which latter we 
now find so universally associated with the brown hematites as quartz. 
Whatever the origin of these ores may have been, one thing is evident, 
viz., that there is some genetic relation between the brown hematites and 
the hydromica slates, as evidenced by the almost universal occurrence of 
the ore in the slate, extending all the way from Vermont to East Tennessee 
through the Great Valley as well as in the interior valleys of Pennsylvania 
where the No. If limestones occur. 
It is well here to emphasize the fact that these brown hematite ores all 
belong to the Lower Silurian limestone formation, since, in. 1875, Dr. 
Sterry Hunt after a cursory examination of Ziegler’s Mine in Berks County, 
situated at the junction of the No. II limestone and the No. III slates, made 
the mistake, in a paper on ‘‘ The Decay of Crystalline Rocks’’ before the 
National Academy of Science, of supposing that the hydromica slates be- 
longed to the Huronian Period. A mistake into which so eminent an 
observer as himself would never have fallen had he been better acquainted 
with the region. 
At intervals along the junction of the limestones and slates there occurs 
a black carbonaceous shale, often decomposed to black or dark blue clay, 
which I have supposed to be the representative of the Utica shales. It 
consists of a very carbonaceous hydromica slate (containing damourite), 
without any fossils and may not belong to the Utica Period at all. In no 
instance has it been found more than one to twelve feet thick, but it some- 
times carries pyrite from which a portion of the iron ores, just mentioned, 
may have been derived. ‘These shales are of no economic importance. 
Overlying these come the No. III, Hudson River or Matinal Slates, 
which extend into the Kittatinny Mountains. A large portion of these 
slates are extremely useful for roofing and other household purposes, and 
extensive quarries have been opened at various points for the purpose of 
extracting them, as, however, they have been but very slightly examined, 
during the progress of the present Geological Survey of the State, I shall 
defer a more detailed description of them to some future time. 
