Prime.} 250 [Dee. 21, 
The limestone varies from a blackish-blue to dove color, being for the 
most part compact to semi-crystalline, while there are occasionally shaly 
beds. In composition it varies much, often approaching a true dolomite, 
again a pure limestone. But from the isolated analyses made it would 
seem as if the percentage of magnesia was less in the upper beds than the 
lower ones. The limestone is always siliceous, often very much so, and 
hence much care is now being taken by many of the iron-masters in select- 
ing beds of it, as a flux in their furnaces, which are low in silica, so as to 
be suitable for smelting the iron ores of the Great Valley and New Jersey, 
which are also high in silica. It often contains minute grains of pyrite 
disseminated through it, which weather out on exposure, leaving minute 
cavities behind. Numerous analyses have shown the presence of ferrous 
carbonate varying in amount from 0.538 to 1.505 per cent. 
A peculiarity of the limestone is that itis often brecciated, the fragments 
being composed exclusively of limestone, cemented together by calcite or 
dolomite. The brecciated appearance is rarely visible on fresh fracture, 
being usually brought to view by weathering. When seen in place it will 
usually be found that one or more brecciated beds occur between two 
others which do not exhibit this peculiarity. As the beds of the No. II 
limestone have been much disturbed by the force which elevated the South 
Mountain range, the probable explanation of this brecciation is that a very 
hard, unyielding bed occurs between two more pliable ones ; that these, 
when subjected to the lateral thrust of the uprising mass of the South 
Mountains, bave conformed themselves to the folds of the strata, while the 
harder one, being unable to do this, has been fractured and re-cemunted in 
siti, by the percolation of caicareous waters. 
Some observers have supposed that the No. II formation is actually 
composed of two limestones, the lower one belonging to the Huronian, 
the upper to the Calciferous; and patches of the latter are supposed to 
overlie the former. The upper limestone (according to these observers) 
having been formed from the lower, the brecciated limestones are adduced 
as evidences of upheaval and shore action. 
The explanation I have offered of the formation of the brecciated lime- 
stone is both more in accordance with the facts observed and with the 
generally accepted view of the deep-sea formation of limestone than the 
hypothesis above stated; for the brecciated limestones are as common 
near the base of the series as the top. q 
Besides the genus Monocraterion found in the Lehigh county limestone 
belongs to the same family as Scol/thus, and is therefore no greater proof 
of age than the latter ; and it occurs in but one locality close to the top of 
No. II, having not more than fifty to one hundred feet from the overlying 
Calciferous and Trenton. 
The fossils thus far found in the No. II limestone do not number a dozen 
specimens, and have been found in but four localities. At Helfrich’s 
Spring, about two and a half miles north of Allentown, the Jordan makes 
a great bend around a limestone hill, and, by an underground passage of 
