SUPPLEMENTAL REPORT—HANGING ROCK DISTRICT. 899 
shale, sandstone, or conglomerate, in which the remains of animal or 
vegetable life are, for the most part, wanting. The presence of any one 
of these elements proves the existence ‘of conditions favorable to life, 
but they separately mark the varying conditions of the surface upon 
which they were deposited. Coal, as has been pretty well established, 
accumulated in marshes near the sea level. Beds of fossiliferous lime- 
stone were formed upon the sea floor in warm and clear water, but no 
great depth could have been required. If the ore seams are contempor- 
~ aneous with the rocks in which we find them, they must owe their origin 
_ to conditions very similar to those under which limestones grew; but one 
theory of their origin is that they have been formed by a segregation of 
their materials from adjacent beds since the original deposit. 
When a coal. seam, then, is overlain by a fossiliferous limestone, as 
happens again and again in the series under consideration, there is clear 
proof that a subsidence of the coal swamp took place, so that its former 
area came to be occupied by clear and warm sea water. When the lime- 
stone in turn is covered by a bed of iron ore, there is perhaps indicated 
an upward movemeni of the sea flcor, by which a partial return to the 
conditions of the coal swamp was effected. The beds that intervene be- 
tween the horizons of life, and especially the great sandstone ledges that 
occupy so large a portion of every section, indicate conditions very widely 
different from those already hinted at. They show apparently a greater 
depth of water, currents of considerable force and range for the transpor 
tation of the rock material from distant sources, and, through some causes. 
a very great diminution always, and sometimes the entire absence, of the 
former life of the seas. ; 
These mutations that succeed each other so often in our scale, it tasks 
the imagination to follow and restore. 
In filling up the series of the district under review, the frame work 
already pointed out will, of course, be used. The iron ores of the series 
will first be located and briefly described, and afterwards the coal seams 
_will be treated in like manner. 
% 
B. IRON ORES OF THE HANGING ROCK DISTRICT. 
Seams of iron ore are found at a multitude of horizons in the Hanginy 
Rock District. Some of the deposits are altogether local in their occur- 
rence. Found in a single section, they may never be met again. A. 
few, however, extend through the whole field. Of the six limestones 
that constitute the main series, five are capped with iron ore, the Ames 
being the only one that is not socovered. The accessory limestones also. 
for the most part, carry ore. It is this association of ores and limestones 
“> at makes the identification of the former possible in widely separated 
