'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, a." 

 happens ag.-iin 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 ca,me 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 movement of the sea floor, 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 tbt: 

 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, fee used. The iron ores of the serien 

 will first be located and briefly described, and afterwards the coal seam-j 

 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 Hangin tr 

 Rock District. Some of the deposits are altogether local in their occui- 

 rence. Found iu a single section, they may never be met again. A 

 few however, extend through the whole field. Of the six limestonen 

 that constitute the main series, five are capped with iron ore, the Am( s 

 being the only one that is not so covered. The accessory limestones also 

 for the most part, carry ore. It is this association of ores and limestones 

 •' " ^t makes the identification of the former possible in widely separated 



