Lesley.] ^'JQ [December. 



the lowest sandy layers of the limestone, gives us likewise a second 

 great belt of iron ore deposits, lying along the foot and part way up 

 the side of the South Mountain. These are the deposits of which 

 Professor Hitchcock speaks in Vermont ; and in one of these in 

 Pennsylvania, viz., in the Pond-bank of Mont Alto Furnace, the 

 lignite has been found. 



Along the foot of the South Mountain, the feebler brooks, de- 

 scending from the ravines, sink immediately beneath the surface into 

 a system of underground caverns, which may, without much exag- 

 geration, be called a single cave, extending for a thousand miles, and 

 including in its course chambers, some of which, like Weir's Cave, in 

 Virginia, have become celebrated among the wonders of the world. 

 The stronger bi'ooks unite, and form large streams, or even rivers, 

 which, — like the Lehigh below Allentown, the Yellow Breeches west 

 of the Susquehanna, the Shenandoah south of the Potomac, — flow 

 close over the southern or lower edge of the limestone formation, 

 and therefore close up to the foot of the mountain. 



Both this situation of the river drainage on the surface, and this 

 cavern system underneath, tell one story, which cannot be misinter- 

 preted, — the extra dissoluhility of this particular horizon of Lower 

 Silurian rocks. And that, which we now see going on before our 

 eyes, has, of course, been going on for ages. The fissures which are 

 now being enlarged into caves, and the caves which are fast growing 

 into catacombs, and ramifying into labyrinths of underground dark- 

 ness, their roofs every now and then falling, so as to produce funnel- 

 shaped sinkholes in the fields and sometimes in the roads, and their 

 floors receiving, through the sinkholes, lots of leaves and fruit, 

 land shells, and perhaps occasionally bones of smaller animals, with 

 every great spring freshet, — all these once had their analogues in 

 time past (vanished now into thin air) beneath some old surface, 

 situated many feet or yards, in fact many fathoms, above the one 

 on which men live to-day. 



By this ideal reconstruction of surfaces older and above the pre- 

 sent one, we settle most of the difiiculties which encounter us in 

 studying the ores of the Great Valley. And I submit, that we ob- 

 tain, also, a reasonable explanation of the sporadic masses of lignite, 

 two of which are now known to exist in or rather near the iron ore; 

 for it must not be forgotten that the lignite and ore are not in con- 

 tact at either place. It is only necessary to suppose a sink hole so 

 formed, and so stopped up below, as first to receive and then to re- 

 tain an accumulation of forest trash, and we have the thing ready 



