AI^I^IVEESAIIY ADDRESS OF THE PRESIDEXT. XClll 



the great belt of iron-ore or haematite which extends along the great 

 valley for many hundred miles in Pennsylvania and Virginia ; but 

 he is anxious to show that the Lignite and the iron-ore are neither 

 of the same age nor possessed of any structural attribute common to 

 both. 



Mr. Lesley considers that it is the extreme rarity of these Lignite 

 apparitions in one of the most wonderfully continuous, extensive, and 

 valuable ore-belts of the world that gives them all their importance ; 

 and, notwithstanding the contrary assertions of Dr. Hitchcock, he 

 maintains the importance of carefully separating these sporadic 

 occurrences of Lignite from the general occurrence of the iron- ore. 



In describing the principal features of the great ore-belt of the 

 Atlantic States along the Great (Lower Silurian) Valley, which 

 begins in Canada and ends in Alabama, he shows that it belongs 

 geologically to the Lower Silurian limestone formation. It consists, 

 however, of two parts — the one stratified as the Silurian limestones 

 themselves, the other as a surface -wash over the basset edge of the 

 first. The date of this latter may be Tertiary, or even later. The 

 stratified portions must be of Lower Silurian age; but the meta- 

 morphism which they have undergone in situ, productive of stratified 

 clays and ores, may date from any time subsequent to the formation 

 of a surface-topography approximately identical with that which now 

 exists. The actual change of the original Lower Silurian calcoferrife- 

 rous sandstones and slates in situ into limonite-clay beds in ipso situ, 

 stratified as before, but charged witli an additional percentage of the ox- 

 ides from a former higher surface now eroded, and with this extra charge 

 of iron and manganese carried by percolation down to, and crystallized 

 against, their foot rock, may have required an immense time for its 

 completion, and was no doubt going on pari passu with the degra- 

 dation of the surface by slow erosion from higher to lower levels. 

 He then shows that this long era of iron- ore concentration in the 

 Lower Silurian slates could not have commenced until after the close 

 of the coal-era, and probably at a much later period. 



The author then describes the exact geological position of the two 

 great belts of iron deposit, the one at the point of contact between 

 the Lower Silurian limestone and the overlying slate-formation, for- 

 merly a deposit of ferruginous mud ; the second between the under- 

 lying slate and the lowest sandy layers of the limestone, lying along 

 the foot and part way \ip the side of the south mountain. In one of 

 these deposits in Pennsylvania the lignite has been found. 



He then alludes to the system of underground caverns, which may, 

 without much exaggeration, be called a single cave, extending for a 

 thousand miles and including chambers, some of which, like Weir's 

 Cave, have acquired a world-wide celebrity. Many of the brooks 

 descending from the mountain-sides sink into these caverns. The 

 river drainage on the surface and the cavern system below tell one 

 story, namely, ^Ae eoatra dissoluhility of this jparticular horizon of Lower 

 Silurian rocks. The fissures which are now being enlarged into 

 caves, and the caves which are fast growing into catacombs, their 

 roofs every now and then falling so as to produce funnel-shaped sink- 



