28 GEOLOGICAL KEPORT. ^"50, 51 



them the fragments and detritus of the older formations. Both formations 

 immediately underlie the Bluff- or Loess formation. 



Whether or not the Orange Hand deposits contain any materials necessarily 

 derived from a high northern latitude, still remains to be determined, for thus 

 far, the materials for comparison are imperfect on both sides. By far the greater 

 mass of the pebbles occurring in Mississippi appear to be referable to sources 

 lying S. of the Ohio river, on either side of the Mississippi, while the rocks most 

 common in the drift of Illinois — granite, mica-schist and metamorphic sand- 

 stone, are either very rare or (like granite) entirely wanting. It will be inter- 

 esting to inquire, whether or not the rocks composing the pebble-beds further 

 north, in Tennessee, Kentucky, Arkansas and Missouri, are derived from local- 

 ities correspondingly remote in that direction. It must be rememlered, 

 however, that the present outcrops of these formations may not nearly represent 

 the localities of the broken-doion strata which furnished the rocks, especially when 

 the dips are slight, as is generally the case in the southern portion of the more 

 immediate valley of the Mississippi. 



50. Whib therefore the materials composing the Orange Sand formation may 

 be far from identical with those found in the Northern Drift, we may neverthe- 

 less suppose the two formations to have been nearly or quite contemporaneous, 

 and caused b} ? the same flood of ice-water, which in its course denuded the older 

 strata, carrying their materials southward from their original place. Whether 

 the large angular boulders, of which a few have been found in Mississippi, can 

 be supposed to owe their transportation to some erratic ice-floe of unusual 

 thickness, may be an open question, at least until the region intervening 

 between the characteristic Orange Sand and Northern Drift (in Missouri for 

 instance) shall have received a detailed examination. 



Even at the present time, however, in severe winters, ice-floes are seen in the 

 Mississippi River below Vicksburg, and there seems to be no valid objection to 

 the supposition that the same might have happened during the drift period, 

 even if the climate should have been warmer ; since the enormous thickness of 

 arctic ice-floes would readily carry them a few degrees further south than could 

 be expected of the winter ice of the Mississippi River. 



51. The relations mentioned by Tuomey (Second Report on the Geology of 

 Alabama, p. 146) as existing between the shore of the tertiary sea and the 

 region of occurrence of the southern drift on the Atlantic slope, are not so 

 clearly recognizable in Mississippi and Alabama — owing perhaps to the slight 

 development of the later marine tertiary, and the proximity to the great outlets 

 of the continental waters. Not only do the deposits of the latter hide, to a 

 great extent, those immediately preceding the drift period, but the latter may 

 have been partially removed and destroyed by the denudations accompanying 

 that epoch. Elevated ridges of deposits unequivocally belonging to the Orange 

 Sand formation extend to within a few miles of the Gulf Coast in several 

 instances ; although more frequently, these ridges are subterranean at the present 

 time, the valleys between them being filled with sands exhibiting the lines of 



