460 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



distances of the strandline. If the bottom had declined more gently the 

 fine material would have been carried farther out by the undertow. 



The second example is the contact between typical Lowville limestone 

 and an older, probably late upper Chazy, limestone, seen at Fort Loudon, 

 Pennsylvania. The top surface of the lower bed suggests subaerial corro- 

 sion. On resubmergence 0-2 or 3 inches of calcareous clay, presumably 

 mostly surface wash, was swept into the small hollows, while the more 

 prominent parts were largely covered by fixed organisms such as Bryozoa 

 and crinoids.' The first foot or so of the succeeding deposits includes a 

 fairly representative littoral fauna, but the matrix is rather pure lime- 

 stone. 



The third is one of many similar examples observed in the Mohawk 

 Valley of New York, where the Lowville limestone is very incompletely 

 represented, and followed directly by either late Black Elver (Amsterdam 

 limestone) or early Trenton limestone. The upper surface of the Low- 

 ville is usually smooth and often pierced by small vertical worm burrows. 

 The contact with the overlying formation is very tight and as a rule 

 shows no trace of land wash material. There was probably very little of 

 this to begin with and what there was must have been quickly carried out. 

 The new precipitation, then, was laid directly on a cleanly washed floor 

 of Lowville limestone. 



The fourth example was observed in the quarries at Darlington, Wis- 

 consin. In most respects this case is like the last, and the rocks involved 

 are of similar ages. It differs, however, in that a part of the original 

 surface wash is preserved in a cavern, into which it was probably swept 

 by waves and tidal movements of the water. ( See further remarks, pages 

 364 and 466.) 



The fifth is an interesting contact between early Helderbergian lime- 

 stone and the Onondaga limestone recently observed at Manlius, New 

 York. The contact is clean and sharp and, although the surface of the 

 lower limestone was roughened by subaerial decay and Oriskany sand- 

 stone occurs near by, there is no trace of land detritus. 



The sixth example is even more surprising. It is the well known con- 

 tact between a highly inclined and eroded Ordovician sandstone forma- 

 tion and a late Silurian or early Helderbergian limestone at Rondout, 

 New York. The unexpected feature in this case is that whereas the 

 eroded edges of the sandstone layers formed a very uneven, sharply ribbed 

 surface, the succeeding limestone deposit reaches to the bottom of the 

 furrows without intervention of land detritus. Evidently, when this 

 sandstone area was submerged the advancing sea immediately proceeded 



