532 



SCIENCE. 



[N. S. Vol. XXII. No. 565. 



we follow it southward the thickness of 

 Beekmantown below and Chazy above in- 

 creases more or less regularly, until in In- 

 dian Territory, where the St. Peter thins 

 away, we have nearly two thousand feet 

 of the Beekmantown and more than that of 

 the Chazy or Stone's River. These facts 

 point to a very remarkable episode in North 

 American Ordovicic history, namely, the slow 

 retreat of the sea from the upper Mississippi 

 Valley, which as it retreated gradually washed 

 the sands of the northern shore seaward, 

 spreading them over the previously deposited 

 offshore beds. As the sea retreated, deposition 

 came, of course, to an end. Thus when the 

 retreat had reached southern Minnesota, only 

 the lower 250 feet of Beekmantown had been 

 deposited, and there deposition stopped. When 

 the retreating seashore had reached central 

 United States, only the lower thousand feet 

 of Beekmantown had been deposited, and only 

 in southern United States, which was not laid 

 bare, was there a complete deposition of the 

 calcarenytes and organic limestones of the 

 Beekmantown. /The area uncovered — «the 

 whole of central United States — was spread 

 over by the sand left by the retreating sea, 

 and this was no doubt blown about by the 

 wind, the grains rounded and the remarkable 

 structure and purity of the St. Peter — ^probably 

 the best example of an ancient desert rock 

 extant — was thus produced. When the sea 

 again advanced over this desert area, the 

 upper portion of these sands was worked over 

 and became true water-laid deposits, and at 

 the same time graded up into the overlying 

 calcareous beds. By the time the sea had 

 advanced half way to the old northern shore, 

 a thousand feet, more or less, of the lower 

 Chazy had been deposited in the southern 

 states. At the point then reached Chazy 

 deposition began with the middle members of 

 the formation. By the time the sea had 

 reached its northern shore, from which it orig- 

 inally retreated, and which was somewhere 

 north of Lake Superior — the whole of the 

 Chazy — nearly 2,000 feet had been deposited 

 in, the southern states, the upper thousand in 

 the central states, but only the uppermost 50 

 or 75 feet in southern Minnesota. The St. 



Peter, thus representing a retreatal sandstone, 

 worked over by the winds, also represents a 

 basal bed of an advancing sea; and while the 

 last remnants of it in southern United States 

 mark practically no break in the sedimentary 

 series, this same rock in southern Minnesota 

 occupies the interval between all but the lowest 

 Beekmantown and all but the highest Chazy.^ 



Now, in New York state we have no St. 

 Peter, but we have the other conditions pre- 

 cisely like those of the upper Mississippi Va:l- 

 ley. The lowest Beekmantown is followed 

 by the highest Chazy, the interval unrepre- 

 sented between the two being marked in cen- 

 tral Pennsylvania by over 4,000 feet of sedi- 

 ment. This break, or stratigraphic uncon- 

 formity, long suspected, has recently been ac- 

 tually located in the Mohawk Valley by Pro- 

 fessor Cushing. It should be remarked that 

 during all the time that central and western 

 New York was dry land, i. e., during the time 

 occupied by the formation of 4,000 feet of 

 limestone strata elsewhere, continuous or 

 nearly continuous deposition went on in what 

 is now the Champlain Valley. 



We must now consider a somewhat more 

 complicated series. In western New York the 

 Lorraine beds — considered the highest of the 

 Ordovicic — are followed by red lutytes and 

 arenytes (mud-rocks and sand-rocks), over a 

 thousand feet thick, and unfossiliferous. At 

 the base is a quartz sandstone, about 75 feet 

 thick, and over it are about a hundred feet of 

 quartz sandstones, mostly red, and some shales 

 which contain marine fossils closely allying 

 them to the overlying Clinton. I speak, of 

 course, of the Medina formation. A little 

 south of Utica, the Lorraine shales, repre- 

 sented only by their lower hundred feet, are 

 succeeded by the Oneida conglomerate, a pure 

 quartz-pebble conglomerate with well-rounded 

 pebbles. This conglomerate, less than 50 feet 

 thick, is followed by the shales, sand, mud 

 and lime rocks of the Clinton. The base of 

 the conglomerate is fossiliferous, the fossil — 

 Arthophycus harlani — being the same which 

 is restricted to the top beds of the Medina in 

 western New York. In the cement region of 



^ Dr. C. P. Berkey will shortly publish a de- 

 tailed discussion of the St. Peter problem. 



