October 27, 1905.] 



SCIENCE. 



531 



formed anywhere under favorable conditions. 

 But we do not generally apply this principle 

 in the elucidation of our rock sections. When, 

 for example, a prolonged subsidence of the 

 land occurs, resulting in the overflow of the 

 land by the sea, the waves of .the advancing 

 sea will work over the residual soil of the 

 land which it overflows and will spread a 

 basal layer of conglomerate or sand or, in rare 

 cases, of mud over the old land thus sub- 

 merged, the nature of the basal bed depending 

 on the character of the rock debris which 

 covered the old land, the slope of this old 

 land and the consequent depth of the en- 

 croaching sea, and the rapidity of the sub- 

 mergence. This latter may be so great that 

 areas of land are suddenly submerged, while 

 the shore is transferred far up on to the old 

 land, so that ofl'shore deposits, like organic 

 limestones, may form directly on the old land 

 surface. 



The basal layer thus formed will not be of 

 the same age throughout, but will rise in the 

 scale with the advance of the sea. Seaward, 

 finer deposits will be laid down upon the basal 

 formations, these finer deposits corresponding 

 in age to the basal sandstone at that time 

 forming near the shore. To illustrate : the 

 basal sands of the Cambric Ocean were spread 

 by an advancing sea over the crystalline rock 

 floor. East of Lake Champlain this basal 

 sandstone belongs to the Lower Cambric, but 

 westward it rises in the scale until at the foot 

 of the Adirondacks it is the Potsdam sand- 

 stone of Upper Cambric age, while the corre- 

 sponding deposits further east are clay and 

 lime-rocks. Again, while on the east of the 

 Adirondacks, at the point of present outcrops, 

 the basal sandstone is Potsdam, followed by eal- 

 ciferous sand-rock and by purer calcarenytes 

 of Beekmantown age, the outcrop on the west 

 of the Adirondacks shows similar basal quartz 

 sandstones, followed by calciferous sand-rock 

 and later by pure calcilutytes, but all, from 

 the base vip, of Lowville or Upper Chazy age. 

 The Beekmantown and Potsdam are here over- 

 lapped by the later deposits, which, however, 

 repeat the lithic sequence seen in the section 

 of earlier age on the east of the Adirondacks. 

 Wells sunk in the neighborhood of Syracuse 



to the crystalline rock, find a quartz sand- 

 rock (silicarenyte) resting immediately on the 

 crystalline, followed by a calciferous sand 

 rock (calcareous silicarenyte), which grades up 

 into siliceous calcarenyte, and finally into pure 

 calcarenytes or clastic limestones. Lithically 

 considered, this section might be regarded as 

 representing the whole series from Potsdam 

 up, whereas in reality the basal bed is Beek- 

 mantown, if not Upper Chazy. 



Regressive movements of the sea, by which 

 large tracts of previously submerged land be- 

 come exposed, also leave a record in the sedi- 

 mentary series which, by careful consideration, 

 can be detected. Thus a comparison of sec- 

 tions shows that we have in the Mohawk Val- 

 ley some three or four hundred feet of Beek- 

 mantown, which in places, as at Little Falls, 

 rests directly upon the gneiss with a basal 

 rudyte. These Beekmantown beds probably 

 represent the lower, though probably not the 

 lowest, members of that formation, judging 

 from the presence of Opheleta complanata. 

 Not more than a hundred and fifty miles 

 south, in central Pennsylvania, the Bee]s;man- 

 town is represented by over two thousand feet 

 of similar strata, followed by some two to 

 three thousand feet of the Stone's River group, 

 which in the Mohawk is represented by less 

 than a hundred feet of its upper portion, and 

 there known as Lowville. Similarly, in the 

 upper Mississippi region the Lower Magnesian 

 limestones, which indicate a continuous de- 

 position from the Upper Cambric, are less 

 than three hundred feet in thickness and rep- 

 resent the lowest Beekmantown. The Stone's 

 River, or Chazy, is represented by less than 

 a hundred feet of strata, which grade upward 

 into the Black River, as do the corresponding 

 strata — Lowville — in the Mohawk and Black 

 River Valleys. These Stone's River beds of 

 Minnesota, from their relation to the overlying 

 beds, and from their fossils, are seen to be the 

 uppermost portion of that series. Between 

 the lowest Beekmantown and the highest 

 Chazy (or Stone's River) lie about 200 feet 

 of pure quartz sandstone — a typical sili- 

 carenyte— known as the St. Peter sandstone. 

 This sandstone has been traced very widely 

 over the Mississippi Valley region; but as 



