448 



SCIENCE 



[N. S. Vol. XXXVII. No. 951 



Here is a general statement that there is an 

 " old " and a " young " drift in the " upper 

 Alleghany region," and that a " great ero- 

 sion " occurred between their deposition. The 

 generality of the statement would lead one to 

 infer that the erosion was general throughout 

 the region, and that this fact was generally 

 received, as well as that there was such a dis- 

 tinction between the " old " and " young " 

 drifts that they could be readily differentiated 

 everywhere by physical characteristics. 



In discussing this statement we must first 

 ascertain what Mr. Leverett considers " the 

 upper Alleghany region," as the river is a 

 long one. Happily we have in the map com- 

 piled by Mr. Alden for the Geological Survey 

 a very plain demarkation of areas variously 

 estimated by Mr. Leverett. In the above dis- 

 cussion he uses the term " old " drift, refer- 

 ring to the first or Kansan advance. Com- 

 bining this statement with the areas of the 

 map we arrive at the conclusion that the 

 uppermost portions of the Alleghany region 

 to which he can possibly refer begin in the 

 immediate vicinity of Warren, Pennsylvania, 

 which is about 100 miles from the source of 

 the river, as above that place the river is 

 marked as flowing through areas not reached 

 by Kansan ice. The terms Kansan and Wis- 

 consin are used to define alleged earlier and 

 later phases of glaciation separated by a long 

 interval. We will, therefore, discuss the con- 

 ditions of this system from Warren southward ; 

 but as there is no method of estimating where 

 Mr. Leverett's term " upper " ends, we will 

 continue our discussion to and below Parker, 

 which is half way between Warren and Pitts- 

 burgh. 



After Lewis and Wright published the vol- 

 ume of the Second Geological Survey of 

 Pennsylvania delimiting the " terminal mo- 

 raine," Carll, in his report of the Warren 

 region, called attention about thirty-five years 

 ago to the preglacial channel of the Cone- 

 wango now deeply buried throughout in drift 

 which rose near Kane and flowed westward 

 through Shefiield, Clarendon, Stoneham and 

 Glade, between which place and Warren it 

 crossed the present channel of the Alleghany 



and flowed north into the St. Lawrence drain- 

 age system. On the northern bank of this 

 stream and over 100 feet above its present 

 level is a remnant of Mr. Leverett's " old 

 drift." Between the time of its deposition 

 and the excavation of the wide valley to 

 present level he imagines that a long period 

 has elapsed, and this excavation is his " great 

 erosion." At Clarendon is more of his " old 

 drift," also at Franklin; also at Parker. 

 Bradford, being above Warren, is in the un- 

 glaciated area. The distances apart of these 

 places are: Bradford to Warren (along the 

 valley lines), 60 miles; Warren to Franklin, 

 60 miles; Franklin to Parker, 35 miles; Kit- 

 tanning is about 25 miles below Parker. 

 These distances enable us to employ the rule 

 which obtains in geology as well as geometry, 

 that when a number of points in a line or 

 plane sufficiently distant from one another 

 have been referred to a given datum plane, 

 the portion of the line or plane included be- 

 tween those points has also been referred to 

 the same plane. The datum plane in this case 

 is the present drainage level of the Alleghany, 

 and to it we will refer both the underlying 

 rock bottom and the " old drift " of Mr. 

 Leverett. 



Our data for reference exist abundantly, as 

 the region had been pierced from surface to 

 great depths by tens of thousands of oil wells 

 whose sections have been recorded, and many 

 have been published. These wells are found 

 in numbers on the " old drift," the " young 

 drift," the mountain tops, the swamps and 

 the river beds, and where rock was not near 

 the surface a pipe was driven through the 

 loose deposits till rock was struck. These 

 " drive-pipe " records show the materials 

 passed through, and form a valuable and con- 

 clusive array of facts beyond the possibility 

 of cavil or argument. 



The problem for discussion is the probable 

 form and sequence of deposits over a region 

 deeply flooded by an approaching but still dis- 

 tant glacier which forced the waters over a 

 still more distant col which was gradually 

 degraded. Every prospector and ore-dresser 

 is well acquainted with the classifying and 



