Febeuaey 11, 1898.] 



SCIENCE. 



203; 



septum, serving to support the latter and 

 also to support the oviducts. 



G. H. Paekee, 

 Haevaed Univeesity. Secretary. 



(^To he concluded.') 



CUBRENT NOTES ON PHYSIOGRAPHY. 

 DRAINAGE OF SOUTHERN OHIO. 



The greater part of the Allegheny plateau 

 and its westward slope is drained by 

 streams of the simplest kind, dissecting 

 horizontal strata in irregularly branching 

 valleys. But for some years aberrant val- 

 ley forms have been recognized in the upper 

 Ohio region, special attention having been 

 given to their meaning by W. G. Tight 

 in his latest article on ' Some preglacial 

 drainage features of southern Ohio ' (Bull. 

 Scient. Lab. Denison Univ., IX., 1897, 22- 

 32) . Confirmation is given to earlier views as 

 to the composite origin of the modern Ohio. 

 The preglacial drainage of the region led the 

 Kanawha (via Teazes Valley), Big Sandy 

 and other streams northward, across the 

 present Ohio Valley, to a common trunk 

 near Waverly. By some process not speci- 

 fied, the Ohio was given a course across the 

 middle of this earlier system, deepening the 

 older valleys for part of the distance, and 

 elsewhere trenching across the divides at 

 the lowest cols. The trenched cols, where 

 the Ohio Valley is narrow and steep-walled, 

 occur below Vanceburg, just above Ports- 

 mouth and above Guyandotte. Leverett 

 appends a brief account of his contribution 

 to this problem (1. c, 18-21). 



THE COASTAL PLAIN OF MEXICO. 



■ Studies by J. W. Spencer ( ' Great changes 

 of level in Mexico and the inter- oceanic con- 

 nections ; ' Bull. Geol. Soc. Amer., IX., 1897, 

 13-34) give, among other matters, an ac- 

 count of the coastal plain, or tierra caliente, 

 that fronts the Mexican plateaus on the 

 Gulf side. It has a breadth of fifty miles 

 back of Vera Cruz, reaching an elevation of 



1,560 feet at the inner margin, where the 

 plateau ascends boldly thousands of feet 

 above it. The inclined surface of the plain 

 has not a uniform rise, but is made up of a 

 number of steps or terraces, 50 to 100 feet 

 high, with sloping plains between them. 

 Streams descend from the plateau in val- 

 leys having a succession of reaches and 

 falls ; the same streams trench their way 

 across the coastal plain. A brief account 

 is given of the ' Geological Canal of Chivela,' 

 on the divide of the Isthmus of Tehuantepec, 

 776 feet above the sea ; its floor having 

 lately been swept over the ocean currents 

 during a depressed attitude of the region. 



MOUNTAIN STRUCTURES OF PENNSYLVANIA. 



The prevalent belief in the frequent oc- 

 currence of synclinal ridges in denuded 

 mountain ranges is discussed by A. P. Chit- 

 tenden (Bull. Amer. Geogr. Soc, XXIX., 

 1897, 175-180), who cites the opinions of a 

 number of authors on the matter. After 

 showing that there is no logical reason to 

 expect the more frequent occurrence of 

 synclinal than of anticlinal ridges in 

 ancient, deeply dissected mountains, the 

 Appalachian ridges of Pennsylvania are 

 classified and measured in three groups, 

 monoclinal, anticlinal and synclinal ; the 

 total lengths for each group being 1,333, 

 334 and 245 miles. Synclinal ridges are, 

 therefore, exceptional; the length of the 

 monoclinal ridges far exceeding that of the 

 other two classes. Synclinal ridges of 

 Pottsville conglomerate in the aathracite 

 coal regions are relatively more common 

 than elsewhere, but even there the mono- 

 clinal ridge prevails. The synclinal valley 

 between two neighboring monoclinal ridges 

 often has a high-level floor, but it is sur- 

 mounted and enclosed so distinctly by two 

 ridges that the three forms cannot properly 

 be described as a single synclinal mountain.. 



YOUNG, MATURE AND OLD LAND FORMS. 



The use of age-terms suggestive of sys- 



