98 



SCIENCE. 



[N. S. Vol. II. No. 30. 



overlapping the southern extension of South 

 Mountain from Pennsylvania. Five or ten 

 miles to the east, on both sides of the Po- 

 tomac, Catoctin Mountain repeats in many 

 respects the structural and geographical 

 features of Blue Eidge and South Mountain. 

 The geographical features of this region are 

 described and explained in a valuable essay 

 on the ' Geology of the Catoctin Belt ' by 

 Arthur Keith (14th Ann. Eep., U. S. G. S., 

 1895,293-395). The Tertiary ' baselevel' 

 is the most extended surface of the region. 

 Catoctin and various other residuals of hard 

 rocks rise above it, and numerous vallej'S 

 are entrenched beneath it. Three stages of 

 post-Tertiary denudation (two Pleistocene 

 and one recent) are indicated by the ' base- 

 levels ' observable in the valleys. The even 

 summits of Catoctin and the other residuals 

 above the Tertiary plain indicate two stages 

 of pre-Tertiary denudation ; but these older 

 ' baselevels ' are now so greatly consumed 

 that they are referred only in a general way 

 to Cretaceous time. Judging by the vol- 

 ume of denuded rocks, the ratios of Ter- 

 tiary, early Pleistocene, later Pleistocene and 

 recent time are as 134, 1, f , and a ' small 

 fraction.' The small consideration of ma- 

 rine erosion marks the essay as distinctly 

 belonging to the American school. 



The residual hills of this region are so 

 characteristically developed that in 1891 

 McGee suggested the use of Catoctin as a 

 generic name for such topographic forms 

 (5th session, Internat. Geol. Congress, 249), 

 in the same way that I have used Monad- 

 nock in New England (Nat. Geogr. Mag., 

 v., 1893, 70). Eecent practical experience 

 has shown me that it is convenient to use 

 both these terms; Monadnoch to applj' to 

 residual eminences that surmount pene- 

 plains of Cretaceous denudation, such as are 

 common in the highlands of New England 

 and Carolina, and Catoctic to apply to the 

 residvials that surmount Tertiary pene- 

 plains, such as are common over the inner 



piedmont belt of Virginia. Whether so 

 special a terminology will commend itself 

 to general usage remains to be seen. It 

 may be noted tliat Keith employs ' base- 

 level ' in a topographic sense to which strong 

 objection may be urged. (See Science, 

 February 15, 1895, 175.) 



KECENT TOPOGEAPHICAL MAPS. 



Eecent topographical sheets issued by the 

 United States Geological Survey represent 

 a number of areas of particular interest. 

 Those for New York, the joint product of 

 State and National funds, are especially wel- 

 come. The Oriskany, Oneida, Chittenango 

 and Sj'racuse sheets portray the northern 

 margin of the Alleghany plateau where it 

 descends to the lowland of central New 

 York ; the eastern sheet includes Eome, 

 where the Mohawk enters the broad valley 

 that, according to Gilbert, once served as 

 the outlet of the expanded Lake Ontario. 

 The Syracuse sheet includes the beginning 

 of a remarkable area of drumloidal drift 

 hills, and also shows some of those curious 

 abandoned channels near the margin of the 

 plateau that seem to have been cut by tem- 

 porary streams, constrained into peculiar 

 courses by the melting ice sheet. Elmira 

 and Rochester are included on other sheets 

 of interest in connection with recent papers 

 of Fairchild (see Science II., p. 11.; Amer. 

 Geologist, xvi., 39-51). The Ithaca sheet 

 illustrates the general dissection of the 

 plateau and the morainic obstruction of 

 some of its valleys, referred to by Chamber- 

 lin (3d Ann. Eept. U. S. G. S., 357). The 

 Catskill and Ehinebeck sheets make the 

 series for the Hudson almost complete from 

 New York City to Albany. A large part 

 of the Ausable basin in the Adirondacks is 

 included in the Mt. Marcy, Ausable and 

 Plattsburg sheets, offering interesting prob- 

 lems about lakes and gorges for attentive 

 study. The Pulaski sheet at the eastern 

 end of Lake Ontario exliibits the simplili- 



