260 The Amei'tcan Geologist. October, is'.tv 
inches to eight feet in thickness, three of them having over four feet of 
good coal, api)anMitly a free-l)uruing bitumiaous variety, resembling that 
of the Cape lireton mines. 
^1 propoKed Ki/artii of chronologic curtnyraphy on n phyxiogriiphic hit»in. 
By President T. C. Chamberlin. With The. geological dates of origin of 
certain topographic fornix on the Atlantic dope of the United Htaten. 'Ry 
William Mourns Davis. Bulletin, G. S. A., vol. ii, pp. 541-544, and 545- 
586, with six figures in the te.\t; July 2, 1891. Increasing attention has 
been given during recent years to topographic forms as time indices and 
means of geologic correlation. President Chamberlin therefore pro- 
poses a cartograjihic system, in which plains shall be represented by 
lines, and slopes b}^ dotted surfaces, both to be put on in colors varying 
according to the geologic date of these topographic forms. The direc- 
tion of the agency by which they were produced may also be shown. 
Thus, a riuvial plain will be indicated by arrows (without feathers) 
pointing in the direction of the current, while a lacustral plain will be 
mapped by parallel lines headed with arrows-points ou the margin shore 
erosion by waves having been the most characteristic agency in its pro- 
duction. In the case of subaerial plains or peneplains, parallel lines 
will be used without arrow-heads. To distinguish between a plain and 
a peneplain, which maj^ be (juite rolling and yet clearl}' determinable, 
continuous lines may be used for the former and broken lines for the 
latter. 
Professor Davis recognizes a Cretaceous peneplain in southern New 
England, Xew York, New .Jersey, and southward, into which the rivers 
of the Atlantic slope have cut broad and deep valleys during the 
Tertiary era. The Hudson river, for examjile, is shown to have excavated 
the whole gap between the Catskill and Berkshire plateaus since tiie 
early Tertiary uplifting of this peneplain. The level crests of the- 
Appalachain ranges are remnants of the Cretaceous base-level, into which 
streams have channeled the great interveniag valleys during Tertiary 
and Quaternary time ; but the White mountains of New Hampshire and 
the Black mountains of North Carolina have existed, constantly under- 
going denudation, from much earlier dates. 
Variations in the Cretaceoun and Tertiary strata <f Alahamii. By 
D.\NiEL W. LAN(iDON, Jr. Bulletin, G. S. A , vol. ii, pp, 587-60(5, with 
one plate : July 8, 1891. This paper presents detailed descriptions and 
sections observed during the boat journeys down the Tombigbee, Tusca- 
loosa, and Alabama rivers, with which the sections exposed farther east 
by the Conecuh, Pea, and Chattahoochee rivers are compared. Special 
attention is directed to variations in the strata on account of different 
conditions of sedimentation.to faunal changes,and to unconformities due 
to the total absence eastward of formations that are well defined in the 
western part of the state. On the Tombigbee the Cretaceous beds measure 
about 2,560 feet in thickness, and the Eocene about 1,655 feet ; while ou 
the Chattahoochee these are reduced respectively to about 1,440 and 
1,145 feet. 
