March 29, 1907] 



SCIENCE 



509 



duced to local peneplains of a second genera- 

 tion. The southern coast is less bold than the 

 northern, because the peneplain slopes gently 

 southward under the sea. A recent gain of 

 the sea on the land has drowned the distal 

 parts of all the streams, and carried vigorous 

 tidal currents into the incised meandering 

 valleys. Along the southern part of the shore 

 line thus determined, the sea has already 

 formed numerous smooth-beached sand reefs; 

 l)ut little advance to such maturity is seen on 

 ithe ragged western promontories and bold 

 northern coast, where marine action is still 

 chiefly destructive. 



It is gratifying to see so systematic a treat- 

 anent of a physiographic province on the basis 

 •©f structure of rock masses, process of sculp- 

 ture and stage of development, stated in the 

 eompact terms of the cycle of erosion and 

 illustrated with typical block diagrams which 

 combine structure and form in so simple and 

 suggestive a manner. It is at the same time 

 Indicative of the stage of physiographic 

 (development of the readers of the Annates de 

 Geographie — the most scholarly geographical 

 periodical in France — to note that the trans- 

 formation of valleys into arms of the sea by 

 drowning is here presented in a more or less 

 argumentative manner, as if it still needed 

 ■discussion and demonstration before it could 

 igain acceptance. It is also significant that 

 Brittany is here described as having an Ap- 

 palachian structure and development, as if 

 this new world example of a corrugated struc- 

 ture, peneplained, elevated and redissected, 

 were so well established that it served as a 

 type for the description of a somewhat similar 

 example in the old world. 



There are two points on which supplement 

 may be made to de Martonne's very readable 

 article. First, that although the sea works 

 furiously, with heavy storms and strong tidal 

 .currents, on the western and northern coast, 

 the outer shore line there is still in a young 

 «tage of development, marked by an increase 

 of irregularity and raggedness over that of the 

 initial shore line; hence a recent date must be 

 given to the depression by wtieh the valleys 

 were drowned and the initial shore line of the 



present cycle was formed. Second, when the 

 recent depression of the region occurred, it 

 presumably caused the submergence of an 

 extensive lowland, worn down on a large area 

 of weak rocks north of Brittany in the second 

 cycle of erosion. Submergence thus formed 

 the western part of the English channel, and 

 brought the sea against the northern marginal 

 slope of the hard-rock upland of the earlier 

 peneplain, a little outside of the present clifE 

 line. When explained in this way, the north- 

 ern cliffs of the peninsula do not, in spite of 

 their height, indicate a great consumption of 

 the land by the sea, as has been supposed by 

 some authors. W. M. D. 



PHYSIOGRAPHIC TYPES 



The address delivered by the late Professor 

 Israel C. Eussell on ' Physiographic Problems 

 of To-day' at the Congress of Arts and Sci- 

 ence, Universal Exposition, St. Louis, in 1904, 

 is brought again to mind by its recent pub- 

 lication in the proceedings of the Congress 

 (Vol. IV., Boston, Houghton, Mifilin & Co., 

 1906, 627-649). One of its most suggestive 

 passages is concerned with ' ideal physio- 

 graphic types,' by which the author meant 

 " complete synthetic examples of * * * physio- 

 graphic forms, which will serve the role of 

 well-defined species in the study of the surface 

 features of the earth. Ideal types may be 

 likened to composite photographs. They 

 should combine critical studies of many actual 

 forms, within a chosen range, and in addition 

 be ideally perfect representations of the re- 

 sults reached by specific agencies operating 

 under the most favorable conditions. * * * A 

 well-arranged catalogue of ideal types would 

 be an analytical table of contents to the his- 

 tory of the evolution of the features of the 

 earth's surface, and constitute a scheme of 

 physiographic classification. * * * The selec- 

 tion of idealized physiographic types * * * 

 has for its chief purpose the reduction of end- 

 less complexities and intergradations to prac- 

 ticable limits. It is a method of artificial 

 selection so governed that, while no line in the 

 chain of evolution may be lost to view, certain 

 links are chosen to represent their nearest of 



