January 24, 1902.] 



SCIENCE. 



155 



remarkably even. The ridges often have 

 nearly level crest-lines for several miles, and 

 rise to similar altitudes; and there are some 

 extended flats at the height of the ridge tops. 

 Southward from the mountains there is a 

 lower and yoiuiger and much better preserved 

 peneplain, uplifted a few hundred feet, slop- 

 ing gently toward the sea and sharply trenched 

 by young valleys 'the most beautiful and per- 

 fectly base-leveled land' that the writer has 

 seen. The interfluves are very slightly arched 

 and are remarkable for their long gentle 

 slopes. Many low monadnocks rise above the 

 plain, and these, together with a 10- or 30-mile 

 belt of irregular ridges and peaks bordering 

 the mountains, are taken to be the remnants 

 of the older peneplain, here less preserved than 

 in the harder rocks of the Cordillera. The 

 border of the younger peneplain, determined 

 by the ending of its gently undulating strata, 

 is followed by a young coastal plain, trenched 

 like the peneplain by narrow valleys and 

 cliffed along the shore; here the interfluves 

 are flat, instead of being gently arched as fur- 

 ther inland. The coastal plain, as an area of 

 marine deposition, is the equivalent of the 

 younger peneplain as an area of subaerial deg- 

 radation. On the northern side of the isth- 

 mus, a narrow, dissected peneplain slopes 

 gently from the Cordillera to the seacoast. 

 This plain bears auriferous gravels near the 

 mountain base. The slopes of the two younger 

 peneplains, north and south of the Cordillera, 

 and the greater height that is believed to have 

 been gained by the older peneplain along the 

 mountain axis, suggest a repeated up-arching 

 of the isthmus along an east-west line. A 

 recent depression has occurred, especially 

 noticeable along the southern coast, where 

 there are several good examples of partly 

 drowned valleys. 



THE GRECIAN ARCHIPELAGO. 



Philippson's latest studies in classic lands 

 concern the Cyclades or southern island 

 group of the Grecian archipelago ('Beitr. zur 

 Kenntniss der grieeh. Inselwelt,' Pet. Mitt. 

 Ergdnzungsheft, 134, 1901, 172 pp., 4 maps). 

 The islands are, in the most general state- 

 ment, the remains of an old-mountain region 



(Eumpfgebirge) reduced to moderate but not 

 faint relief, then elevated and much dissected 

 by streams and waves during slow depression, 

 finally more rapidly submerged and again 

 vigorously attacked by the sea. The geo- 

 logical structure is irregular and not clearly 

 related to the distribution of the individual 

 islands. The old-mountain uplands are best 

 preserved where the rocks are somewhat uni- 

 formly resistant, as on Andros; elsewhere, 

 variety of structure leads to variety of form, 

 Naxos being of most rugged relief. The val- 

 leys are rather sharply incised beneath the 

 uplands; the author parenthetically notes that 

 they would be called 'young' by American 

 morphologists. They represent the headwater 

 parts of what was once a much more extensive 

 drainage system, developed while the land 

 stood higher than at present. During that 

 time the sea is believed to have actively 

 abraded the coast, producing a platform of 

 tolerably even surface from three to fifteen 

 miles wide, with greater breadth on the ex- 

 posed than on the protected sides of the 

 islands. The depth of the platform decreases 

 from about 200 met. at its outer border to 

 about 80 or 50 met. near the islands; and 

 hence a slow depression is inferred during 

 abrasion. Then came the more rapid submer- 

 gence, bringing the sea about to its present 

 level on the steep coast that had previously 

 been cut around the remnant islands, and 

 transforming the valleys into bays whose depth 

 corresponds to that of the inner border of 

 the submerged platform. The exposed parts 

 of the present shore line are usually bold and 

 ragged. Few of the islands have lowland 

 plains, those on the western side of Naxos 

 being the largest. 



In not making explicit mention of the work 

 of subaerial erosion during the inferred 

 abrasion of the now submerged platform, 

 Philippson's summary may give the impres- 

 sion that the greater part of the old-mountain 

 uplands were consumed by the sea. It is prob- 

 able, however, that many deep and broad val- 

 leys were eroded in the original uplands by 

 streams, while the outer border of the platform 

 was cut away by the waves; and that the fur- 

 ther abrasion by the sea was aided not only 



