838 



SCIENCE 



[N. S. Vol. XXVI. No. 676 



this peneplain has given opportunity for the 

 deep erosion of the Colorado canyon, and for 

 a moderate dissection of the weaker parts of 

 the uplifted area. Presumably before the time 

 of uplift, wide-spead eruptions of basalt oc- 

 curred in the southern part of the area; it is 

 to the capping of lava thus supplied that 

 remnants of the peneplain are preserved in 

 the localities studied by the author. At Black 

 point in the Little Colorado valley, a mono- 

 elinal fold involving compact sandstone and 

 weak marls is bevelled across by a very per- . 

 feet plain of erosion, upon which the basaltic 

 cover rests. In Anderson mesa, southeast of 

 Flagstaff, Arizona, a lava cap rests upon a 

 similar smooth surface, which bevels across 

 slightly inclined beds of resistant Upper Au- 

 brey limestones and weak overlying shales. 

 The lava sheet of Black mesa rests upon 

 Upper Aubrey limestones and sandstones 

 along the western border of the mesa, but 

 upon the overlying red beds farther east, thus 

 indicating a bevelling similar to that of the 

 other examples. Other localities afford evi- 

 dence of the same kind. The several pene- 

 plain remnants thus identified are believed 

 to represent parts of a once continuous and 

 extensive peneplain. Lava-capped baselevelled 

 surfaces in the Mt. Taylor district of New 

 Mexico farther east and in the Basin region 

 of Arizona farther west, are correlated with 

 the great peneplain of the Grand Canyon dis- 

 trict. 



The latter part of the paper is concerned 

 with a discussion of the drainage system of 

 the plateau district, with the conclusion 

 against the antecedent origin of the Colorado 

 River. There is much to be said in favor of 

 this conclusion, but the author's arguments 

 for it appear much less cogent than those 

 already cited regarding the peneplain. 



L>. W. J. 



THE ISTEIAN PENINSULA 



An elaborate study of the Istrian peninsula 

 at the head of the Adriatic by Dr. ISTorbert 

 Krebs of Vienna ("Die Halbinsel Instrien: 

 Landeskundliche Studie." Geogr. Abhand- 

 lungen herausg. von Professor Dr. A. Penck 

 in Berlin — formerly Vienna — Band IX., heft 



2, 1907) shows that it is a good-sized block 

 broken out of a well-worn-down mountain sys- 

 tem of close-folded Mesozoic limestones and 

 Tertiary sandstones with northwest-southeast 

 trend. A pretty good peneplain was formed 

 on the limestones, while the sandstones were 

 reduced to low rounded hills and ridges; then 

 the Istrian block was uplifted and tilted west- 

 ward, with a strong fault along the eastern 

 (Quamero) border; and in this position it was 

 submaturely or maturely dissected in later 

 Tertiary time, with abundant development of 

 karst features on the limestone areas; re- 

 cently the dissected block has been somewhat 

 depressed, so that the sea now enters its lower 

 valleys in river-like bays. 



To European geographers, who are already 

 familiar with these facts, Krebs' essay will be 

 easy and profitable reading, by reason of the 

 great body of pertinent details that it pre- 

 sents concerning matters of structure and 

 form. But to more distant readers, many of 

 whom must be unacquainted with the local 

 names and the physiographic history of the 

 peninsula, the essay will be difficult reading, 

 because the explanatory descriptions of the 

 larger features are almost lost in the wealth 

 of details concerning the minor features. 

 Only after reading nineteen pages, most of 

 which are given to geological matters, does 

 this geographical essay state the elementary 

 and essential fact that the surface of the 

 peninsula is not a structural (" geological ") 

 surface, but the final work of a process of 

 abrasion (das Endergebnis eines Abrasions- 

 vorganges) ; not until the twentieth page is 

 the inner and higher part of the peninsula 

 explicitly described as a monotonous plateau, 

 surmounted by rounded and isolated hills and 

 ridges; and not until the thirty-fourth page 

 is the lower western part of the peninsula 

 stated to be a slightly arched abrasion surface, 

 which may be regarded as a less elevated ex- 

 tension of the higher eastern part. 



W. M. D. 



STRUCTURE, PROCESS AND STAGE 



It would be an immense assistance to the 

 distant reader — and perhaps an aid to some 

 nearer readers as well — if substantial physio- 



