File:Natural science- a monthly review of scientific progress (1896) (14767917184).jpg

Identifier: naturalsciencemo91896lond (find matches)
Title: Natural science: a monthly review of scientific progress
Year: 1896 (1890s)
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Publisher: London (etc.), Macmillan and Company (etc.)
Contributing Library: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library
Digitizing Sponsor: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library

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eries of north and south faults into the * Great Rift Valley. Itsfloor consists of ancient and modern lavas of various ages, thealluvium of dried lake basins, recent river gravels, and deserts of loosedrifting sand. Dr. Gregory was struck by the resemblance betweenthe lava-plains and those about the Snake River of Idaho, and con-siders these to have been produced by the combination of eruptionsfrom numerous centres, which he proposes to call plateau eruptions,rather than by outpourings from fissures. But the phenomena afforded by the Rift Valley are yet moreinteresting to the student of physical geology. The African lakes, asDr. Gregory points out, fall naturally into two classes : one long andnarrow, lying like fjords between steep cliffs; the other rounded inshape and with low shelving shores. Lakes of the former class occur ontwo lines, which pass on either side of the Nyanza and meet at LakeRudolf. Thence the line continues northward as a long strip of low 1896. SOME NEW BOOKS. 5S
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56 NATURAL SCIENCE. July, land, dotted with lakes and old lake basins, and sinking in placesbelow the level of the sea. It may be traced along the Red Sea,itself like a magnified fjord, up the Gulf of Akaba, and on throughthe Dead Sea and the Jordan Valley, till it ends on the plain ofNorthern Syria, after a course of about 4,000 miles. The trough-likeform of this sunken district is maintained throughout, and scatteredover its floor is a series of over thirty lakes, of which only one has anoutlet to the sea. A glance at the sketch-map in Dr. Gregorysvolume at once recalls to memory the outline presented by more thanone series of volcanic vents in the Pacific and Indian Oceans ; andthis African district, as we have seen, is a line of eruptivedisturbances as well as of faulting. In the Rift region the effect ofthe latter process has been no less remarkable than unusual. Stripsof country have been dropped down by a series of parallel faults, andthus a valley has been formed with precipit

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