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denser, components. The negative elements have, because of the relatively 

 greater density which they inherited from an original state, been able to 

 force the positive into higher positions during much of geologic time, so 

 that they are characterized by a greater thickness of fairly continuous 

 sediments. The positive elements found their levels of isostatic adjust- 

 ment to be higher, so that they have more often constituted our land masses. 

 The original relations of these components to one another has been greatly 

 modified by tangential pressure and igneous intrusions, making occasional 

 readjustments necessary; though the continent as a whole has maintained 

 its equihbrium with the exceptionally heavy oceanic segments. H. H. 



Peat, Essays on Its Origin, Uses, and Distribution in Michigan. By 

 Charles A. Davis. A part of the report for 1906 of the Michi- 

 gan Geological Survey, pp. 105-360, pis. XIII-XXXI, figs. 

 2-20, Lansing, 1907. 

 The author has very properly taken up the study of peat from a botanical 

 standpoint, though geological factors are by no means ignored. Michigan 

 peat is composed largely of the remains of plants which grew below or near 

 the water-level; sphagnum forms only shallow superficial deposits. The 

 living plant society varies as the development of a bog advances, for the 

 changed conditions created by one group of species may enable an invading 

 group to obtain a foothold where it was unable to live before the introduc- 

 tion of the earher group. We cannot, therefore, expect the flora at present 

 living in a swamp to indicate the quality of the underlying peat. A pecuUar 

 type of structureless peat was found which consisted largely of algal remains 

 with occasional diatoms and an abundance of the three-celled pollen grains 

 of conifers. Under proper conditions peat of this character would form a 

 deposit like the structureless cannel coals of the Carboniferous. Many 

 uses for which peat could be profitably employed are pointed out. In 

 Michigan, especially, peat coke might be made to bear a close relationship 

 to the iron industry. H. H. 



The California Earthquake of igo6. By David Starr Jordan and 

 Others. San Francisco: A. M. Robertson, 1907. 

 This volume contains a collection of articles, partly of a semi-popular 

 nature, by D. S. Jordan, J. C. Branner, G. K. Gilbert, S. Tabor, F. Omori, 

 H. W. Fairbanks, and Mary Austin, which had previously appeared in 

 various publications, together with a new essay by Charles Derleth, Jr., 

 on the effects produced by the earthquake on structures and structural 



