334 Reviews — Diagnostic Clear acteristics of Marine Clastics. 



Diagnostic Characteristics op Marine Clastics. By E. M. 

 Kindle. Bull. Geol. Soc America, vol. xxviii, pp. 905-16. 

 1917. 



rPHE author of this paper is very deeply and rightly impressed 

 -*- with the truth of the saying that " the present is the key to the 

 past ". He therefore brings forward some of his observations of 

 phenomena in present-day sediments which may be of use in deciding 

 whether rocks are of marine or freshwater origin. The points 

 considered are (1) the behaviour of fine sediment in fresh and salt 

 water, (2) the surface markings and textures developed during 

 sedimentation and during desiccation of muds, and (3) the 

 distinguishing characters of ripple-marks. In the first place it is 

 noticed that alternating layers of sandy and muddy material 

 deposited in salt Avater have more sharply defined boundaries than 

 those laid down in fresh water, owing to the comparatively rapid 

 flocculation of very fine sediment in salt water. 



Passing to the second section, it is explained that this flocculation 

 of clay is accompanied by small vertical currents, and that these 

 cause structures known as " pit and mound structures " on the 

 surface of the deposit. Structures produced during desiccation are 

 also different in freshwater and salt-water muds ; the " sun cracks " 

 of salt-water muds have level or turned down edges, while the edges 

 of these cracks formed in freshwater mjids are turned up. Further, 

 the texture of a dried saline mud is vesicular, and thus quite unlike 

 that of a freshwater mud. The question of ripple-marks is discussed . 

 at some length, and the author draws distinctions between those due 

 to current action and those due to wave action without forward 

 movement. The former type will be found to predominate in tidal 

 seas, while the latter is more prevalent in inland lakes ; it is also 

 noted that the ripple-marks produced by rivers will show evidence 

 of motion in one direction only, while those due to tidal currents 

 will indicate motion in at least two opposite directions. Though in 

 the opinion of the reviewer the author appears to be somewhat over- 

 sanguine, yet the points advanced in this paper seem to be worthy 

 of serious consideration when working through series of sediments 

 of doubtful origin. 



W. H. W. 



The Mineral Deposits of South America. By B. L. Miller 

 and J. T. Singewald, jun. pp. ix -\- 598, with 61 figures. 

 New York : McGraw-Hill Book Co., Inc. London : Hill 

 Publishing Co., Ltd. 1919. Price 25.9. 



WE cordially welcome this book, inasmuch as it gives us for the 

 first time a collected and accessible account of the great mineral 

 wealth of the South American Continent, from which came so much 

 of the fabled wealth of the Spanish galleons. The amount of detailed 



