*74 Canadian Record of Science. 



Book Notices. 



Bulletin TJ. S. Geological Survey. 1 — In this interesting and 

 valuable bulletin Mr. Russell describes the great deposits of red 

 clays, &c, resulting from the decay of the surface rocks in the 

 Appalachian Region, south of the southern limit of the glaciated 

 area, and then considers their bearing on the much debated 

 question of the origin of the red coloring matter of sandstones 

 and shales. 



Over large areas in Virginia and the Carolinas these residual 

 deposits are over 100 feet thick. The clayey material when washed 

 with water, leaves behind a residue composed of more or less 

 angular fragments of quartz and feldspar with scales of mica and 

 fragments of other minerals, each grain being coated with a thin 

 layer having a red or brown color, which is rich in ferric oxide 

 and alumina and may be described as a feruginous clay. This 

 coloring matter adheres firmly and is not removed by prolonged 

 washing, a fact which is illustrated by the red color of the sands 

 deposited by the streams of Virginia and the Carolinas in districts 

 underlain by crystalline rocks. Hot hydrochloric acid, however, 

 removes the coloring matter, leaving the grains with their normal 

 tints. The examination of a number of red sandstones showed 

 that their coloring matter was identical, both chemically and in 

 its mode of occurrence, with that in these residual deposits. 



Mr. Russell believes that when crystalline rocks become 

 thoroughly decomposed, especially in hot and moist climates where 

 decomposition takes place not only more rapidly, but more 

 thoroughly than in colder or drier climates, where rocks are often 

 disintegrated without suffering marked decomposition, tbe residual 

 deposits will be of a red color on account of the oxidatiou of the 

 iron contained in the original rock, not only in the form of pyrites 

 and magnetite, but also in various silicates such as pyroxene, mica, 

 &c. Such deposits are by no means confined to the Appalachian 

 Region, the terra rossa of Europe, the Laterite of India, and the 

 red earth of Bermuda being similar in character and origin. If 

 these deposits be washed away and redeposited, without prolonged 

 friction such as that produced by ocean waves, the transportation 

 being carried on by water which does not contain organic matter 

 or other agents which would affect the reduction and solution of 

 the iron, red sandstones and shales will be produced. 



1 Subaerial Decay of Rocks and Origin of the Red Color of Certain Formations. 

 Israel Cook Russell, Bulletin of the United States Geological Survey No. 52, 

 Washington, 1889. (pp. 65.) 



