20 8 REVIEWS 



An interesting fact is the control of artesian head by the height of 

 ground water in the cover area, and several instances are adduced of 

 the head being raised by true influx of surface waters. Under the 

 most favorable conditions the head from the St. Peter and the Galena 

 appears to reach about 675 feet A. T., while from the Potsdam it 

 appears to rise slightly above 700 feet. Few wells in northern Illinois 

 can be depended upon to maintain a head much exceeding 600 feet A. 

 T. A few examples are added to the many on record of local artesian 

 regions whose head is lowered by over draft. In the Chicago district 

 the head of the St. Peter water has been drawn down nearly 100 feet, 

 and this loss of pressure extends ten miles and over west and south of 

 that part of the city where the wells are now numerous. At Joliet 

 heavy pumping of a single well has been found to lower the head 

 several feet in wells nearly one-half mile distant. The increase of 

 mineralization of artesian waters with increase of distance from the area 

 of intake is amply illustrated, sodium chloride, for instance, ranging 

 from about three grains to the gallon at Chicago to about 30 at Rock 

 Island and 277.7 ^t Barry. 



Of less interest to the geologist are the chapters treating of the 

 rainfall, the run off of the streams, and kindred topics. In the chapter 

 on the water supply of the cities and towns, the statement that "the 

 Chicago intakes are affected by sewage only when the Chicago River is 

 at high stages, which seldom amounts to more than a few days each 

 year," is certainly one that does not err from lack of moderation. 

 The final chapter, by Professor J. A. Udden, treats with fullest detail 

 of the artesian district of Rock Island and vicinity. The report is 

 amply illustrated with maps and sections, and it places on permanent 

 record a mass of valuable statistics in several fields. The details, how- 

 ever, are so handled that they do not interfere with the author's direct 

 and luminous treatment of the subject. W. H. Norton. 



The Geology of Santa Catalina Island. By William Sidney Tangier 

 Smith. Proceedings of the California Academy of Sciences, 

 3d Series, Geology, Vol. I, pp. 1-7 1, 2 plates and map. 

 The chief interest in this paper lies in the clear and generally con- 

 vincing manner in which the author has discussed the physiographic 

 problems presented by his very attractive field; his work being in that 

 respect a continuation of the previous work of Lawson. 



