Notes on the Igneous Rocks. 46l» 



ceding it (e.g., Augite Granite), or where a series of names 

 coming under a more general heading do not make up a 

 complete sub-classification, but merely indicate a series of 

 independent varieties (as in the case of Diabase), the type 

 has been shifted out of line to draw attention to the fact. 



In conclusion I desire to acknowledge the assistance 

 which I received in constructing this table from Prof. Eosen- 

 busch, who has devoted much time and thought to it. Most of 

 what there is of value in it originated with him. It must, 

 however, as Prof. Eosenbusch remarks, still be regarded as 

 of value rather for determinative purposes, and not as a 

 thoroughly satisfactory scheme of classification, which is a 

 thing to be looked for in the future. It is hoped, however, 

 that it may be one further step toward this goal. 



I also desire to acknowledge my indebtedness to Prof. 

 Geo. H. Williams of Johns Hopkins University, as well as 

 to the late Dr. J. Francis Williams of Cornell "University, 

 who have kindly aided me by several valuable suggestions. 



A Note on the Collection of Sediments in 

 Potable Waters. 



By E. F. Euttan, B.A., M.D. 



A point of considerable importance, but one frequently 

 overlooked by the analyst, is the microscopic examination 

 of the sedimentary matter occurring in drinking water. 

 This is generally described as "slight" "heavy" etc., 

 and little or no serious effort made to determine its general 

 nature. One explanation of this common omission is that, 

 as a rule, the quantity of sedimentary matter in a potable 

 water is very small and consequently very difficult to col- 

 lect for examination in a satisfactory way. 



The methods usually employed for collecting and estimat- 

 ing the traces of suspended solids present in most potable 

 waters are all open to objections. They are inefficient or 

 difficult of application. Probably one of the best, certainly 

 the one most frequently used, is to allow the vessel in which 



