226 



THE AMERICAN MONTHLY 



[December, 



regard to filtered water, I had in mind 

 soft water, such as I had been in the 

 habit of using, and not water obtained 

 in calcareous ground. Such water, 

 thoroughly filtered, can hardly, I 

 think, be practically different from 

 distilled water. 



The name "sub-plutonic" has been 

 given to diatomaceous deposits found 

 under beds of lava. They are found 

 in regions where, in the geological 

 changes, there have been great up- 

 heavals, subsidences, and volcanic 



Mr. Stodder confirms the above. Mr. 

 Stodder writes : " I was surprised by 

 the resemblances ; " the difference 

 is "mostly in phraseology." This is 

 only one of many curious coinci- 

 dences which abound in literature. 



—Ed.] 



o 



Lithological Microscope. 



The application of the microscope 

 to the examination of rocks has be- 

 come of great value to the lithologist 

 and mineralogist. Not only has the 

 microscope thrown much light upon 

 the origin of rocky strata which con- 

 tain the remains of organic forms, 

 but it has also led to a knowledge 

 of the mineralogical composition of 

 rocks, and of the transformations 

 which they have undergone, far more 

 intimate and certain than chemical 

 analysis could ever afford. We illus- 

 trate this month one of the many 

 forms of petrological microscopes 

 now to be obtained. It is an English 

 instrument, made by Mr. Watson, of 



Lithological Microscope. 



action. They are hard from the heat 

 of the lava at the time it overflowed 

 the deposits. 



R. S. Warren., M. D. 



Colorado Springs. 



[A previous communication from 



London, which has proved quite satis- 

 factory to those who have used it. 

 Stands for the same purpose are made 

 by Mr. Bulloch, and the " acme litho- 

 logical " is sold by Messrs. Queen & 

 Co. and by Mr. Woolman. Our read- 



