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 



Fig. 44.- Lithological Mickuscoi-k. 



action. They are hard from the heat 

 of the lava at the time it overflowed 

 the deposits. 



R. S. Warren., M. I). 



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- 



