114 
points, will be elucidated by such investigations; so that I 
am always anxious to receive contributions from all sources. 
It is only desirable that all facts connected with their mode 
of occurrence, as amount in thickness and extent, over- and 
under-lying material, &c., be noted at the time of making the 
gathering. 
We now come to consider deposits of an entirely different 
character from those just spoken of, but which yet are also 
gmade up almost entirely of the siliceous remains of fresh- 
water Diatomaceze. These are the so-called “ Infusorial” 
deposits, found in such enormous quantity in our Pacific 
States. From time to time, during the last thirty years, 
specimens of these have come into the hands of Naturalists 
from collectors and otherwise, and, also, “in place” they are 
well known to settlers in the districts where they occur. As 
their true character has not been understood, they have re- 
ceived various appellations, as “ Magnesia,” “ Porcelain Clay,” 
“White Clay,” “Chalk,” “Siliceous Marl,” “ Microphytal 
Earth,” “Tripoli,” ‘ Rotten Stone,” “ Pipe Clay” or simply 
“Clay,” “Trachytic Tufa” and “Phytolitharian Tuff” by 
Ehrenberg. These specimens are almost always white in 
‘color or nearly so, although there are records of some strata 
occurring of various tints. None of these except the white 
ones, have come under my observation, so I am not prepared 
to state that the colored onesare Diatomaceous. Besides this 
material is of a somewhat hard, stony character, but porous 
withal and light; as a general thing also it is readily broken, 
but not easily powdered as are the Lacustrine Sedimentary 
Deposits. On account of this hardness, there is found to be 
considerable difficulty in preparing these specimens for 
microscopical examination. After so preparing by a method 
I have devised, and viewing with a sufficiently high magnify- 
ing lens, this substance is found to be made up entirely of 
the siliceous remains of fresh-water Diatomacez, which have 
been matted together in the remarkable manner described. 
The species of Diatomaceze present however, are found to be 
very different in character from those to be seen in the other 
class of recently-formed deposits. Thus, whilst the genera 
