466 PHYSICAL GEOGRAPHY. 



buried in the earth." For myself, I am disposed to restrict the term 

 fossil to the remains, more or less perfect, of organized beings dating 

 anterior to the present epoch, if we can conscientiously speak of epochs 

 at all where the progression and rate of change have been so gradual. 

 Considered thus, then, these remains of diatomaceae cannot be classed 

 as fossils ; and at once the geologist perceives that they are to be taken 

 into account in a very different manner from what they have been hith- 

 erto. So much, then, for lacustrine sedimentary deposits of diatomaceae ; 

 and I trust that I have made clear as to what they are, and how they are 

 formed and forming. At the time I made his acquaintance, Prof. Bailey 

 expressed an opinion that similar strata would be found beneath every 

 bog and pond in the country. The clear scientific vision of my late 

 friend is evidenced in the fact that this prediction was proved almost lit- 

 erally true. I have over one hundred such specimens, and am continually 

 receiving others. Several I have already described, and others remain to 

 be examined, and facts with regard to the geographical distribution and 

 other 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 to 

 amount in thickness and extent, over- and underlying material, etc., 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 made up almost en- 

 tirely of the siliceous remains of fresh-water diatomacese. 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, spec- 

 imens 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 under- 

 stood, they have received various appellations, as "magnesia," "porcelain 

 clay," "white clay," "chalk," "siliceous marl," "microphytal earth," "trip- 

 oli," "rotten-stone," "pipe-clay" or simply "clay," "trachytal 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 



