OF THE DIATOME-E. 85 



present surface, and close upon the rock which forms the original bed of this 

 estuaiy, the mind is irresistibly led to the conclusion that they have existed 

 there from the time when the waters fii'st rolled over the spot." 



Berg-mehl, Tripoli, and other polishing-powders, the stratified deposits at 

 Bilin in Bohemia and in ^gina, and numerous others examined and reported 

 on by various microscopists might like"\vise be adduced to demonstrate the 

 important part played by these individually in\-isible beings, when accumu- 

 lated in countless mpiads, in the construction of the earth's cnist. 



The Oolitic, and even some earlier metamorphic rocks, poq^hpitic rocks, 

 &c., are not wanting, according to Ehrenberg, in species of Diatomeae ; but 

 in the Pliocene, Miocene, Eocene, and in chalk and flint, and still more in 

 the tertiary deposits, the abundance and variety of forms are greater. Diato- 

 maceous shells are cuiiously preserved to us in large abundance and perfec- 

 tion in guano, in which they have doubtless entered as a component in the 

 way of mixture Tvith food taken by the bii'ds which have deposited that 

 manui'e. 



The foregoing facts teach us that probably, in the present condition of our 

 planet, no portion of its siuface is destitute of Infusorial life ; and now, from 

 the prosecution of microscojDic research in connexion with geological facts, 

 it would appeal' that, under this simplest and primary form, organic Hfe made 

 its fii'st appearance on the globe, and has, during the many epochs of this 

 world's histoiy, and notwithstanding the mightiest changes its suiface has 

 undergone, been sustained imtil the present moment ; and, what is more, so 

 extraordinaiy is the capability of the silicious Diatomeae to preserv^e life, and 

 so astonishing theii' powers of multipHcation, that species which are now 

 found li\ing have their generic and even their specific types at the very 

 da^vn of creation. Prof. Ehrenberg has advanced this same statement in his 

 recent work (Mikrogeologie), saying that the oldest sihcious Infusoria, whe- 

 ther Carboniferous or Silurian, belong to the same genera, and often to the 

 same species. 



Aeeolitic Diatome^. — Ehrenberg was the first to demonstrate the fre- 

 quent existence of Diatomeae along with other microscopic beings and or- 

 ganic particles in the atmosphere, principally in those showers of dust which 

 fall from time to time in various parts of the world, and in those other mete- 

 oric products known by the name of ' meteoric paper ' and ' blood-rain.' In 

 such atmospheric productions, the Berlin natui^alist has detected above a hun- 

 di^ed species ; these, accompanied by descriptions and figm^es, and prefaced 

 by an account of aU such atmospheric phenomena on record, were pubhshed 

 by Ehrenberg in a large brochure entitled " Passatstaub unci Blutregen/' 

 consisting of 192 foho pages. An extract from this book wiU convey the 

 best attainable notion of the physical importance of these aerial dust-showers. 

 The quantity of actual solid matter that has fallen from the atmosphere 

 by showers is far more considerable than supposed ; for, though it falls in a 

 diffused dust-like form, the extent of surface covered at any one time is 

 veiy considerable. Comparing it vdth. meteorolites, Ehrenberg obsei-ves that 

 the total quantity of these stones which fell between 1790 and 1819 weighed 

 600 cwt., while in a single dust-shower at Lyons, in 1846, the soHd matter 

 weighed fuUy 7200 cwt. Other dust-stoims in Italy, at Cape de Yerd, and in 

 other localities have exceeded even that at Lyons, in the quantity of matter 

 precipitated to the earth ; and Ehrenberg suggests to the imagination the 

 millions of tons that must have fallen since the time of Homer. Lastly, he 

 entertains the ciuioiLs opinion, that this meteoric dust does not necessarily 

 derive its existence from the earth's surface, and from the force of atmospheric 

 currents, but from some general law of the atmosphere, according to which 



