MICROSCOPIC GEOLOGY '. LEVANT MUD. 755 



same manner, or (still better) by burning to a white asb a speci- 

 men of Coal that has been previously boiled in nitric acid, and then 

 carefully mounting the ash in Canada balsam ; for mineral ' casts ' 

 of Vegetable Cells and Fibres may often be distinctly recognized in 

 such ash ; and such casts are not unfrequently best afforded by 

 samples of Coal in which the method of section is least successful 

 in bringing to light the traces of Organic structure, as is the case, 

 for example, with the Anthracite of "Wales. 



588. Passing-on now to the Animal kingdom, we shall first cite 

 some parallel cases in which the essential nature of deposits that 

 form a very important part of the Earth's crust, has been deter- 

 mined by the assistance of the Microscope ; and shall then select 

 a few examples of the most important contributions which it has 

 afforded to our acquaintance with types of Animal life long since 

 extinct. — It is an admitted rule in Geological science, that the 

 past history of the Earth is to be interpreted, so far as may be 

 found possible, by the study of the changes which are still going 

 on. Thus, when we meet with an extensive stratum of fossilized 

 Diatomacece (§ 236) in what is now dry land, we can entertain no 

 doubt that this Siliceous deposit originally accumulated either at the 

 bottom of a Fresh-water lake or beneath the waters of the Ocean; 

 just as such deposits are formed at the present time by the produc- 

 tion and death of successive generations of these bodies, whose in- 

 destructible casings accumalate in the lapse of ages, so as to form 

 layers whose thickness is only limited by the time during which 

 this process has been in action (§ 235). In like manner, when 

 we meet with a Limestone-rock entirely composed of the Calca- 

 reous shells of Foraminifera, some of them entire, others broken 

 up into minute particles, we interpret the phenomenon by the fact 

 that the dredgings obtained from certain parts of the Ocean - 

 bottom consist almost entirely of remains of existing Foraminifera, 

 in which entire shells, the animals of which may be yet alive, afe 

 mingled with the debris of others that have been reduced by the 

 action of the waves to a fragmentary state.* Now in the fine 

 white mud which is brought-up from almost every part of the sea- 

 bottom of the Levant, where it forms a stratum that is continually 

 undergoing a slow but steady increase in thickness, the Microscopic 

 researches of Prof. Williamson f have shown that not only are 

 there multitudes of minute remains of living organisms, both 

 Animal and Vegetable, but that it is entirely or almost wholly 

 composed of such remains. Amongst these were about 26 species 



* Such a deposit, consisting chiefly of Orbitolites (§ 376), is at present 

 in the act of formation on certain parts of the shores of Australia, as the 

 Author is informed by Mr. J. Beete Jukes; thus affording the exact 

 parallel to the stratum of Orbitolites (belonging, as the Author's investi- 

 gations have led him to believe, to the very same species) that forms 

 part of the ' Calcaire Grossier ' of the Paris basin. 



t " Memoirs of the Manchester Literary and Philosophical Society," 

 Vol. viii. 



3 C 2 



