150 STODDART^ ON MICKO-GEOLOGY. 



which this woody growth occurs, we find the shale dotted all 

 over. On magnifying these dots, the observer is startled at 

 finding thousands of the valves of Cypridaj and the little coiled 

 shells of Spirorhis, with many others that inhabit fresh waters. 

 From just such microscopic evidence we learn the fact that 

 coal is derived from coniferous trees, ferns and allied plants, 

 and also that those trees grew in marshy places, or covered 

 the estuary of some carboniferous river. 



The Triassic and Permian formations are nearly void of 

 microscopic fossils, except in a very few localities. 



In the Jurassic strata, which extend for many miles over 

 the counties of Gloucester, Somerset, and Dorset, are rocks 

 entirely made up of shell debris, Entomostraca, corals, and 

 Echinoderms. In the outskirts of Bristol are two such beds, 

 reaching over a very wide area full of the plates, spines and 

 jaws of sea-urchins. The whole bed is scarcely distinguish- 

 able at first sight from the shore of many parts of our present 

 sea-coast. In many places we find the shale-partings covered 

 with Cytheridae and Estheridse. The slabs of Oolite at Bath, 

 Minchinhampton, and Dundry, affbrd perfect specimens of 

 minute forms. It is, perhaps, in the Jurassic rocks, that the 

 miscroscope is especially valuable in the reading of shell 

 markings, for many Pectens, Limas, and Myarida3 so nearly 

 resemble each other, that the principal specific distinction is 

 the shell pattern; for in the fossil we have not the same 

 facility for specifying that we have in the recent animals. 

 Perhaps the most interesting of all to the micro-geologist, for 

 perfect and beautiful objects, are the fossil remains from the 

 Cretaceous and Tertiary beds. Whole countries are composed 

 of organic forms. A bed of hard limestone, traceable from 

 Africa to North America, is composed of Nummulites and 

 Orbitolites agglutinated together with powdered particles of 

 the same or other equally small creatures, each a wonder in 

 itself. The towns of Richmond and Petersburg, in Virginia, 

 are built on soil consisting of siliceous marl, twenty feet 

 thick. A microscopic examination shows this earth to consist 

 of frustules of Naviculee, Gallionellse, Actinocycli, Coscino- 

 disci, and others too numerous for mention, the largest of 

 which will not exceed ^-froth of an inch. 



The pyramids of Egypt and immense beds of the Pyrenees 

 and Alps are built up of foraminiferous limestone. 



These small microzoa seem to be the most ubiquitous of 

 any known beings; their flinty remains if diatoms, or cal- 

 careous if foraminifers, are found in the present day in count- 

 less numbers filling up rivers, as the Elbe and Nile; choking 

 up harbours, as on the Amazon, and Wersinar in the Baltic, 



