i68 THE POPULAR SCIENCE MONTHLY, 



resemblance to a coral-reef, instead of the aggregate of minute and 

 separate shells which formed the old Chalk, and which is even now 

 continuing the like formation. I do not know anj' more remarkable 

 result of microscopic inquiry, than the very distinct evidence it has 

 afforded, in well-preserved specimens of this Eozoon Canadense, of a 

 minutely tubular structure, which my own researches into the struct- 

 ure of the Foraminifera enable me to identify with certainty as be- 

 longing to that type. For we are thus carried back in geological 

 time to a period so extremely remote, that (as Sir William Logan re- 

 marked) the oldest fossils previously known are modern in compari- 

 son. The investigations of Sir Koderick Murchison have shown that 

 the equivalent of the Laurentian in this country is the " fundamental 

 gneiss " of Scotland, which (as I was shown a few days ago by my 

 friend Mr. Symonds, of Pendock) crops up in the Malvern Hills. Now, 

 in Central Europe this fundamental gneiss has a thickness of 90,000 

 feet ; and near its base Prof. Giimbel has recognized the equivalent 

 of the Canadian Eozoon^ which must have thus preceded the life of 

 what has been called the " primordial zone," corresponding to our 

 Cambrian rocks, by an interval of time so great that no geologist 

 would venture to assign a limit to it. 



The Cambrian series, consisting of the grits, sandstones, and slates, 

 that form the mountains of North Wales, scarcely contain any lime- 

 stone ; and we may pass from this to the /Silurian^ or Mid- Wales, 

 series in which we have the well-known Dudley limestone, as well as 

 other less important seams. A slab of Dudley limestone usually 

 shows an extraordinary variety of fossils, among which the most con- 

 spicuous are generally the beaded stems of Encrinites ; the joints of 

 these stems, when separated by the weathering of the rock, being 

 known in the north as " St. Cuthbert's beads." The whole of this 

 limestone is obviously made up of the corals, shells, crinoids, etc., 

 which we, find imbedded in it, and of a matrix formed by comminuted 

 fragments of the like types. A much greater development of these 

 calcareous beds presents itself in North America, the Trenton lime- 

 stone occurring in the lower Silurians, and the Niagara limestone iu 

 the upper; and these rocks have obviously been formed by the same 

 agency as the Dudley limestone. 



Passing on now to the Devonian series, we find beds of limestone 

 interposed among the sandstones, shales, and' conglomerates, of which 

 it is chiefly composed ; and these, like the Silurian limestones, are 

 made up of the fossilized remains of corals, shells, crinoids, etc., more 

 or less resembling those of earlier age. It is on the Old Red Sandstone, 

 which is here the uppermost member of the Devonian formation, that, 

 as I have already pointed out, our Carboniferous series immediately 

 rests ; its lower beds being distinguished as " limestone shales," on ac- 

 count of the interposition of seams of shale (formed of a mixture of 

 sand and clay) between the layers of limestone. 



