26i THE CAUSES WHICH 



fern and reed, sink and become covered over as the former, and 

 so by continued depression the land surfaces eventually alternate 

 vertically with aqueous beds like the lettered sheets of a ledger. 

 When, lastly, the wreck 'of these zephyry scenes now lowered 

 to the sea level plunges bodily under the moaning waves and 

 becomes covered with drift-wood and sea-shells, sands and muddy 

 limestones ; then on cessation of the depression, a reflux of the 

 elevating force to this area acting on the teeming sea-bed, raises 

 the sunken surfaces as dark seams of coal j)arted by layers of 

 shales and sandstone (as shown in the diagram). This, the 

 common history of carboniferous accumulations in the northern 

 hemisjihere, is specially interesting to the entomologists^ as here 

 in excavating the nodules of clay ironstone at the ancient tree- 

 roots for the smelting furnaces, the workmen virtually dig out 

 the rusty infusorial scum left by this perpetually shoaling water, 

 enclosing impressions of its floatage of ferns and fruits, king- 

 crabs, myriopods, and insects. So, curiously enough, in seeking 

 a limestone flux to separate the metal, they blast the adjacent 

 marbles [e] replete with the well-known ammonite and sea-lily, 

 and once redolent of the foam that broke on the advancing 

 coral reefs. 



Standing on the purlieus of the black countries we may 

 with little difficulty evoke these ages of fern-crocheted glades 

 and shadow- chequered dells, embroidered and twinkling with 

 light fronds of Fecopteris and Sji^ienoj^teris, overshadowed by 

 tall gloomy beds of chafing reeds fifty feet in height, bare leaf- 

 scared stems and fir-like Lepidodendron, the giant analogues of 

 the ditch-side horse-tail and club-moss — dells and glades where 

 early insects crept and flew, such as tinkling leaf-crickets, 

 cockroaches [prtliopterd) , painted May-flies, dragon-flies, decay- 

 loving white ants {Neuropfera) , beetles {Coleoptera ?), mimetic 

 shepherd spiders and scorpions {Arachnida) , that lent animation 

 to a bright sunlight. Or we may look from out these dark 

 thickets, ferny brakes, and beds of wind-swept reeds, over a 

 vasty sea, unfurrowed as yet by the keel of the mariner, whose 

 summer calm was alone broken by the looming of a floating 

 nautilus, the whispering cat^s-paw, or the ripple of a bony 

 scale-fish — a scene of peace slumbering ai'ound early volcanic 

 centres that as ages glided by told out the course of time by 



