November 1, 1894,] 



KNOWLEDGE. 



261 



Cambrian seas as they now bring the heated waters of the 

 Gulf of Mexico to the North Atlantic. 



StiU further, the sun and moon exerting their attractive 

 force as now would raise a tidal wave that would in the 

 narrow seas give with its ebb broad low-water beaches, and 

 ■ndth its flow rolling high- water waves to attack the coast-cliff 

 bases, and still further wear and round the shingle pebbles. 



Climate would vary as at present, with latitude and 

 distribution of land and sea, and so all the conditions 

 would be present to give graduated temperatm-es analogous 

 to those that now in various lands range from tropical 

 heat to Arctic cold. 



The seas of the Cambrian period were likewise, as those 

 of our epoch, some deep and some shallow, for both deep- 

 water deposits and shallow-water sediments make up the 

 Cambrian rocks. 



And throughout the millenniums of the Cambrian period 

 night would follow day and day would follow night ; 

 daylight would lengthen and strengthen, and daylight 

 would shorten and diminish ; and in the temperate zones 

 spring, summer, autumn and winter would complete 

 the year, while in the tropics the rainy seasons and the 

 dry seasons would alternate as now. 



These conclusions might have been drawn from even 

 the larger and more general phenomena of the Cambrian 

 rocks, but the beds of water-rolled pebbles, the ripple- 

 marki/igs, the sun-cracks, and the rain-pittings confirm 

 such conclusions. 



The palitontological evidence — that is, the evidence of 

 fossils — is as conclusive as the petrological evidence with 

 respect to the character of the climatal conditions of the 

 globe prevailing during the period of the deposition of the 

 Cambrian rocks. 



Although in the oldest of the Cambrians of the Long- 

 mynds of Shropshire and of North Wales the actual 

 remains of animals are few and obscure, yet the paired or 

 twin perforations in the sandstones can be none other than 

 annelid borings, that tell of the existence of sand- worms, 

 similar to those that abound on our present shores, and 

 so confirm the evidence of tidal beaches furnished by the 

 ripple-marks, sun-cracks, and rain-pittings. Casts of 

 fncoids, too, tell of marine vegetation like that now grow- 

 ing on sea-bottoms. 



But when we examine the Cambrians of Pembrokeshire, 

 we find remains of Crustacea of large size, and although 

 the great family, the Trilohitidie, has no representatives in 

 our present seas, yet trilobites in their general organization 

 so closely resembled the lobsters and crabs of the present 

 day that they must have required a generally similar 

 environment. Dean Buckland long since observed that 

 the eyes of trilobites indicate that there was the full light 

 of day when they lived. These wonderful organs of vision 

 were sessile and compound like those of the common crab, 

 though the lenses were round instead of hexagonal as in 

 our crustacean side-walking friend of the sea-shore, but the 

 facets were so numerous that as many as fifteen thousand 

 in each eye existed in some cases. Dr. Henry Woodward 

 thinks the eye of the trilobite may best be compared with 

 that of Limulux, and that there is an analogous development 

 of visual organs amongst some of the pelagic Amphipodm, 

 the Hyperiida, and in a very singular form brought home 

 by the " Challenger," the Tlmumops pelha-idd. 



In other Cambrian rocks, the Lingula Flags, are 

 abundant remains of Linf/iiIeUn, a genus or sub-genus of 

 a family of l^rachiopoda now well represented by the 

 Lini/ula chinensis of eastern Asiatic seas. This is perhaps 

 a more telling fact than the occurrence of an extinct group 

 of Crustacea, for not only was the living body of the 

 animal similar, and therefore suited only to similar general 



conditions, but the peculiar thin horny shell of the lingula 

 of to-day was exactly represented by the shell of the 

 LmgiilMa Ditvisii of the Lingula Flags, evidencing similar 

 materials in both the Cambrian and the present sea-waters 

 of the globe, as well as the same physiological powers for 

 its extraction and employment by the mollusc. 



Perhaps, however, even a still more striking proof of the 

 general cosmic conditions of the Cambrian period being the 

 same as those of the present epoch is afl^orded by the 

 occurrence in Cambrian rocks of species of a family of 

 Lamellibranohiata, the Arcidns, now abundantly represented 

 by well-developed and, so to speak, robust species in our 

 English seas. As I a long time ago pointed out, the 

 Cambrian Arcida3 and the abundance of members of the 

 family now, give a conspicuous proof of the marvellous 

 continuity of biomorphic types, or general organic form 

 and structure, from early geologic times to the present ; 

 and that great as is the generally interesting character of 

 this wonderful fact in itself, its significance or indirect 

 teaching is exceedingly great also, for it clearly indicates 

 the continuity of general inorganic conditions which must 

 have existed to allow of the uninterrupted succession of 

 generally similar organisms, all requiring, therefore, a 

 generally similar environment for their existence and 

 welfare, as well as for the development of the type. 



From the abundant evidence thus afforded of marine 

 organic existence living in Cambrian times as it does 

 to-day, we cannot doubt that the composition and density 

 of the water of the sea were practically the same as now, 

 and that both the sea and the atmosphere had the same 

 relations to light, the same optic powers — the same 

 absorptive, refractive, and reflective powers — as now. 



The teachings, therefore, of stratigraphical geology, both 

 petrological and palieontological, tell us in no uncertain 

 way that the general inorganic conditions on the surface 

 of the globe were during the Cambrian period very much 

 the same as they are to-day. So clear and unmistakable 

 is the evidence that we can with great confidence picture 

 to ourselves the ancient Cambrian world. 



We can see, as it were, its lands and its seas, its spread- 

 ing plains and elevated uplands, and its broad and deep 

 seas, with their shallower bays and gulfs. On the land, 

 too, are rushing torrents, rippling streams, and larger and 

 smoother flowing rivers, carrying eroded material to the 

 Cambrian ocean, fringed by sandy shores and shingly 

 beaches. And the sky above is now an unblemished azure, 

 now flecked with cirrus, and now dark with nimbus. Rain 

 falls, winds blow, tides ebb and flow, and we can see the 

 broad expanse of waters in their calm majesty or angry 

 with storm and tempest rolling mighty waves upon the 

 Cambrian strand, and we can think of the millions of 

 splendid sunrisings and gorgeous sunsets, and almost feel 

 the heat of the noontide summer sun or the cold of the 

 midwinter night. 



We can even look through the clear salt water on to the 

 ocean bed, and see the groves of algse, with the trilobites 

 and molluscs peopling those ancient seas, whUe along 

 their coasts volcanic fires at intervals break forth, and 

 lavas are outpoured that cover the surrounding rocks with 

 basaltic or trachytic coatings. 



But save for these volcanic outbursts, the crash of 

 thunder, and the roar of wind and wave, a silent world it 

 was. No lowing herds or roaring beasts of prey were on 

 the land, and no birds sang their songs either on tree-top 

 or high upon the wing. And how desolate was the un- 

 navigated sea, for whales and porpoises, seals and sharks, 

 and flying-fishes were not in its waters, and no sea-bird's 

 mew was heard, for no stormy petrel, gull, or penguin was 

 upon its surface. 



