GEOLOGY. 



Dawn-animalcule, and consists of minute tubes 

 or cells that are visible only under the microscope. 

 Some still deny that this structure is organic, and 

 regard it as merely a mineral appearance ; but 

 these are few. The general opinion now is, that 

 here we have the earliest life-remains yet dis- 

 covered on our globe ; and this is all the more cer- 

 tain, that worm tracks and burrows were found 

 in 1866 in the same formation. The discovery of 

 these evidences of organic life, so long sought in 

 vain, shews that more minute search may result 

 in other remarkable discoveries, and that in all 

 likelihood the name of Eozoon will be found to be 

 premature. 



II. CAMBRIAN SYSTEM. 



Description. Immediately above the Laurentian, 

 lies a series of slates, schists, and crystalline lime- 

 stones, called the Cambrian System. It is so 

 named from being first most fully described as it 

 is found in North Wales, which in Roman times 

 was called Cambria. The rocks in this series are 

 less changed than the Laurentian, and therefore 

 the remains in them are more numerous and better 

 preserved. They are of great thickness, and are 

 found in Wales, Cumberland, Ireland, North Ame- 

 rica, and elsewhere. They are divided into two 

 groups, upper and lower. Along with the older 

 rocks beneath them, they everywhere form mighty, 

 rugged, peaked mountains, like those of Wales ; 

 and their worn, rugged aspect is due to their being 

 so long subjected to wasting influences from their 

 great antiquity. All these earlier rock-formations, 

 from the Laurentian to the Silurian, are exceed- 

 ingly rich in mineral wealth, most of the precious 

 metals being obtained from them. Shooting 

 through their hard crystalline masses, we find 

 veins of iron, copper, silver, and gold; and, from 

 the presence of these metals, bare mountain tracts 

 have teeming populations, where even the sheep 

 with difficulty finds its scanty food. 



Organic Remains. The fossil remains are all of 

 the very lowest kinds of life. Sea-weeds and shells 

 of different kinds have been discovered, and some 

 -Crustacea especially one that occurs abundantly 

 in the next formation, called the trilobite. The 

 tracks and burrows of worms, formed in the sand 

 of the ancient seas, may also be seen perforating 

 these hard masses. 



Scenery of Period. During the Cambrian age, 

 quiet seas heaved their waters as now, tenanted 

 with shells and crab-like creatures, while waves 

 rolled on the sandy shores, over which worms 

 crawled, and into which they burrowed ; facts inter- 

 esting as shewing that creatures had then the same 

 kinds of habits as now, and that what we can see 

 .any day along our own shores, sends us back to 

 the distant ages when the world was young. 



III. SILURIAN SYSTEM. 



Description. The Silurian System contains 

 rocks less changed by heat than those below, and 

 exhibiting more abundant life. In many of those 

 already mentioned, the metamorphism has been 

 so great as to render it difficult to say with cer- 

 tainty how the rocks were originally formed, but 

 henceforth all hesitation vanishes. They form 

 two groups, Upper and Lower Silurian. They con- 

 tain slaty sandstone, finely laminated, and often 



exhibiting ripple-marks ; conglomerates chiefly of 

 rounded pebbles, clays, and limestones, with corals 

 and other fossil remains, all of great thickness. 

 The system has received the name of Silurian 

 "rom being very fully developed in a part of South 

 Wales anciently called Siluria. 1 From these rocks 

 are obtained roofing-slates, freestone for building, 

 flagstones for paving and other purposes, lime- 

 stones from which lime is got by burning, and 

 valuable ores of lead, copper, silver, mercury, 

 and gold. 



Organic Remains. Parts of the stems and leaves 

 of water-plants and club-mosses, and a few sea- 

 weeds, are found, but all scarce and much broken. 

 No land animals have yet been obtained, and 

 though it would be rash to say that they do not 

 exist, much seems to render this very prob- 

 able. But marine fossils are numerous and well 

 marked, some of them being very beautiful We 

 find corals of different kinds, named according to 

 their appearance, such as the sun, star, cup, pipe, 

 chain, spider, and honeycomb corals. One of the 

 commonest forms in the Silurian rocks is a very 

 Deautiful curved creature like the plume of a 

 oose-quill, called the Graphitic? from looking 

 [ike &pen on the rock; some single, others double, 

 some straight, others beautifully spiral. Another 

 very abundant form is the Encrinite, a coral crea- 

 ture more numerous in the Carboniferous System. 

 We find also star-fishes, one beautiful and ' almost 

 as uncompressed as if just washed up on the sea- 

 beach,' 3 and numerous fine shells with single and 

 double valves, some, like the periwinkle and cockle, 

 being abundant. But the creature that swarmed 

 most in the ancient Silurian seas was the Trilobite^ 

 so called from its body consisting of three lobes or 

 divisions, above which was set its head with large 



Coral (Astrta}. 



Trilobite (Asaphus de Buckii). 

 Silurian Fossils. 



double eyes, still to be found entire. It had various 

 forms, and seems to have been very active, and 

 was of all sizes, from mere specks to fine speci- 

 mens ten or twelve feet long. Creatures like the 

 scorpion, with toothed toes, are also obtained, and, 

 in the upper beds, fishes interesting as the most 

 ancient fossil-fish. 



Scenery of Period. Of the dry land, we know 

 little or nothing, except that it did exist, and 

 nourished certain aquatic plants and club-mosses, 

 whose remains were floated down into the great 

 seas. But we can see mighty oceans, in which 

 corals flourished, and encrinites waved their lily 

 stems. Shells were abundant, and numerous crea- 

 tures gambolled in the bright sun. These seas 

 were fringed by sandy shores, on which worms 



Inhabited by the ancient tribe of the Silurts. 



* From Greek graphs, I write, and litkos, a stone. 



The VaUetuttr asptrinus. See Lyell's SttUtnft Eltmtntt, 



' From Greek treit, three, and lobos, a lobe. 



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