CAMBRIAN SYSTEM. 91 



that the lowest forms of life should be the first and earliest 

 to reveal itself to the lenses of the palaeontologist ! 



Turning next to the CAMBRIAN system, so termed by 

 Professor Sedgwick, because well developed in the region 

 of Wales (the ancient Cambria), we find it for the most 

 part made up of crystalline schists and slates, hard siliceous 

 grits, and altered limestones. Like the Laurentian, its strata, 

 have undergone extensive metamorphism or internal mineral 

 change, and like the Laurentian, too, it is frequently inter- 

 sected by veins and eruptive masses of granite, and fels- 

 pathic greenstone. On the whole, however, its sedimentary 

 character is much more apparent ; its micaceous schists are 

 interstratified with grits and sandstones, and its slates often 

 earthy and more distinctly laminated. Taking it in the 

 mass of its 15,000 or 20,000 feet, it has altogether a more 

 recent aspect than the Laurentian, and bears, not only in its 

 sandstones and shaly slates, but in its imbedded pebbles, 

 ripple-marks, and tracks of marine worms, more decided 

 evidence of its aqueous origin. Of course, like other forma- 

 tions, the Cambrian will vary in composition in different 

 regions, sometimes being more slaty, and at others more 

 schistose and crystalline ; but slaty beds, micaceous flag- 

 stones, gritty sandstones, and limestones more or less crys- 

 talline, may be taken as the normal aggregate. 



When we turn to the fossils of the system we find them 

 also more numerous and intelligible than those of the Lauren- 

 tian, partly no doubt from the less metamorphism the beds 

 have undergone, but chiefly, perhaps, from that advancing 

 development of life we are accustomed to associate with the 

 newer and newer formations. At all events, instead of a 

 single organism, as in the Laurentian system, we now find, 

 if not a numerous, at least a fair array of zoophytes, echino- 

 derms, shell-fish, annelids, and Crustacea. The species are 



