CAM'BRIAN SYSTEM. The name given to the great series of sedimentary deposits which comes next in order of succession to the Archa an, the lower beds of the Cambrian system resting uneonfonnably on its upturned edges. The nanee Cainlirian, derived from Cambria. the ancient name of Wales, in which country the beds of this age were first recognized, was given by Adam Sedgwick, an eminent English geolo gist, who devoted his life to the study of this formation. Time upper limits of the Cambrian, as there studied, were in much dispute for a time, since many of the beds placed by Selig wick in the Upper Cambrian were claimed by Murchison to he Lower Silurian: and this, in deed, was subsequently found to be the case. To these disputed beds the name Ordovician (q.v.) was given by Lapworth (1879). Fossils are very scarce in the Cambrian rocks in many but in other localities, different members of the formation are exposed. life re mains showing a profusion of marine invertebrates and plants of low order. The animal remains include. in order of their im portance. crustaceans, brachiopods. pteropods, worms. gastropods, hydrozoans. echinoderms, sponges. corals. lamellibranchs, and cephalopods. All of these, except the cephalopods, were repre sented in the earliest periods of the Cambrian system.
While the great thiekness of Cambrian strata indicates a long period of sedimentation. still the great changes that we find in the faunas in passing from one division of the Cambrian sys tem into :1111411er are considered remarkable, since they indicate a most eomplete revolution in the life forms in any one region. Thus, of the many trilobites found in the Lower Candiri:111, hilt few are known in the middle division; and these, in turn, differ markedly fions those in the Upper Cambrian. The reason for this absence of transitional types may he title to the fact that the intermediate hedi eontoining them have not yet been discovered. The trilobites were a prominent feature of the Cambrian system, and varied much in size. from under an inch, like the small, blind ones, agnostus, to others having a of two feet, as paradoxides. No verte brate remains have been found. There is no
evidence of ipvertebrate life that existed on land in fresh water. although it is quite pos sible that some of the mollusks found may have lived in estuaries of brackish water, for the character of ninny of the sedimentary rucks of Cambrian time. such as grits, with ripple-marks. is indicative of shallow-water conditions.
The thickness of the Cambrian system is variable. In Newfoundland it is about (i000 feet; in Vermont and eastern New' York, 7000 feet ; in 'British ('olumbia, 10,000 feet, The Cambrian rocks include sandstones, limestones, shales, slates, marbles, and quartzites, with be ensbinal igneous rocks, as in the Lake Superior region and southeastern Pennsylvania, and also he Great Britain. The metamorphosed Cambrian rocks are found in areas of much folded strata. In America the Cambrian rocks have been classi fied under; I i ) qcorgimi series, or Lower Cam brian. a local development in Ali•higan being known as the keirecaurrorn, or liemetnian : iu this the trilobite olenellus is often common. (2) Acadian, or Iliddle Cambrian, in which the tribolite paradoxides is abundant in places. (3) Poisilain, or Upper Cambrian.
In North America Cambrian rocks are found in Yew found la nil, Nova Scotia, New Brunswick, and Canada; also in V'erinont, ,Ilassaehusetts, .Maine, New Hampshire, Rhodv• Island, New York. New Jersey, l'ennsylvania, .)Earyland, Tennessee, A la ba ma, ( teorgia, igan, Wis North Dakota, California. Colorado, Arizona. In foreign (quintries. they are known in Great Britain, Germany, Bohemia, Scandi navia, Prance. Spain. Sardinia. China, Australia, and India. The British, Bohemian. and Scandi navian areas are of interest. The e•o nomic products of the Cambrian system in the United States include the slates (q.v.l and limonite ore (q.v.) of the Appalachian States, sandstone in New York, and copper ores in Consult: Walcott, Tenth Annual Report nil( d Mates Geological ,'_;'urrcy (Washington, 1555) ; Bulb tin SI. United stairs Brological Surrey (Washingtim. 1591) ; Dana. Manual of Brology (New York, 1805) ; Trxi•book of (;eulogy ( London, 1503). See