PALEOZOIC TIME — CAMBRIAN. 463 



Potsdam Sandstone, Neic York Geol. Survey, 1842. Primal Sandstone, H. D. and 

 W. B. Eogers. Upper Taconic, fossiliferous slates of Georgia, etc., E. Emmons, 1844, 

 1846 (not in the Taconic System of 1842) . 



History of the terms Cambrian and Silurian. — The terms Cambrian and 

 Silurian recognize the united labors of Murchison and Sedgwick in the first 

 careful study, in Great Britain, of the older fossiliferous rocks of Paleozoic 

 time. The two eminent English geologists worked together in some of their 

 earlier investigations. The memoirs of that period, ''Communications on 

 Arran and the north of Scotland, including Caithness (1828) and the Moray 

 Firth, others on Gosau and the eastern Alps (1829-1831) ; and still later, in 

 1837, a great memoir on the Paleozoic strata of Devonshire and Cornwall, 

 and another on the coeval rocks of Belgium and north Germany, show the 

 labors of these intimate friends combined in the happiest way — the broad 

 generalizations in which the Cambridge professor delighted, well supported 

 by the indefatigable industry of his zealous companion." ^ In 1831, they were 

 both at work " without concert " on the borders of Wales, — Murchison chiefly 

 on the English side and in southern Wales, and Sedgwick beyond the bound- 

 ary in north Wales. Sedgwick had earlier investigated somewhat similar 

 rocks in the Cumbrian Mountains. By 1834, Murchison had laid down his 

 grand divisions of Ludlow, Wenlock, Caradoc, and Llandeilo, and had referred 

 the first two of them, on the ground of the wide difference in fossils, to the 

 Uliper Silurian, and the latter two to the Lower Silurian. In 1835, the terms 

 Cambrian and Silurian appear together in a combined paper presented by 

 the two authors to the first meeting of the British Association. Silurian 

 had been announced by Murchison nearly two months before in the July 

 number of the Philosophical Magazine. In 1838, each put forth more fully 

 his results : Sedgwick, in a paper read before the Geological Society, giving 

 the distribution and character of the rocks, with but little notice of the char- 

 acteristic fossils ; but Murchison, before the close of the year, in a quarto 

 volume of 800 pages copiously illustrated with figures of fossils and geologi- 

 cal sections, entitled the " Silurian System." Murchison's work and his 

 names of subdivisions came into immediate use in all countries, and were 

 recognized in all geological treatises. 



Gradually it came to light that the Lower Silurian of Murchison com- 

 prised rocks and fossils of the age of the Upper Cambrian ; and also that 

 the fossils from beds of still lower level differ little in general type from 

 those of the Lower Silurian. Thus geologists, with Murchison's book in 

 hand, were led to use the term Loioer Silurian for the fossiliferous Cambrian. 

 No full account of Sedgwick's Cambrian fossils was published before 1852 

 to 1855, and not even lists of species before 1843. 



In 1846 Sedgwick made his first protest against the absorption of the 

 Cambrian by the Lower Silurian of Murchison ; and in 1852 the controversy, 

 thus begun, ended in his claiming the whole of the Lower Silurian as Upper 



1 Professor John Phillips, Nature, Feb. 6, 1873. 



