240 THE CAMBRIAN. (bull. 81. 



With the exception of the Bala and Arenig series the system is essen- 

 tially the same as that generally accepted by the English geologists at 

 the present day. 



As geologist of Tennessee, Dr. Gerard Troost read Sir R. I. Murchi- 

 son's Siluria, and also the observations of Prof. Sedgwick on the Cam- 

 brian rocks of Wales. Discussing the changes in nomenclature made 

 necessary in expressing the views of Messrs. Murchison and Sedgwick, 

 he says in 1841:1 



After having pointed oat, in my last report, the line of junction of the primordial 

 or crystalline rocks in East Tennessee, I mentioned that the country west of the lino 

 which separates Tennessee from the State of North Caroliua is composed of gray- 

 waeke, slate, limestone, etc. All this country, according to the views of Murchison 

 and Sedgwick, belongs to a new division, which they call the Cambrian system. 



He then proceeds to describe the geographic distribution of the rocks 

 that he referred to the Cambrian system, identifying the series in Ten- 

 nessee with that of Wales entirely upou its lithologic characters and 

 the absence of organic remains, and from the fact of its being suc- 

 ceeded by a series of limestones from which he obtained and identified 

 Silurian fossils. 



The presence of the equivalent of the Cambrian system in America 

 was clearly recognized by Dr. E. Emmons, who, in 1841, wrote: 



There are, however, if I understand Mr. Sedgwick and Mr. Murchison, rocks still 

 lower; those which are now considered by them as metamorphic. They are the 

 lower masses which I considered as equivalent to the Taconic rocks; the Lower 

 Cambrian of Sedgwick, and not the Upper, which latter I proved to belong to the 

 New York system. That the Taconic slate is precisely that in which the Nereites in 

 Wales occur, there is not the slightest doubt in my own mind, and this is that part of 

 the Taconic system which we can see lying unconformably beneath the oldest mem- 

 ber of the New York system, and hence of the Silurian also. I know not, however, 

 whether in Wales the same limestones, slates, and quartz rocks are to be found which 

 we have here, and which are the oldest parts of the Taconic system. These are facts 

 to be determined. Their non-existence in Wales, however, does not destroy the sys- 

 tem. Very important members are known there, and should the lower slates and 

 quartz be found wanting, it only proves the absence of that development which is so 

 well known here in New York, Massachusetts, Vermont, and Maine, and I may add, in 

 Michigan also. 3 



Under the influence of the publications of Sir R. I. Murchison, Amer- 

 ican geologists, other than Drs. Troost and Emmons and the latter's fol- 

 lowers, classified all the Lower Paleozoic rocks under Lower Siluriau, 

 entirely ignoring Cambrian except to state that it was equivalent to the 

 Lower Silurian. In 1872, however, Dr. T. S. Hunt published his history 

 of the names Cambrian and Silurian in geology, advocating the recog- 

 nition of the term " Cambrian." 3 



1 Sixth annual report of the geological survey of Tennessee by the State geologist. Nashville, 1841, 

 p. 171, doc. ed., p. 4 of special ed. 



2 The Taconic System, 1844, p. v. 



8 Canadian Naturalist, new ser., vol. 6, 1872, pp. 281-312, 417-448. Geological Magazine, vol. 10, pp, 

 385-395, 453-461, 504-510, 561-566, 1873. 



