TACONIC QUESTION IN GEOLOGY. 228 
Potsdam sandstone were, by Emmons, declared to be represented, to the eastward, by the 
great development of strata included in the Sparry Lime-rock and the First Graywacke, to 
which, as a whole, he gave the name of Taconic slates, and later that of Upper Taconic. 
He farther declared, in 1861, that the primordial zone in Bohemia, which includes Bar- 
rande’s first fauna, “is in co-ordination with the upper series of the Taconic rocks.” * 
The name of Ordovician (sometimes contracted to Ordovian) which we have intro- 
duced in this table, was proposed by Lapworth in 1879 + to designate the group of paleozoic 
rocks found in Wales between the base of the Lower Llandovery and the base of the Lower 
Arenig. These, corresponding essentially to the Upper Cambrian or Bala group of Sedg- 
wick—the second fauna of Barrande—were, as is well-known, by a mistake in stratigraphy, 
joined by Murchison to his Silurian system, under the name of Lower Silurian; and have 
also since been called Siluro-Cambrian and Cambro-Silurian. By making of this debated 
ground, a separate region between the true Silurian abeve and the great Cambrian series 
below, (the Middle and Lower Cambrian of Sedewick) Lapworth has sought to get rid of 
the confusion in nomenclature, and to restrain the attempts of some to extend the name 
of Silurian downwards even to the base of the Cambrian itself. This new division is con- 
venient in American geology from the fact that it includes the group of strata between the 
base of the Silurian (Oneida) sandstone and the base of the Chazy limestone; the latter, 
together with the Trenton, Utica and Loraine divisions, being equivalent to the Ordovi- 
cian. The name was given in allusion to the Ordovices, an ancient British tribe inhabit- 
ing North Wales. 
§18. We have placed at the base of the column as representing the gneisses and 
other crystalline rocks, (Eaton’s lower division of the Primitive series), the names of five 
groups: Laurentian, Norian, Arvonian, Huronian and Montalban, the distinctness of which, 
in our opinion, is now established alike on stratigraphical and lithological grounds, both 
in North America and in Europe. Of these, the Laurentian, or older gneissic series, will 
probably require sub-division, and the separation of the typical Laurentian, represented in 
Canada by what has been called the Grenville series, from the underlying Ottawa gneiss. 
Both of these were, however, included in the Lower Laurentian on Logan’s maps of Canada ; 
the Norian being thereon called Upper Laurentian, or Labradorian. This is provisionally 
placed below the Arvonian or petrosilex-series, which was at first included, in North 
America, in the base of the Huronian. The latter is the great greenstone-series, which, in 
the Alps, intervenes between the ancient gneiss and the younger gneiss and mica-schist 
series. This is the Montalban, which, in the absence of the intermediate groups, is found, 
in many places, resting directly upon the older gneiss. For a historical sketch of the 
progress of discovery in these older rocks, see the author’s report on Azoic Rocks, in 1878 ; 
also, his paper in 1880 on The pre-Cambrian Rocks of Europe and America Compared ; and, 
farther, on The pre-Cambrian Rocks of the Alps, being a chapter on his recent essay on 
The Geological History of Nerpentines, in 1883. * 
The following words, published in 1874, before the recognition of the Arvonian, 
are still applicable: “The distribution of the crystalline rocks of the Norian, Huronian and 

* Emmons, Manual of Geology, page 89. 
+ Geological Magazine, vi., p. 13. 
f Azoic Rocks, Report E. of Geol. Survey of Pennsylvania, 1878; American Journal Science, 1880, vol. xix, 
pages 268-283; Trans. Royal Soc. Canada, 1883, pp. 152-196, 
