234 DR. THOMAS STERRY HUNT ON THE 
which dips in that direction beneath the Primal slates and Auroral limestones of the 
Appalachian valley. 
§ 43. In this remarkable section, it is evident that the crystalline rocks, upon which 
the Primal quartzite rests unconformably, belong to one or more older series, distinct from 
the Laurentian, and representing both the Huronian, and the petrosilex or Arvonian series. 
I was thus confirmed in my opinion, expressed in 1871, that the crystalline schists regarded 
by Rogers in this region as altered Lower Primal and Upper Primal, are both older than 
the Primal quartzites, and belong to one or more distinct series. These conclusions were 
announced in the Proceedings of the American Association for the Advancement of Science 
for 1876 (pp. 211, 212), and also in my Azoic Rocks, pp. 18 and 193. See further also the 
Amer. Journal Science for April, 1880 (vol. xix., p. 275), where they are described in 
connection with other localities of Huronian and Arvonian rocks. Frazer, who has since 
devoted much time to the study of the region, agrees with me in placing the crystalline 
rocks of the above section in the Huronian, including under that name the accompanying 
petrosilex-group ; and regards the quartzites as there forming the basal member of the 
Primal series. * 
§ 44. From the observations given in § 36, it is apparent that the Primal series of Rogers, 
where most largely developed in Pennsylvania, includes several repetitions of quartz- 
rocks, sometimes vitreous, sometimes granular, and occasionally detrital and conglomerate 
in character, alternating with softer schistose strata. This will be farther illustrated in a 
succeeding chapter, by observations in Virginia and elsewhere; when it will also appear 
that repetitions of these quartzites are met with below the horizon of the Scolithus-sand- 
stone. In many cases, a quartzite, often a conglomerate, is found to constitute the basal 
member of the series, which rests unconformably upon different groups of the older crys- 
talline rocks ;—Laurentian, Arvonian, Huronian or Montalban. Inasmuch as portions 
of the latter two groups were by Rogers confounded with the Lower Primal states, it will 
require careful examination, in each case, to determine whether we have really to do with 

the older rocks, or with strata belonging to his Primal series. 
Notwithstanding the division of the latter into Azoic and Paleozoic, based by Rogers 
upon the appearance, in the midst of the Primal, of the Scolithus-sandstone; it is to be 
remarked that the Primal slates, both above and below this horizon, really constitute, with 
the rocks of the Auroral, and a portion of the Matinal in the south-eastern area of Pennsyl-- 
vania, one great continuous series. Similar schistose and micaceous layers are found interca- 
lated alike among the Primal quartzites and the Auroral limestones ; while the accompanying 
masses of slate often include minor beds of quartzite, and others of granular limestone. The 
intimate relations of these various rocks were noticed by Rogers, who mentions what he 
calls “the alternations of Primal slate and Auroral limestone,” and “ the limestone at the 
passage of the Primal into the Auroral.” The Lower Primal slates were elsewhere 
described by him as alternations of talcoid silicious slate, talco-micaceous slate, and quartzose 
micaceous rocks, usually schistose ; besides other strata which are nearly pure clay-slate: 
Portions of the Matinal, in like manner, were said by him to be “a semi-crystalline clay- 
slate, partially talcose or micaceous.” Later studies have shown these strata to abound in 
hydrous micas, and more rarely to contain tale, chlorite, and related species. Some beds 

* Thèses présentées à la faculté des sciences de Lille, etc., 1882. 

