
PartrL§2] | ARCHASAN. 645 
trude at a number of points. Westwards of the central portion of the 
Alpine chain they rise in a more continuous belt, and show numerous 
mineralogical varieties, including protogine, mica-schist, and many other 
schists, as well as limestone and serpentine. But their most compact 
area, and most intelligible sections are to be found in the region that 
extends southward from Dresden through Bavaria and Bohemia between 
the valley of the Danube and the headwaters of the Elbe. They are 
there divided into two well-marked groups—(a) red gneiss, containing 
pink orthoclase and a little white potash-mica, covered by (b) grey gneiss, 
containing white or grey felspar, and abundant dark magnesia-mica. 
According to Giimbel the former (called by him the Bojan gneiss) may 
be traced as a distinct formation associated with granite, but with very 
few other kinds of crystalline or schistose rocks, while the latter (termed 
the Hercynian gneiss) consists of gneiss with abundant interstratifications 
of many other schistose rocks, graphitic limestone, and serpentine. The 
-Hereynian gneiss is overlaid by mica-schist, above which comes a vast 
mass of argillaceous schists and shales. In Bohemia these overlying 
crystalline clay-slates, and schists (Ktage A of Barrande) graduate up- 
ward into undoubted clastic rocks known as the Pribram shales, un- 
conformably over which come conglomerates and sandstones lying at the 
base of the fossiliferous series.1 In the Pyrenees the existence of 
Pre-Cambrian granites, with associated well-stratified masses of gneiss, 
mica-schist, limestone, &c., has been determined.’ 
America.—In North America Archean rocks cover a large part of 
the continent from the Arctic Circle southwards to the great lakes. In 
Canada, where they were studied in detail by Logan, they consist of two 
divisions. The lower of these, termed Laurentian, from its abundant 
development along the shores of the St. Lawrence, was estimated by 
him to be about 30,000 feet thick, but neither its top nor base has been 
seen. It has been divided into two series—(1) a lower formation more 
than 20,000 feet thick, consisting chiefly of granite, orthoclase gneiss, 
bands of quartz-rock, schists, iron-ore, and limestone containing the 
Hozoon above referred to; and (2) an upper formation fully 10,000 feet 
thick, composed also, for the most part, of gneiss, but marked by the 
occurrence of bands of Labrador felspar, as well as schist, iron-ore, and 
limestone. The upper division has been stated to lie unconformably 
on the lower. Mr. Selwyn, however, has recently contended that the 
limestone-bearing series rests conformably upon a massive granitoid 
gneiss, to which he would restrict the term Laurentian, classing the 
limestones in the next or Huronian system.® 
Above the Laurentian rocks in the region of Lake Huron lies a vast 
mass of slates, conglomerates, limestones, and quartz-rocks, attaining a 
depth of from 10,000 to 20,000 feet. They are termed Huronian. No 
1 The following references to descriptions of the Archean rocks of Central Europe 
may be useful. Saxony, &., Credner, Zeitsch. Deutsch. Geol. Ges. 1877, p. 757. Expla- 
nations accompanying the sheets of the Geological Survey Map of Saxony, particularly 
sections Geringswalde, Geyer, Glauchau, Hohenstein,. Penig, Rochlitz, Waldheim. 
Bavaria and Bohemia, Giimbel, Geognostische Beschreibung des Ostbayerischen | 
Grenzgebirges, Gotha, 1868 ; Jokely, Jahrb. Geol. Reichsanstalt. vi. p. 355; viii. p. 1, 516; 
Kalkowsky, “Die Gneissformation des Eulengebirges ” (Habilitationschrift), Leipzig 
(Engelmann), 1878. 
2 Garrigou, Bull. Soc. Géol. France, i. (1873), p. 418. 
3 Nat. Hist. Soc., Montreal, February, 1879. 
