ARCILEAN TIME. 157 



talline form of nephelite, evincing that it was made out of preexisting nephelife 

 crystals, like the gieseckite of Greenland, which it resembles in aspect and com- 

 position. Another species, loganice, has the forms of pyroxene. Other evidences of 

 alteration subsequent to the original crystallization are the rounded crystals of quartz 

 and apatite of Gouverneur, and the soft spinels of St. Lawrence County, called houghite 

 or hydrotalcite. In view of the remoteness of the Archaean era, and also of the 

 chemical powers of water, especially when charged with heat and therefore with alkalies 

 and silica, such changes are not a source of wonder. 



Igneous or eruptive rocks. — There are few examples of dikes of igneous 

 rocks, through the Laurentian of Canada ; and these are mostly confined to the county 

 of Grenville. The dikes there are of four different periods of eruption. The oldest, 

 as Hunt observes, consist of greenish-gray doleryte. These are intersected by dikes 

 of red syenyte, in part granitic ; these again by others of a quartz-bearing porphyry 

 (orthophyre), greenish, reddish or black, with the crystals of feldspar red; and, 

 finally, there is a fourth series, consisting of grayish-black doleryte, containing some 

 mica, sphene and titanic iron, besides occasionally large crystals of augite. These 

 last resemble the dikes intersecting the Silurian, and are regarded as of Silurian 

 eruption. The others occur where the Laurentian is overlaid by the lowest Silurian, 

 and hence must be of pre-Silurian age. (Logan's Rep. 1863, p. 652.) 



n. Life. 



1. Plants. — No distinct remains of plants have been observed. 



The occurrence of graphite in the rocks, and its making 20 per 

 cent, of some layers, is strong evidence that plants of some kind, if 

 not also animals, were abundant. For graphite is carbon, one of the 

 constituents of wood and animal matters ; and mineral coal, whose 

 vegetable origin is beyond question, has been observed, in the Carbon- 

 iferous rocks of Rhode Island, changed to graphite ; and even coal- 

 plants, as ferns, occur at St. John, New Brunswick, in the state of 

 graphite. Further, the amount of x graphite in the Laurentian rocks 

 is enormous. Dawson observes (taking his facts from Logan) that 

 it is scarcely an exaggeration to maintain that the quantity of carbon 

 in the Laurentian is equal to that in similar areas of the Carbon- 

 iferous system. 



In Europe, graphite occurs in the Archaean rocks of Bavaria; anthracite has been 

 observed in the iron-bearing rocks of this age at Arendal, Norway; and carbonaceous 

 (partly anthracite) and bituminous substances are distributed through layers of 

 Archaean gneiss and mica schist at Nullaberg, in Wermland, Sweden, constituting 

 5 to 10 per cent: facts pointing clearly to the existence of life before the close of 

 this era. 



Animal life, as Hunt observes, may have afforded part of the carbonaceous material, 

 and, perhaps, as large a part as vegetable life. 



The plants must have been the lowest of Cryptogams, or flowerless 

 species, and mainly, at least, marine Algce or Sea-iveeds ; for the Lower 

 bnurian, the next succeeding era, has remains of nothing hisher in 

 its beds. This argument, from the Silurian, excludes all Mosses and 

 the ordinary terrestrial plants ; but not necessarily Lichens, since these 

 grow in dry places, and could not have contributed to marine deposits 



