444 



NATURE 



\_AugUSt 2 2, 1878 



of altered portions of palaeozoic or more recent sediments, and 

 the other — more ancient — which may be either neptunean or 

 plutonic in origin. The history of j^eology gives many examples 

 of crystalline formations v\ hich have been, in turn, assigned to 

 various geological horizons from the cainozoic to the base of the 

 palaeozoic, but have since been found to belong to a pre-palaeozoic 

 period. In the opinion of the author we have no good and 

 sufficient reason for believing in the present existence of any 

 uncry.italline representative of these crystalline formations, or 

 of any such formation which is not pre-Silurian, if not pre- 

 Cambrian, in age. There are, liowever, many examples of 

 local alterations of later sediments by hydro-thermal action, 

 which has developed in these many crystalline minerals identical 

 with those found in the more ancient rocks. The advocates of 

 the neptunean hypothesis have, for the most part, sought for the 

 origin of the crystalline rocl<s in sediments of a later date, of 

 which the uncrystalline representatives are still to be found. 

 There are, however, reasons for believing that in eozoic, or pre- 

 Cambrian times, there prevailei chemical activities, dependent 

 upon greater subterranean temperature, different atmospheric 

 conditions, and abundance of thermal waters, and that under 

 these circumstances were deposited the materials for the crystal- 

 line rocks. There have net been wanting those who have sought 

 in similar hypothetical conditions for the origin of these rocks, 

 l)e la Beche, in 1834, imagined them to be chemical deposits, due 

 to the action of the heated ocean upon the earth's primeval crust 

 before the dawn of life. 



The author's researches into the composition and structure of 

 the crystalline rocks, conjoined with his studies of the chemistry 

 of natural waters, led him, in i860, to reject the hitherto received 

 view of the epigenic or meta^omatlc origin of serpentine, steatite, 

 chlorite, and similar rocks, and to maintain their derivation from 

 silicates formed by chemical processes and deposited in the water 

 of lakes or seas. This view he soon after extended to the various 

 other exceptional rocks found in crystalline formations, which it 

 was in 1864 asserted, ha'4 been "formed by a crystalline and 

 molecular re-arrangement of silicates generated by chemical 

 processes in waters at the earth's surface," In elucidation of 

 this view the author referred to the insoluble silicates now sepa- 

 rated in the evaporation of many natural waters, to the formation 

 from the earliest times to the present of deposits of serpentine, 

 sepiolile, glauconite, and of aluminous silicates allied to chlorite, 

 which are found either forming beds or filling the cavities of 

 varioxis marine organic forms from the foraminifers of to-day to 

 the crinoids of pala;ozoic time, and the eozoonof the Laurentian. 

 The formation in modern times of crystalline zeolites and quartz 

 in thermal waters was also cited in illustration of this view of the. 

 generation of various mineral silicates by causes now in opera- 

 tion, which, it is believed, were far more active in eozoic 

 times. This was not, as bad been already suggested by, others, 

 a process confined to a seething primeval ocean before the 

 advent of life, but was continued through long ages under 

 varying chemical conditions, and was contemporaneous with 

 the deposition of successive strata of limestone and detrital 

 matters. The argillaceous portions of these, it is con- 

 ceived, may have taken part in the reactions with thermal 

 waters. 



We have thus, in the opinion of the author, a reasonable 

 mode of accounting for the origin of the various rocks of the 

 crystalline formation, and a consistent and complete neptunean 

 theory, which does not invoke the aid of metasomatosis. It 

 has, since it was proposed ei/hteen years ago, met with the 

 approval of many whose studies have made them the fittest 

 judges of its r asonabieness. Among those who have either 

 formally given their adhe; ion to it, or have enunciated similar 

 views, may be mentioned the names of Delesse, Renard» Giimbel, 

 Credner, Alphonse Favre, and Gastakli. 



The chemical activities concerned in the production of the 

 various silicates have doubtless suffered gradual change and 

 diminution through the successive ages of eozoic time, from 

 which have resulted mineralogicil and lithological differences in 

 the crystalline terranes. Eac 1 of these includes quarlzites,and 

 limestones, in which latter certain silicates, such as serpentine, 

 hornblende, and micas, are occasionally found. It is in those 

 aluminiferous rocks, which are without lime or magnesia, that 

 are seen the essential and characteristic differences dependent, 

 as long ago pointed out by the author, upon a decrease in the 

 proportion of alkalis. As we pass from the older to the 

 younger of the eozoic terranes, the feldspar, orthoclase, and 

 albite, become parti^lljt or wholly replaced by silicattjs like 



muscovite, damonite, and paragonite, and finally by andalusite, 

 fibrolite, cyanite, and pyrophyllite. 



The author alluded briefly to the changes by which the ancient 

 a>queous deposits were transformed into crystalline stratified 

 rocks by what Giimbel has de ignated diagenesis, as di>tin- 

 guished from their supposed origin by epigenesis or metaso- 

 matic change. The question of the relation of the indigenous 

 crystalline rocks to tlie endogenous and exotic masses included 

 in them was noticed, the author alluding to the hypothesis which 

 he has elsewhere maintained, that the source of all exotic or 

 eruptive rocks is to be found in the displacement or extravasa- 

 tion of ancient deposits of neptunean origin. 



Coming to the second division of his subject, the author 

 asserted that the study of the crystalline rocks of North America 

 shows the existence of several distinct groups or terraces. 



The Laurentian, which is the most ancient, includes in its 

 lower part a mass of unknown thickness of granitnid gneiss, 

 often hornblendic (Ottawa gneiss), succeeded— perhaps uncon- 

 formably — by what has been called the Grenville series, cm- 

 sisting of similar gneisses and hornblendic rocks with interca- 

 lated quartzites and iron ores. These tvyo divi:-ions maKe up 

 together the lower Laurentian of Logan, of which the thick- 

 ness in Canada may greatly exceed 20,000 feet. 



The Norian, which is the upper Laurentian or Labradorian 

 of Logan, rests unconformably upon the Laurentian, and is re- 

 markable for a great development of rocks composed chiefly of 

 labradonte or related plagiuclase feldspars, whiph have bf-en 

 called labradorite-rock or norite. The interstratified gnei ses, 

 i quartzites, and limestones of the Norian are not unlike those 

 of the Laurentian, 'I his series, which abounds ip great b<rds 

 of titanic iron-ore, has a great volume which may exceed the 

 thickness of 10,000 feet assigned t ) it by Logan, 



The Laurentian is in many parts unconformably overlaid by 

 the Huronian series, which is characterised by a great develop- 

 ment of greenstone--, generally hornblendic, with epidote, 

 chlorite, steatite, serpentine, and soft hydrous mica-schists, often 

 called talcoe, besides argillites, quartzites, and limestones, 

 generally magnesian. It abounds in metalliferous deposits, in- 

 cluding magnetic and specular iron-ores, chrome, and sulphurets 

 of copper, iron, and nickel, and has had assigned to it in differ- 

 ent regions a thickness of from ten to twenty thousand feet. 



In many parts of North America there exists a great develop- 

 ment of rocks characterised by the predominance of orthofelsite 

 or petrosilex, often becoming a quartziferous porphyry. This, 

 which is ap] arently the hdlleflinta of Sweden, was regarded as 

 eruptive until, in 1869, the author show ed it to be a stratified 

 series with some associated quartzites and schists, and then in- 

 cluded, it in the lower part of the Huronian. Hitchcock, who 

 has since studied these rocks in New Hampshire, has called 

 them lower Huronian, From their absence in many localities 

 at the base of the typical Huronian, it is conjectured that they 

 may belong to a ri^ore ancient and distinct series. 



The Mpntalban or White Mountain series is characterised by 

 micaceous gneisses, generally called granites, which pass into 

 quartzose and feldspathic mica-schists, often abounding in garnet, 

 staurolite, fibrolite, and cyanite. Great masses of dark green 

 gneissoid hornlJendic rock, very distiixct fronj the Huronian 

 greenstones, abound in the Montalban, which also includes beds 

 of a peculiar olivine rock, besides quartzites and crystalline 

 limestones. This series abounds in endogenous granitic veins, 

 containing muscovite, beryl, tourmaline, apatite, and oxide of 

 tin. It probably equals the Huronian in thickness, and is sup- 

 posed to overlie it. 



The Taconian series includes a great volume of characteristic 

 mica-schists, often quartzose, but seldom distinctly feldspathic, 

 and frequently con-i ting in large part of damonite, or of pyro- 

 phyllite. Some of the-e, like the schists of the Montalban, 

 include garnet and chia-tolite, Tliey are associated with 

 quartzi'es and with dolomites and limestones, all of which are 

 also frequently micaceous. Associated with these are found 

 serpentines and granular hornblendic rocks of a peculiar type, 

 very unlike those of the preceding groups and much less crystal- 

 line. The quartzites are in large part detrital rocks. This 

 series, which yields the statuary marbles of North America, has 

 a thickness of about 5, coo feet and is the lower Taconic of 

 Emmons. It is found i-eposing alike on the Laurentian, Hu- 

 ronian, and Montallian, and is overlaid, in apparent uncon- 

 formity, by the upper Taconic, which is identical with the 

 Quebec group of Logan. Thi^--, which consists of many thousand 

 feet of sandstones and argillites, with some limestones, includes 



