Origin of the- Crystalline JRocA's. 469 



of Pal?eozoic or more recent sediments ; and the other — more ancient 

 — which may be either Neptunean or Plutonic in origin. The history 

 of geology gives many examples of crystalline formations which 

 have been in turn assigned to various geological horizons, from the 

 Cainozoic to the base of the Palceozoic, but have since been found to 

 belong to a pre-Pal?eozoic period. In the opinion of the author, we 

 have no good and sufficient reason for believing in the present 

 existence of any uncrystalline representative of these crystalline 

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

 not pre-Cambrian, in age. There are, however, 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 rocks 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 prevailed 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 crystalline rocks. There have 

 not been wanting those who have sought in similar hypothetical 

 conditions for the origin of these rocks. De 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 1860, to reject the hitherto received view 

 of the epigenic or metasomatic 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 had been " formed by a crystalline molecular re- 

 arrangement of silicates generated by chemical process in waters at 

 the earth's surface." In elucidation of this view the author referred 

 to the insoluble silicates now separated in the evaporation of many 

 natural waters, to the formation from the earliest times to the present 

 of deposits of serpentine, sepiolite, glauconite, and of aluminous 

 silicates allied to chlorite, which are found either forming beds or 

 filling the cavities of various marine organic forms, from the fora- 

 minifers of to-day to the crinoids of Palceozoic time, and the Eozoon 

 of 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 operation which, it is believed, were far more active in 

 Eozoic times. This was not, as had 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 



