MONIAN SYSTEM OF EOCKS. 541 



Is the Monian System Archaean ? This, of course, depends on 

 the definition of Archaean. If we define it as being unfossiliferous, 

 and if I am right in assigning the rocks of Bray Head to it, or if 

 the fossils of Berth Wen are of Monian age, then certainly the system 

 cannot be Archaean. If it is defined as crystalline, then much of the 

 Monian is not crystalline ; nor, for that matter, are the Huronian 

 rocks of Georgian Bay crystalline. If it is not defined, but used 

 simply for " Pre-Cambrian," tlien only are these rocks Archaean. The 

 separation between them and the Cambrian is one of unconformity ; 

 but this unconformity seems scarcely of so great importance as the 

 overlap of the Ordovician. Hence I regard the system as an ordinary 

 stratified system, perhaps fossiliferous on more than one horizon, 

 and constituting the lowest member of the sedimentary series. 

 Towards its base it is metamorphosed, and changes of greater or less 

 amount have passed over every part ; but at their minimum they are 

 no greater, indeed they are less, than in many parts of higher 

 systems ; and these minima occur at nearly every portion of the 

 series. 



Sttbdivisions op the Monian System. 



Although the rocks of the entire system merge one into the other 

 in an imperceptible manner, yet as a sequence may be made out in 

 them, we may usefully divide oif one part from another by artificial 

 lines. We have at the base the grey gneiss, with its episode the 

 quartzites, and then the chloritic and chloritoid schists. The meta- 

 morphosis of these is for the most part nearly complete, though in 

 the two latter there are patches which are in their original state of 

 purple slates. The whole of them are imbedded, except for the 

 bands of grit which here and there occur, and the feeble indications 

 of bedding to be seen at a distance in the quartzites. The chlorites 

 were certainly laminated, and the fine lines in the grey gneiss have 

 probably a similar origin. At all events they are not lines of 

 cleavage, and they are parallel to what, from stratigraphy, in many 

 cases is certainly the surface of deposit. They thus all produce essen- 

 tially lineated rocks, the lines being for the most part also lines of 

 foliation, and under pressure they do not readily fault or cleave, 

 except the quartzites, but crinkle or gnarl. The grey gneiss is 

 felspathic and micaceous, the rest consist of quartz or dust with 

 chlorite or sericite. If a name is required for these we may call 

 them the Holyhead Geotjp (a name unfortunately used before by 

 Dr. Hicks in another sense, as are all the suitable ones), or we may 

 use the term Lower Monian. 



The next succeeding group presents two types. One of these, the 

 most widely spread, is distinguished by the abundance and variety of 

 angular fragments of the rocks, though these are often of minute size. 

 It is also usually marked by want of regularity in the stratification. 

 Nevertheless some parts are thoroughly slaty or gritty, and in others 

 there is no stratification at all. All this is due to the proximity of 

 volcanic centres, which are sometimes indicated by great agglome- 

 rates, sometimes by contemporaneous lava-streams, sometimes by 



