THE NATURAL HISTORY OF IGNEOUS ROCKS. 15 



Bertrand and many others has now given us a sufficient 

 general idea of the nature, situations and epochs of the 

 most important crust-movements during- the times contem- 

 plated by the stratigraphical geologist, and it is possible to 

 discuss to some extent the relation to these movements of 

 the known groups of igneous rocks, both intrusive and 

 extrusive. This has been done summarily for the European 

 area by Bertrand in a memoir, published in 1888, which 

 may be taken as a model for this kind of investigation (2). In 

 a more restricted region, the geological history of which is 

 sufficiently well known, the comparison may be developed 

 in greater detail. For an application to our own country 

 the data are furnished by Sir A. Geikie's account of volcanic 

 action within the British area, contained in his Presidential 

 Addresses to the Geological Society in 1891-92, and 

 supplemented, as regards the Tertiary igneous rocks, by 

 his memoir of 1888 [Travis. Roy. Soc. Edin.), and by 

 the various papers of Judd. 



Bertrand distinguishes in Europe four great systems of 

 folding and disturbance of the stratified rocks; the earliest, the 

 so-called Huronian, being here added to the Caledonian, 

 Hercynian, and Alpine systems already recognised. The 

 regions affected by these disturbances form broad zones, 

 limited on the map by sweeping curves ; and the several 

 zones, while partially overlapping one another, successively 

 advance further towards the equator. It seems probable 

 that the first, and perhaps also the last, of these four 

 systems must eventually be further divided, but Bertrand's 

 statement of the broad facts affords meanwhile a basis for 

 important generalisations. To the Huronian system belong 

 crust-movements of pre- Palaeozoic and early Palaeozoic age, 

 the first efiects of which are seen in the north-western 

 Highlands of Scotland and along the Norwegian coast, 

 though the region ultimately involved had a considerably 

 wider extent. The Caledonian (Upper Palaeozoic) dis- 

 turbances affected the greater part of what are now the 

 British Isles as well as a belt extending north-eastward 

 through Scandinavia. The main zone of Hercynian fold- 

 ing, marking the close of Palaezoic time, extends eastward 



