so ROYAL SOCIETY OF CANADA 



while irregularly disposed among these are schistose rocks of imcertam 

 age. It was at one time supposed that all these schistose and felspathic 

 rocks were of Pre-Cambrian age, and they were thus represented in the 

 geological survey maps, but more recent investigation, both in the field 

 and with the microscope, have clearly shown, as regards the felsitic rocks 

 'at least, that these are really much more recent, representing rhyolitic 

 overflows which may be as recent as Silurian or even Devonian. The 

 region is everywhere hilly and often mountainous, but, as in the case of 

 the plateau which borders it on the north, what from the valleys appear 

 to be mountains are' only the dissected ends of ridges, all of which may be 

 fragments of what was once a nearly uniform plateau. In addition to 

 the marked difference of elevation between this plateau and that last 

 described it may be noted that the transition from one to the other is 

 often quite abrupt, and that along the line of separation there are evi- 

 dences of extensive dislocations. 



(5) The Central or York County Plateau. — This is composed al- 

 most solely of alternating slates and quartzites, all of which in early re- 

 ports were referred to the Quebec Group and believed to be of Cambrian 

 age. But though at a few points strata embracing upper Cambrian or 

 Cambro Silurian fossils have been met with, others carrying a fauna 

 which is near the transition from Silurian to Devonian "have also been 

 recognized, and are so distributed at widely separated points as to justify 

 the belief that the great bulk of the strata are to be referred to the latter 

 horizon. Here again it has been found impossible as a rule to distin- 

 guish crustal movements on a large scale, the strata as exhibited in river 

 sections showing rather a repeated succession of minor folds and irre- 

 gularly crumpled beds, with occasional outcrops of granites or other in- 

 trusive masses. In places the slates and quartzites are unconformably 

 covered by small areas of Devonian, Lower Carboniferous and Carboni- 

 ferous rocks. 



(6) The Central Basin. — This is almost wholly occupied by Car- 

 boniferous rocks, representative mainly of the Millstone Grit formation, 

 but bordered by narrow belts of Devonian ( ?) and Lower Carboniferous 

 rocks, which also are occasionally laid bare in its interior. With the 

 Devonian (?) and Lower Carboniferous rocks which consist mainly of 

 conglomerates and sandstones, easily distinguished by their bright colour 

 and highly calcareous character, determining very productive soils, in- 

 trusions and overflows of volcanic rock, in some instances basic and in 

 others acidic, are met with, and occasionally rise into prominent hills. 

 The Millstone Grit or Coal measure rocks on the other hand exhibit few 

 inequalities except such as are due to fluviatile erosion, and over very- 

 extensive areas form a surface which is flat or only slightly undulating. 



