56 



sediments had been derived. The Huronian conglomerates, however, 

 hold no pebbles that are undeniably referable to the Laurentian, and 

 the origin of the syenitic, quartzose and jaspery pebbles is still a matter 

 of doubt. The microscope can throw no certain light on the original 

 character of some of these rocks, for very often metamorphism and 

 recrystallization has gone on to such an extent that the former structure 

 has been either partially or completely obliterated. A close study of 

 these uncertain rocks in the field, aided by the use of the microscope 

 in the laboratory will eventually enable us to assign them their proper 

 place. We have thus numerous sedimentary rocks showing the various 

 stages of this metamorphism, from the typical sandstone or greywacke, 

 composed of well rounded grains of quartz and felspar, to the compact 

 felsite, which contains no trace of its original clastic structure. Associ- 

 ated with these sedimentary strata are certain undoubted eruptive and 

 irruptive rocks, among which may be mentioned many varieties of 

 diabase; diorite and gabbro. Besides these igneous rocks, there are 

 some granites and gneisses concerning whose origin many are in doubt. 

 After a close and careful study of these rocks, which have usually been 

 classified as Laurentian, and their relations with the true Huronian 

 stratified deposits, I have been fully convinced of their irruptive nature. 

 These granites and gneisses probably represent the original crust of the 

 earth which has undergone refusion, and was in a molten or plastic con- 

 dition at a period subsequent to the hardening of the Huronian sedi- 

 ments. The earth gradually cooling from a state of original incan- 

 descence, had reached that stage in the process when it admitted of 

 being surrounded by an ocean nearly, if not quite, universal. Then 

 began that tearing down and building up which has since gone on in 

 forming the sediments which subsequently hardened into rocks. The 

 first formed crust was necessarily thin and weak, and it is therefore not 

 surprising that there were frequent irruptions, accompanied by the 

 fusion of the lower portion at least of the first formed deposits. 



It is unnecessary here to go into all the facts of the case, as my 

 riews have already been stated at some length in a paper read before 

 this club on February 27th of last year. Suffice it to say that the fuller 

 examinations of last summer have served to further strengthen these 

 views. Both clastic and irruptive rocks have been subjected to in- 



