How Rocks are Formed. 165 



associations of many of these deposits with clearly intrusive rocks that 

 their origin is more closely related to these latter than to any organic 

 agencies as is the case with the recent iron ore deposits. 



Of late years the microscope has come to the aid of the field 

 geologist and has been of wonderful assistance in solving the problem 

 pertaining to the structure and origin of many rocks, concerning 

 whose genesis much doubt had long existed. By the increased light 

 thus furnished, many new facts have been adduced which have, on 

 certain lines, almost entirely revolutionized our earlier ideas as to rock 

 structure and by the union of the forces of the field and the laboratory 

 much more satisfactory conclusions have been reached, It may be 

 safely said that by this means, the progress in accurate geological 

 investigations during the last ten years has been far greater than in any 

 previous similar period, and the results obtained have been much more 

 reliable. 



The vicinity of Ottawa is excellently adopted for the study of many 

 rock formations. Along the line of the Gatineau railway many beauti- 

 ful sections of the early crust are exposed in the form of granite, gneiss 

 and crystalline limestone, and their intersections by dyke-like masses of 

 deeper seated rocks are well seen, as syenites, diorites, pyroxenes, felspars, 

 etc. The Ottawa, Arnprior and Parry Sound and the Canada Atlantic Rail- 

 ways both traverse areas occupied by the lower Palaeozoic rocks and many 

 instructive outcrops of sandstone, shale and limestone are easily avail- 

 able to the geological student. Some of the strata of the Chazy and 

 Trenton are wonderfully rich in organic remains. The former of these 

 two great rock divisions illustrate the conditions which prevailed when 

 the earliest ocean waves dashed against the oldest outlines of our con- 

 tinent, and strewed the debris of sand and pebbles throughout the 

 Ottawa area, while the limestones and shales of the Chazy and Trenton 

 show the prevalence of deeper water conditions and ihe abundance of 

 the animal life even in those early days of the world's history. The 

 most recent deposits of clays, sands and gravels can also be studied at 

 many points along the river Ottawa as well as over the country adjacent 

 on either side, and their contained organisms, in the shape of bones of 

 seals and fishes, as well as marine shells, are familiar to many of the 



