Page:The Journal of geology (IA journalofgeology21894univers).pdf/123

Ells^[2] gives a description of the Laurentian of the Ottawa district. A reëxamination of the Trembling Mountain section shows that, instead of its being a continuous ascending series, there are no less than three anticlines and their corresponding synclines, and the section is still further complicated by faults of every considerable extent. But one limestone was found, that of Trembling Lake, and this instead of being interstratified with the orthoclase gneiss is in the form of a synclinal overlying this gneiss. This limestone at no point was observed to be more than 50 feet in vertical thickness.

In the region between the anorthosite area and the Gatineau river the limestone in nearly every case occupies well defined synclinals separated by anticlinals of the underlying gneiss. In this area it has been found impossible to trace any bands of limestone to any considerable distance continuously, the limestones being often local in their development, and lenticular in form.

In the limestone in certain places are masses of quartzose rock and crushed gneiss, presenting the aspect of a true conglomerate. As to the thickness of the gneiss, on the Rouge river, the most favorable place found for measurement, the section gave a thickness of 10,000 feet beneath the limestone, if there is no break, but this figure may not be accurate, as faults and repetitions of strata may occur at several places.

Intrusive within the gneiss and limestone are the anorthosite and syenite masses of Grenville and Chatham, and other less conspicuous masses. No less than six or seven clearly distinguished periods of intrusion can be recognized. The augen gneiss of the Rouge river is probably also an intrusive.