WALC0TT.1 PROBLEMS FOR INVESTIGATION. 387 



extension of this fauna in the series of shales, slates, and sandstones 

 beneath the now known Olenellus horizon of the western Rocky Moun- 

 tain Province. The lower series of slates and quartzites have been 

 tentatively referred to the Algoukian, but it is quite probable that 

 they will be found to carry the Olenellus fauna to a considerable depth, 

 and a pre-Olenellus fauna may yet be discovered. 



The problem of the downward extension of the Cambrian faunas also 

 requires investigation in the Appalachian Province, especially in the 

 southern portion — in Tennessee, Georgia, and Alabama. The basal 

 limit of the Cambrian is now drawn at the Olenellus zone, but in the 

 absence of any subjacent fauua there still remain the problems of the 

 downward extension of the Cambrian fauna and of the existence of a 

 pre-Cambrian fauna that may have lived in the Appalachian seas. 



A local question of interest may be here introduced, as it affects a 

 considerable area and involves conditions of sedimentation unknown 

 elsewhere in the Cambrian. It is the question of the place of deriva- 

 tion and mode of transportation of the bowlders of the limestone con- 

 glomerates that carry in the lower zone, the Lower Cambrian, and in the 

 upper zone the Upper Cambrian fauna found along the southern shore 

 of the St. Lawrence River from Quebec to Gaspe. 



One of the problems partially solved, and one that still requires in- 

 vestigation, is the relation of the pre-Cambrian topography to the sedi- 

 ments deposited upon it, to determine the source of sediments and the 

 habitat of the faunas. 



Along the Atlantic coast the presence of the pre-Cambrian shore line 

 with a varied coast topography is clearly distinguishable, and it is evi- 

 dent that the Cambrian strata now occupy the same relative position to 

 the pre-Cambrian as the sediments did when they were deposited. The 

 same is true of the shore-line deposits along the western margin of the 

 Appalachian, pre-Cambrian protaxis, and the sediments about the Adi- 

 rondack area. Between the Adirondacks and the Green Mountains a 

 great thickness of Cambrian rocks appears to have been deposited in a 

 deep, relatively narrow sea; but what the conditions were to the west- 

 ward of the long line of the eastern boundary of the Appalachian Prov- 

 ince is one of the questions requiring solution. The same is true of the 

 western limits of the sediments now exposed in the great uplifts of 

 central Nevada and British Columbia. 



The questions arising from the study and comparison of the various 

 provinces all require a more thorough investigation of the sections of 

 the western Rocky Mountain, Appalachian and Atlantic Coast Prov- 

 inces. They bear upon the nomenclature and classification to be adopted 

 for the Cambrian group ; and not until we have a more thorough knowl- 

 edge of the sections of northern Vermont, New York, Tennesse, British 

 Columbia, and Nevada can the classification be considered more than a 

 provisional one. 



