Page:Walcott Cambrian Geology and Paleontology II.djvu/18

 1891a, pp. 594-595] I said, when speaking of the "Origin of Fauna":

If we attempt to classify the Olenellus fauna by its genesis, an almost impenetrable wall confronts us. That the life in the pre-Olenellus seas was large and varied there can be little, if any, doubt. The few traces known of it prove little of its character, but they prove that life existed in a period far preceding Lower Cambrian time, and they foster the hope that it is only a question of search and favorable conditions to discover it. As far as known to me, the most promising area in which to search for the pre-Olenellus fauna is on the western side of the Rocky Mountains in the United States and on their eastern (western) slopes in British Columbia. There the great thickness of conformable pre-Olenellus zone strata presents a most tempting field for the student collector. Another of the known possible areas is that of New York and Vermont, but the prospect is not as favorable as in the West. Other and better fields may exist in Asia and Africa, but as yet they are unknown, with the exception of the areas described by Baron Richthofen in China [Richthofen, 1882, Vol. 2, pp. 94, 100, and 101] where a great thickness of conformable sedimentary beds exists beneath a horizon that is comparable with the Middle Cambrian of western North America.

With the above thought in mind I have for the past eighteen years watched for geological and paleontological evidence that might aid in solving the problem of pre-Cambrian life. The great series of Cambrian and pre-Cambrian strata in eastern North America from Alabama to Labrador; in western North America from Nevada and California far into Alberta and British Columbia, and also in China, have been studied and searched for evidences of life until the conclusion has gradually been forced upon me that on the North American Continent we have no known pre-Cambrian marine deposits containing traces of organic remains, and that the abrupt appearance of the Cambrian fauna results from geological and not from biotic conditions. I do not mean by this to infer that Brooks' hypothesis [Brooks, 1894, pp. 455-479] of the origin of the earlier forms of life in the surface waters of the open ocean is incorrect, but I mean that we have no known record in the strata of the marine life of the period between those earlier open-sea forms and the first records of life found in the Lower Cambrian strata. That such life existed there can be no question. It is the imperfection of the geological record as known to us that is the cause of the present uncertainty as to the pre-Cambrian faunas, and the abrupt appearance of the Cambrian fauna.

It is my present view that the known later Algonkian rocks