Page:Proceedings of the United States National Museum, Volume 76.djvu/131

Rh The Burgess shale locality in British Columbia, across the Pacific Ocean from Manchuria, is too well known to require any further discussion of its geographic situation.

The third locality is also in British Columbia, but many miles south of Burgess Pass, between Fort Steele and Cranbrook. This locality was first called to the attention of Dr. C. D. Walcott and some of the fossils were collected by Col. H. Pollen, formerly of Fort Steele.

The fourth group of localities is also separated from the two in British Columbia by the width of a continent. The two Pennsylvania localities are only a few miles apart along the strike and hence may be treated as one. Parkers Quarry in Vermont is another place that has been known for many years having become famous when Olenellus thompsoni was described from it. While it has been known for more than thirty years that the Mesonacid fauna was represented in Pennsylvania, it has only been in the last decade that the fauna has become well represented in the collections and the stratigraphic relations of the beds determined.

Relatively large collections, some of them brought together by many years of intensive collecting, are on hand from each of the regions described in the locality lists. Accordingly, we may assume with reasonable confidence that the faunas are fairly represented in our present collections. Yet taking the case of the Burgess shale from which the largest collections (over 35,000 specimens) have been obtained, as an example, we find that in spite of the intensive collecting extending over a number of years, new forms are still found by casual visitors to the outcrop. Strange to relate, all the Tuzoia specimens, except the holotype, turned up only after two full seasons' work. Keeping this example in mind we can the more readily comprehend the likelihood of finding further material at any of the places and thereby alter somewhat our present opinions of the exact composition of the several faunas.

The marvellous preservation of such a host of species in the Burgess shale gives that fauna a definiteness that is scarcely equaled by any other in the entire geologic column, even though its exact stratigraphic position in the Middle Cambrian may not yet be precisely fixed. The Burgess shale has usually been regarded as the exact equivalent of the Ogygopsis shale member of the Stephen formation which like this bed outcrops in only one restricted area—to the south across the Kicking Horse Valley. But a close scrutiny of the apparently identical faunas reveals the fact that many species formerly regarded as common to the two beds are really distinct, thus