Page:Walcott Cambrian Geology and Paleontology II.djvu/234

 the phyllopod bed, as it contains a large, unique, and fine series of phyllopod remains. It has a thickness of 7 feet, 7 inches, and is capped by a layer of coarse, bluish, dirty-gray shale weathering to a yellowish ochre-brown on the edges, that averages 18 inches in thickness. The phyllopod bed may be subdivided as follows from the top downward:

Below No. 12 the layers of shale are arenaceous, irregular, and not favorable for preserving fine fossils.

In making the collections of 1910 and 1911 over 150 cubic yards of rock were quarried and split up. Frequently, however, many square feet of surface of the shale would be opened without exposing a desirable specimen.

Layer No. 12 is of great interest. It was a slab of this carried down by a snow slide that Mrs. Walcott and I found in 1909 on the trail from Burgess Pass to Summit Lake. It contains Marrella splendens in great numbers, and of the annelids it has yielded the only specimens of Miskoia preciosa and Amiskwia sagittiformis, and most of those of Pikaia gracilens, Wiwaxia corrugata, and Canadia spinosa. Among the crustaceans the only specimens of Opabinia regalis, Molaria spinifera, Yohoia tenuis, Y. plena, Mollisonia gracilis, and M. ? rara were found in it, and Burgessia bella, Waptia