EVIDENCES OF PRIMITIVE LIFE WALCOTT. 253 



Canada has recently held its siunnier camp on the shores of Berg 

 Lake, and soon this wonderland will be open to all who love the 

 mountains and outdoor life. 



Some of the fossil trilobites of this region are illustrated on plate 

 17 {Olenellus trucmani Walcott, figs. 2-10)/ and may be correlated 

 Avith another similar species (pi. 14, fig. 9, Olenellus thoTnpsoni 

 (Hall)) from a Lower Cambrian shale in Pennsylvania and other 

 Appalachian localities. Often the discovery of these correlations 

 proves of great importance in the assignment of strata to their proper 

 formations, and it has frequently been of great service in prospecting 

 and exploiting mining districts in the West and elsewhere. A fault 

 or break in the strata is sometimes detected only by this means. 



UPPER CAMBRIAN FAUNA OF THE IMISSISSIPPI VALLEY. 



The importance of the distribution of a single family or genus in 

 determining the stratigraphic position and succession of layers is 

 sliow^n in a recent study of the Dikelocephalinas ^ (pi. 18). 



It had been evident for several years that the various Cambrian 

 formations of the Upper Mississippi Valley, which had been re- 

 ferred first to one formation (Potsdam) and then to another (St. 

 Croix sandstones), needed careful revision in relation to their 

 stratigraphic position and succession. This was accomplished 

 through the study of the distribution of the JJ'ikelocephalus ^ fauna 

 in this wide region, and its correlation wdth related genera and 

 species elsewhere. 



THE SARDINIAN CAMBRIAN GENUS OLENOPSIS IN AMERICA.* 



An example of the significance of distribution in showing unsus- 

 pected relationship of widely separated faunas, and consequently a 

 bond between the marine bodies of water which covered the land 

 at an early age, is found in the study of the geographic distribution 

 of a remarkable trilobite. Until the publication of the report in 

 1912 the presence of the genus Olenopsis in America had not been 

 announced, although a number of the cranidia of species referred 

 to the related Ptychoparla were very much like the cranidia of 

 Olenopsis. 



The type species, Olenopsis zoppii, occurs on the island of Sar- 

 dinia at Canal Grande and vicinity. Investigation in North America 



1 Fig. 1 on this plate represents a related species, ITolmia ? macer Walcott, from the 

 Lower Cambrian shale, Fruitville, Lancaster County, Pennsylvania. 



2 Walcott : Dikeloceplialus and other genera of the Dikelocephalinas. Smithsonian Misc. 

 Coll., vo: 57, no. 13, 1914. 



^Dikeloceplialus, a large trilobite characteristic of the later (Upper) Cambrian rocks. 

 Dikeloceplialus, from Greek SiKcXXa, a mattock or two-pronged hoe. and K€<t,a\e head. 

 This trilobite has been called " shovel-head," well suggested by fig. 1, pi. 18. 

 * Walcott, Smithsonian Misc. Coll., vol. 57, no. 8, 1012. 



