Geology and Palceontology. 27 



must still remain the reservation that there is room for many- 

 important discoveries in the pre-Cambrian sediments ; and although 

 the contention may be true in the main, we may still find the 

 progenitors of the Cambrian types in pre-Cambrian sediments situated 

 in favourable localities, i.e. as distant as possible from the centre of 

 the pre-Cambrian shield and beyond the limits of the Algonkian 

 continents. 



The present best-known pre-Cambrian fossils are the Beltina of 

 the Belt series, but as an interesting supplement to the recent 

 researches of Professor Garwood on the importance of the work of 

 algae in the formation of the geological record, Walcott describes 

 a series of forms which he compares to the Cyanophyiceae in the 

 limestones of the Belt series and other Algonkian deposits of the 

 Cordilleran region. Apart from these and a few rather doubtful 

 cases, fossils are conspicuously absent in the pre-Cambrian. At the 

 same time a break appears to exist between the pre-Cambrian and 

 Cambrian in Asia, North America, and Europe. In Eastern Asia, as 

 far as the evidence at our disposal will allow us to speculate, north- 

 ward transgressive movements seem to occur in Lower and Middle 

 Cambrian times, the transgression being continued into Upper 

 Cambrian times. A similar set of movements are found in North 

 America with minor oscillations and local regressions in Middle 

 Cambrian times. In Europe there is a suggestion of similar 

 conditions, a basal unconformity, a set of shallow water and laterally 

 varying Lower and Middle Cambrian deposits with abundant non- 

 sequences (some parts of the Middle Cambrian are more extensive 

 and. suggest open waters, but not deep waters), and an important 

 transgression in the Upper Cambrian. Thus the Cambrian period in 

 all three regions represents a time of great oscillatory transgressive 

 movements culminating in the Upper Cambrian, during which the 

 great Algonkian continents were invaded by shallow seas in which 

 marine faunas thrived and multiplied. 



The record of this oscillatory but generally progressive submergence 

 is shown not only by the stratigraphical relationships of the strata, 

 the proved disconformities and overlaps, but appears also in a general 

 survey of the geological provinces of this period. Taking North America 

 and Eastern Asia for example, the Lower Cambrian faunas can be 

 broadly grouped into two main provinces, the North American with 

 Olenellus, etc., and the Eastern Asiatic with its peculiar form 

 Redliehia. In Middle Cambrian times there are again two broad 

 subdivisions, the Pacific and Atlantic, but the dividing line has 

 shifted eastward into the American continent, and the faunas are 

 more varied as a result of the wider extent of shallow seas. During 

 Upper Cambrian times there is a general merging of the various 

 faunas, and the differentiation into provinces becomes indistinct. 

 The history of the faunas is an indication of the history of their 

 habitat, and this Cambrian record indicates the migration and then 

 the breaking down of barriers, the gradual evolution of a narrow 

 strip of shallow seas on the border of large continents, to an epoch of 

 shallow seas and islands, and finally wide marine areas merging and 

 growing around much diminished continental areas. 



