TEE CAMBRIAN PERIOD. 273 



of which Strahan significantly remarks: "They all belong, in part, 

 to the type prevailing in those formations which have been the first 

 to I be deposited at the close of a great continental epoch." 



Recent exploration in China 1 has shown the existence, on the 

 Yang-tse river, in latitude 30°, of a thick formation (170 feet) of bowlder- 

 bearing rock of the typical glacial kind containing many striated 

 bowlders of diverse sorts of rock (Fig. 116a). The striae appear to 

 be of the distinctive glacial type and the matrix in which the striated 

 stones are imbedded is such as bear out the evidence of the stones 

 themselves. The formation lies at the very base of the Paleozoic ter- 

 rane of the region, and beneath the series that carries the Cambrian 

 trilobites. It is therefore to be referred either to very early Cambrian, 

 or to pre-Cambrian time. At present, the most probable interpre- 

 tation is that these formations of Norway and China belong either to 

 the transition period that accompanied and followed the deformation 

 that closed the Proterozoic, or to the opening stages of the Paleozoic 

 previous to the undoubted Cambrian, with some preference for the 

 latter. Whatever their precise age, their profound significance is obvious. 



From Australia 2 and South Africa 3 Cambrian or pre-Cambrian 

 glacial beds have been reported recently. 



In the rocks of undoubted Cambrian age there is little valid evi- 

 dence pointing to diversity of climate. The testimony of the fossils, 

 wherever gathered, implies nearly uniform climatic conditions not only 

 over our own continent, but throughout all the earth where records of 

 the Cambrian period are found. 



Duration of the Cambrian Period. 



There is no way in which a reliable estimate may be made of the 

 duration of the Cambrian period. It is safe to say that the destruction 

 and the removal to the sea of such large volumes of rock as are repre- 

 sented by the sediments of the Cambrian required a very long period 

 of time; but since there is no standard rate at which any sort of sedi- 



1 Willis, Blackwelder, and Sargent. The above note is based on an unpublished 

 oral statement of the results obtained during an extended exploration under the 

 auspices of the Carnegie Institution. See also Year Book No. 3, Carnegie Inst., p. 382. 



2 Howchin and David, Rept. Austral. Assn. for the Adv. of Science, Vol. IX, 1902. 



3 Schwarz, Jour, of Geol.. Vol. XIV, p. 683, 1906. 



