358 SCIENCE PROGRESS. 



west Highlands amongst those rocks which he claimed as 

 largely Precambrian, and to which he gave the name Dal- 

 radian. Similar sediments have been proved of Precam- 

 brian age in many extra- British areas, our knowledge of 

 them in America being fairly extensive, owing to the recent 

 work of Van Hise, Lawson, Irving, Walcott and others. 

 In America, as in Britain, chronological classification cannot 

 be carried very far at present, and the majority of American 

 writers are satisfied with separating undoubtedly bedded 

 Precambrian rocks, under the name of Algonkian, from 

 those of igneous and doubtful origin, for which they retain 

 the name Archaean. An admirable summary of the present 

 knowledge of these American rocks has been recently given 

 by Van Hise (4). Further consideration of the Precambrian 

 rocks may be deferred until we consider, in the latter part 

 of this article, the application of our knowledge of strati- 

 graphical principles. 



2. THE CAMBRIAN SYSTEM. 



The establishment of the position of the Olenellus zone 

 by Nathorst (5), Brogger (6) and others has given us a satisfac- 

 tory base to the strata appertaining to the Cambrian system, 

 and the sequence of Cambrian faunas is now firmly estab- 

 lished. It is generally admitted that the Olenellus, Para- 

 doxides and Olenus faunas succeed each other in definite 

 sequence, and the only want of accordance amongst geolo- 

 gists concerning the rocks of this system is on a matter 

 of classification, the foreign geologists placing the beds 

 with the Tremadoc fauna in the succeeding system, whilst 

 British geologists relegate them to the Cambrian. As the 

 fauna constitutes a true passage between those of the Cam- 

 brian and Ordovician systems, the question is one of small 

 importance. Undoubtedly, the greatest advance in our 

 knowledge of the rocks of the Cambrian system of recent 

 years is due to the detection of the Olenellus beds in widely 

 remote regions. The splendid monograph upon these beds 

 by Walcott (7) contains a bibliography up to the year 1890. 



