368 SCIENCE PROGRESS. 



zones in Scandinavia, a full account of which appears in 

 Tullberg's paper on the graptolites of Scania (20), one of 

 the most valuable of recent contributions to the literature of 

 the graptolites. Tornquist, Perner, Barrois and others 

 have also identified various graptolitic zones in Thuringia, 

 Bohemia and France. In North America the principal 

 contribution is by our own countryman, Lapworth, who has 

 identified a number of graptolite zones in Canada, which 

 are identical with those detected in Europe (21). In 

 Australia T. S. Hall is studying the well-known Areing 

 graptolite fauna, and finds that the graptolites here also are 

 limited to special zones (22). A number of other papers 

 might be quoted to show the general recognition of the 

 utility of graptolites for purposes of correlation of strata, 

 but enough has been said to indicate the manner in which 

 the work is progressing, and the vast amount which yet 

 remains to be done in this connection. I cannot leave this 

 part of the subject without uttering a warning note. More 

 harm is done by a wrong determination than good by a 

 correct one. The graptolites are by no means easy of 

 identification by those who have not made them a special 

 study, and it is particularly desirable that no determination 

 should be recorded by tyros, unless it is absolutely certain, 

 for when once a wrong name has crept into a list it is 

 exceedingly difficult to remove it. I could give several 

 instances of very serious mistakes of this kind which have 

 been made, each of which will have to be corrected else- 

 where, but it would be invidious to give names in a 

 general article of this character. 



We may now pass on to consider the physical conditions 

 under which the graptolite-bearing strata were deposited. 

 There is very little doubt that they were formed in water of 

 very different degrees of depth, for graptolites are found in 

 arenaceous, argillaceous and calcareous strata. Thev have 

 mainly been collected from deposits which there is every 

 reason to suppose were formed in deep seas, because a much 

 greater number of individuals occur in a given space under 

 such conditions than when the deposits were formed rapidly. 

 The writer has elsewhere given cases of graptolitic deposits 



