October 29, 1915] 



SCIENCE 



613 



large and spiny shells. The original type of 

 snails followed the " young " part of the stream 

 backward and thus there tends to be a continu- 

 ous series of forms as one follows the stream. 

 One has but to start at the headwaters and go 

 down stream in order to see unfolded the his- 

 tory of both stream and shell. By the time 

 Chattanooga is reached the stream has gotten 

 too old, physiographically, for the snails, too 

 deep and possibly too contaminated. 



The finding of smooth shells near Eogers- 

 ville in the Holston Eiver and of spiny shells 

 above them really fits in with this idea if we 

 look more closely into the history of this part 

 of the river system, for here there has been 

 stream piracy. A young stream containing 

 smooth shells has probably worked over into 

 the valley of an old stream, containing spiny 

 shells above the point of intersection, and the 

 result is the Holston River as we now know it. 



To be sure, we should like to have an ex- 

 planation of the causes underlying the law of 

 ornamentation, and also of the reason why the 

 successively spinier snails seem to have forced 

 their smoother relatives to migrate with the 

 growth of the stream or to have been prevented 

 from working up to the headwaters themselves, 

 but we can not expect an explanation of the 

 ultimate and Dr. Adams is to be congratulated 

 on the progress which this paper makes in the, 

 as yet, largely unexplored field of animal 

 ecology. Frank E. Lutz 



THE PLIOCENE FLOBAS OF HOLLAND 

 The study of the more immediate progen- 

 itors of the existing flora, the vast changes in 

 distribution, and the extensive extinctions and 

 migrations that resulted from the glaciation 

 of the Pleistocene, as well as the evolution of 

 recent herbaceous forms that followed in its 

 wake, constitutes a field of endeavor that not 

 only appeals to the imagination, but one that 

 offers much to botany and much that is useful 

 in reconstructing the geography, climate and 

 history of the late Tertiary and the Quaternary. 

 For thirty-odd years Clement Eeid has been 

 engaged in the study of the Pliocene and 

 Pleistocene deposits of Britain and their con- 



tained floras. Some years ago with the assist- 

 ance of Eleanor M. Eeid he described the upper 

 Pliocene flora of Tegelen in Holland, "^ and 

 recently these authors have published the re- 

 sults of an elaborate study of similar remains 

 from a slightly older horizon collected from the 

 brick-clays of Eeuver, Swalmen and Brunssum 

 along the Dutch-Prussian border.^ 



This study is not only a significant contribu- 

 tion to the botany of the Pliocene, but it fur- 

 nishes data of great importance to historical 

 geology. With the shallowing of the Diestian 

 or perhaps the Scaldisian sea, the delta of the 

 combined Rhine and Meuse extended a long 

 distance to the northwest as it did at several 

 subsequent times during its history, as is 

 proven by the Ehine gravels in the Cromer beds 

 of Norfolk, and by the mammalian fauna and 

 peat of the Dogger Bank. Remains of the 

 middle Pliocene high-level terraces, much 

 faulted, occur to the south and east of the 

 Limburg plain, where the brick clays are ex- 

 posed in the scarp facing that plain. The 

 materials were collected by W. Jongmans of 

 Leiden and P. Tesch of the Geological Insti- 

 tute for the exploration of the Netherlands. 

 The Eeids expended all of their efforts on the 

 remains of fruits and seeds which they labori- 

 ously picked out of the washings of an enor- 

 mous amount of material. 



In the less lignitic loams lying immediately 

 below the horizon reported upon, impressions 

 of leaves occur and these were studied some 



lEeid, C, and E. M., "The Fossil Flora of 

 Tegelen-sur-Meuse, near Venloo, in the Province 

 of Limburg," Verhandl. Kon. Akad. Wetensch. 

 (Tweede Seotie), Eeel XIII., No. 6, 1907; "On 

 DuUcliium vespiforme sp. nov. from the Brick- 

 earth of Tegelen," Verslag. Kon. AJcad. Wetensch. 

 Amsterdam, 1908, p. 898; "A Further Investiga- 

 tion of the Pliocene Flora of Tegelen," Ibidem, 

 1910, pp. 192-199. 



■2 Eeid, C, and E. M., "Preliminary Note on 

 the Fossil Plants from Eeuver, Brunssum and 

 Swalmen," Tijdsch. Kon. Ned. Aardrijlcs. Geno- 

 otschap, 2e ser., Deel XXVIII., afl. 4, 1911, pp. 

 645-647; "The Pliocene Floras of the Dutch- 

 Prussian Border, ' ' Mededeelingen SijTiSopsporing 

 van Velfstoffen, No. 6, The Hague, 1915, 178 pp., 

 4 tf., 20 pis. 



