VALUE OF FLORAL EVIDENCE 227 



writer's opinion, the examples cited not only point out movements which 

 may subdivide Mississippian time, but they also lend support to the views 

 of Ulrich as to the shallowness of the Mississippian seas. 



In the abundant and familiar cases of the association of finely pre- 

 served leaves and fern fronds with marine shells in the roofs of coals in 

 all the epochs of vascular land plant life, Paleozoic, Mesozoic, Cenozoic, 

 and Eecent, and in various regions of the world, the coals and their 

 underlying old soils bear witness to their paleogeographic relations as 

 coastal or lagoonal swamps which at the moment of molluscan invasion 

 had just been inundated by the sea.^^ 



The deductions drawn from the occurrence and conditions of land plant 

 material in the oceanic areas of today and from the stratigraphic relations 

 and state of the corresponding fossils found in the older deposits, appear 

 fully to justify the conclusion that the presence of clean and well pre- 

 served leaf material in limestones or other marine sediments constitutes 

 satisfactory proof of proximity of the deposit to land; as, conversely, the 

 occurrence of water-worn, partially decayed, incrusted, or corroded ma- 

 terial permits the conclusion that the specimens may have been for some 

 time in water and are therefore liable to have been transported for some 

 distance. Unfortunately, the evidence of fossil plants, though of the 

 highest value in paleogeographic deductions, is so rare as usually to be 

 wanting on the occasions of greatest need. 



ARE THE FOSSILS OF THE DOLOMITES INDICATIVE OF SHALLOW, HIGHLY 

 SALINE AND WARM WATER SEAS?^ 



BY STUART WELLER 



It must be recognized at the outset, in the discussion of the subject 

 which has been assigned me, that all dolomitic formations have not been 

 deposited under like conditions. In such magnesian beds as are present 

 in the Cayugan period of the Silurian, we find a most peculiar fauna, 

 constituted almost wholly of the strange Eurypteroid arthropods whose 

 fossil remains are almost never found in association with typical marine 

 faunas, but which are present in situations, such, for instance, as the 

 plant-bearing beds of the Pennsylvanian, which indicate that they must 

 have lived in non-marine waters. The stratigraphic association of these 

 Cayugan, Eurypterus-bearing beds with beds of salt and gypsum would 



1 Manuscript received by tlie Secretary of the Society May 23, 1911. 

 " The plant-bearing limestones of the Purbeck on the Dorset coast lie on the dirt beds 

 (old soils), on which the vegetation grew. 



