VALUE OF FLORAL EVIDENCE 221 



VALUE OF FLORAL EVIDENCE IN MARINE STRATA AS INDICATIVE OF 

 NEARNESS OF SHORES^ 



BY DAVID WHITE 



In discussing, from the paleogeographic standpoint, the occurrence of 

 plants in limestones or other marine sediments primary consideration 

 must scrupulously be given, first, to the kind of plants, and, second, to 

 the condition of the plants. 



In illustration of the first of these considerations it is hardly necessary 

 to remark that algae of marine types, though they may be blown along 

 the beach and into coastwise dunes, are not likely to find a place in epi- 

 continental fresh-water basins nor, except in the rarest instances, in 

 eolian desert deposits. Neither, on the contrary, should one look in 

 fresh-water coal basins for salt-marsh vegetation. So, also, though he 

 may discover fresh-water limestones, which directly owe their very being 

 to fresh-water algae, one should not expect to find sweet-water thallo- 

 phytes composing limestones in a marine environment. Each limestone 

 contains calcareous or other algae of its own kind. Otherwise do "men 

 gather figs of thistles." 



In practice, however, and for general paleogeographic uses algae are 

 apt to be of little need, or if needed they frequently are of little help, so 

 very imperfect is our paleontologic knowledge of the small calcareous 

 rock-building types, and so poorly preserved are usually the others 

 whether in rocks of organic or terrigenous origin. Therefore, in the 

 present discussion, further consideration will be confined to land plants ; 

 and, since the question is one of geographic values, to vascular only. 

 This brings us, in our weighing of fossil plant criteria, to the second 

 important point, namely, the condition of the plants themselves. 



The occurrence of remains of land plants in limestone is uncommon 

 enough always to attract the attention of the geologist, but the discovery 

 of well preserved specimens, especially leaves, in a limestone formation is 

 so exceedingly rare as never to fail to excite comment. In fact finding 

 good specimens of land plants in the company of marine invertebrates in 

 any place is worthy of mention, regardless of the sedimentary circum- 

 stances. 



It is worth while in this connection to give brief attention to the con- 

 ditions now to be observed and the processes now in operation in the seas 

 of the present day. The reports of the Blake, the Challenger, and the 



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



