The Yorkshire Jurassic flora

THE YORKSHIRE JURASSIC FLORA the Yorkshire compressions were 'impressions with carbon'; he knew cuticles were present, for he prepared the cuticle of Solenites as Murray had done seventy years before, but he did not know that such a preparation could be valuable.He also followed the normal tradition in limiting his work to the description of specimens amassed by geologists.As far as I can tell, he collected only one specimen (from Whitby).Nathorst visited England to study this flora, in the field and in Museums, well before this (1880), but it was only after 1900 that his work and influence became important.It w T as then that he prepared and described cuticles (for example from Williamsonici flowers) which he and his colleague, Halle, had collected ; the preparation of such cuticles was not new, the new idea was that their microscopic study was of interest and use.Once the microscope could be used fully, 'impressions' ceased to be automatically inferior to 'petrifactions', and two vitally important results followed.The reproductive organ (often inconspicuous) became of supreme importance and the large slabs of foliage, sought for in particular by the professional collector became inadequate.Nathorst fully realised that the fossil botanist must collect and indeed alternate between field and laboratory.His own contributions to the Yorkshire flora were not numerous, but led to those of his successors in Stockholm, Halle and Florin (both of whom developed his ideas) and above all to those of Hamshaw Thomas of Cambridge who worked for some time with Nathorst and devoted much of his life to the study of this flora.Although I never met Nathorst, I regard my own work as the application of his ideas.GEOLOGY Geological progress in N.E.Yorkshire outstripped botanical work.As early as 1829 Phillips had recognised an ' Upper' and ' Lower' Estuarine Series separated by marine incursions, and soon after he recognised a second incursion, the Millepore Bed, when he distinguished a 'Middle' Estuarine Series.Later still a third marine incursion was recognised, the Ellerbeck Bed, but this led to no change of names of the plant-bearing rocks.In 1892 the Geological Survey of the area was completed (Fox-Strangways) and no considerable alteration has since been made.The memoir of Wilson (1948) differs chiefly in omitting much local detail.Arkell (4933) summarises progress.The plant-bearing rocks have already been described in outline (Harris, 1952(Harris, , 1953) ) and only the briefest summary will be given here.A full account will be given in the second part of this monograph when the description of the plants is complete.Almost all the plants are found in the freshwater rocks which have long been called the ' Estuarine Series ', but as they are purely deltaic the term ' Deltaic Series ' has been substituted and is used here.The following table is based on Hemingway (1949): Marine Oxfordian, many zones.Marine Callovian, macrocephalus zone. Freshwater Upper Deltaic ( = Upper Estuarine).Marine 'Grey' or 'Scarborough' Limestone, blagdeni zone. Freshwater Middle Deltaic Gristhorpe Series ( = Middle Estuarine). Yons Nab Marine Series.Marine Millepore Bed and Whitwell Oolite, possibly discites zone. Freshwater Middle Deltaic Sycarham Series ( = part of Lower Estuarine).BRYOPHYTA 7 Hepaticites arcuatus (L.&H.)HarrisText-fig. 2 a-f 1836 Fucoides arcuatus Lindley & Hutton, p. 93, pi.185.(Poor figure.)1864 Fucoides erectus Leckenby, p. 81, pi.11, fig. 2 a , b. (Good thallus.Referred to in text as figs.3 a and 3 b.Fig. 2