CONCLUSION. 



In the present volume we have practically confined our attention 

 to the fossil plants from the Inferior Oolite (Bathonian) strata of 

 the Yorkshire coast. A comparison of the Yorkshire flora with 

 those of the Stonesfield Slate and other Jurassic horizons will 

 he more appropriately undertaken after the completion of the 

 systematic treatment of the species in a succeeding volume. The 

 flora with which we are now concerned is the richest among 

 Mesozoic floras from British localities hoth as regards the numher 

 of species and the abundance of material, and is scarcely surpassed 

 by any assemblage of fossil plants from extra-British regions. 



A general survey of a geological flora should include the con- 

 sideration of such points as the following: (i.) The geographical 

 distribution of the several types composing the flora; (ii.) a com- 

 parison with older and younger floras, and with recent species ; 

 (iii.) the conditions under which the plants grew ; and (iv.) the 

 recognition of the most characteristic species which may serve as 

 the best indices of geological age. 



In attempting to determine the geographical range of the several 

 elements of the Yorkshire Coast flora, we have to face serious 

 difficulties. It is often impossible to decide whether an English 

 species is identical with or merely closely allied to a species 

 recorded from another region. If we ignore all records but those 

 which can be interpreted with satisfactory accuracy, without any 

 doubt as to the specific position of the plants, our comparisons 

 would be restricted within limits which would not enable us to 

 do full justice to the available data. In the comparison of floras 

 more or less widely separated geographically, the recognition of 

 specific identity is naturally desirable, but the object of a com- 

 parative study of fossil floras is primarily to determine resemblances 

 and differences as regards the general facies of the vegetation rather 

 than the absolute specific identity of individual plants. In the 

 following table I have indicated the geographical range of the 

 English species, without giving any indication as to the degree of 



