( 185 ) 



EXPLANATION OF THE PLATES. 



THE geological map of the eastern part of Yorkshire is intended to convey a correct 

 general idea of the relative situation and extent of the principal mineral masses ; and 

 though the scale to which it is drawn does not allow of minute accuracy, the outlines 

 will be found sufficiently exact. I claim no merit for introducing the unconformed 

 direction of the strata beneath the Wolds, the correct line of the Kimmeridge clay, nor 

 that of the Bath oolite formation, because these points have been long since determined 

 by Mr. Smith, who will, it is hoped, soon publish the results of his long and successful 

 researches, on a splendid geological map of the county. The colours used on the map 

 sometimes include a number of strata, which in the section have different tints assigned 

 them. The diluvial gravel, clay, &c. of Holderness are represented by a bright 

 purple, but it has not been deemed necessary to mark these accumulations in the vales 

 of York, Pickering, and Cleveland. The white chalk is left uncoloured, but the red 

 layers at its base are indicated by an appropriate narrow red line. The greenish 

 blue, adopted from Mr. Smith, represents the great clay formation of the vale of 

 Pickering, &c. of which the upper part corresponds to the gault, and the lower to the 

 Kimmeridge clay. The coralline oolite formation occupies the space of the light oraage, 

 and the Oxford clay and Kelloways rock beneath, range along the line of the dun purple. 

 To have coloured across the moorlands the sub-divisions of the Bath oolite forma- 

 tion, which are visible on the coast, would have been hardly practicable ; and the 

 method of grouping them, as Mr. Greenough has done, has the great advantage of 

 exhibiting at once the general analogy of these rocks and those in the south of England ; 

 whilst their differences may be easily gathered from the detailed sections. The bright 

 yellow includes the cornbrash, upper sandstone and shale, Bath oolite, and lower sand- 

 stone and shale, whilst the inferior oolite, or dogger, is marked by the narrow stripe of 

 full orange. The lias formation is coloured blue, and the new red sandstone, pink ; the 

 same bright purple is employed for the diluvium both in the map and in the sections ; 

 and the other colours in the latter are fully explained by references engraved on the 

 plates, which also contain the necessary scales of altitude. 



REFERENCE TO THE PLATES OF ORGANIC REMAINS. 

 Plate I. Chalk, page 118. Speeton Clay, page 123, 



Fi g- Fig. 



1. Spongia plana. * 4. Spongia Benettiae. 



2 capitata.* 5 marginata. * 



3 osculifera. * 6 convoluta.* 



Bb 



