lOG DESCRIPTION OF THE STRATA. 



The qualities of this rock, however, ai'e far from being uniforni. 

 Sometimes, as at Cloughton wyke, we find a considerable thickness 

 of grey limestone over the blue; in other instances, the grey limestone 

 is found both above and below the blue, and the latter is almost ex- 

 cluded; in others, the blue so far predominates, that the grey is 

 thrust out. Sometimes the one passes into the other, and not unfre- 

 quently we meet with a clouded mixture of both ; as in the blue and 

 grey limestone imder the oolite. The grey is occasionally yellowish, 

 or brownish; but more frequently dusky or ash-coloiu'ed. The blue 

 is in some instances very light, or blueish grey; in others, very dark; 

 and in others, it is more properly black than blue. Some parts of the 

 rock, especially in the grey limestone, are sandy and schistose; 

 others are very compact, and highly calcareous. Sometimes the 

 stone abounds with shells; in other instances, it contains few or none. 

 In some specimens, the recent fracture presents a dull, earthy aspect; 

 in others, we see a mixture of small shining crystals; in others, the 

 crystals are more numerous ; and in a few, the structure is almost 

 wholly crystalline; in which case, and in some of the other instances, 

 the crystals are usually large and oblong. The most crystalline speci- 

 mens are not of the darkest colour, some of them being of a light 

 grey : yet, in general, the stone is most compact, where it is of the 

 deepest blue. 



We have already seen, that at Cloughton wyke, these limestone 

 beds succeed the ironstone, or ferruginous sandstone; and we have 

 now to remark, that although we do not find the ironstone beds at- 

 ttniding the limestone in its progress in the interior, yet we find, in 

 almost every place where the latter occurs, a portion of iron inter- 

 mixed with it. Ferruginous patches and veins are very common; the 

 blocks of stone often appear incrusted with iron ; and the weathered 

 faces of the beds frequently have a rusty aspect, the iron making its 

 iippearance where the stone is partially decomposed. 



