LIMESTONE Sf CALCAREOUS SANDSTONE. 75 



are usually so abundant, that when the mai'l is dislodged from tlie 

 cavities in the stone, the latter presents a singularly cavernous ap- 

 pearance, like the scorifs from a volcano, or the slag from a furnace, 

 though on a far larger scale. At Rowlston scar, in particular, where 

 the winds and rains carry off the marl as soon^as it is exposed, the 

 face of the bed appears as if excavated into small grottos, caverns, 

 openings, and sinuosities of all descriptions ; while the solid parts of 

 the rock are left projecting in an equal variety of forms, sometimes 

 in sharp points or knobs, sometimes in crooked ridges or lines, re- 

 sembling the roots or stalks of some shrubs. The rock itself varies 

 in quality, being in some parts very hard, in others softer ; in some 

 so calcareous as to deserve to be called limestone, in others a true 

 sandstone. The variety is increased in some places by a mixture of 

 ironstone ; and the oxide of iron serves, in many instances, to deepen 

 the colour of the marl. 



In several parts of these beds, the marl seems to have resulted 

 from the decomposition of limestone nodules ; for such nodules, or 

 nuclei, are often found imbedded in the rock; instances of which 

 occur at Rowlston scar. In other places, however, as at Nawton, 

 and near Whitwell, it is far too abundant to be attributed to such a 

 cause. Indeed, the yellow marl, in some of the spots alluded to, 

 seems almost to form an independent bed, the proportion of sandstone 

 intermixed with it being very small. Thin beds or seams of this sandy 

 marl do actually exist in an independent state, between some of the 

 strata in Rowlston scar; but they are much lower than the cavern- 

 ous bed now described. 



In that part of the Filey rocks which corresponds with this bed, 

 the marl is found in smaller quantity; partly in thin seams or sinuosi- 

 ties, partly disseminated through the stone in small crevices, and 

 giving it a yellow tinge when recently broken. The rock also, as at 

 Rowlston scar, is of very different degrees of hardness ; and hence,, 



