554 ISLE OF MAN. GEOLOGY. LIMESTONE. 



either in the immediate neighbourhood of the fundamental 

 rock, or in that of the trap veins. They are attended with 

 marked curvatures of the beds, and will be described in 

 examining the general connexions of the different rocks 

 hereafter. 



The beds of limestone are found to alternate with brec- 

 cias of different characters, above noticed ; but these are, 

 generally speaking, either at the bottom or at the top of 

 the limestone mass. 



Besides these breccias, beds of shale, or of clay, more 

 or less approaching to that substance by its induration, 

 are found interposed among the limestone beds. This 

 is far too common an appearance to require any further 

 notice. 



The colour of the stratified limestone varies slightly 

 in different places, but is generally limited to different 

 shades of dark and blueish grey; the darkest, which 

 approaches near to pure black, being the marble of Pool 

 vash formerly described. 



The differences in composition lie also within narrow 

 limits, and consist in the greater or less predominance of 

 argillaceous earth, as well as of silica, in the calcareous 

 rock. 



Magnesia is also occasionally found as an ingredient, 

 but it is unnecessary to dwell on circumstances of so 

 ordinary a nature, as similar limestones are familiar to 

 geologists. 



It is equally superfluous to detail the texture, frac- 

 ture, and general appearances of this rock, which vary 

 from smooth and conchoidal, to granular or earthy, as in 

 other instances of almost daily occurrence. 



The organic remains are abundantly dispersed through 

 almost every part of the calcareous strata, and of the 

 interposed shales; being however much more numerous 

 and entire in some places than in others. Occasionally 

 they are absent altogether, but they are rarely wanting 

 for any considerable space. Their cavities are in almost 



