ISLE OF MAN. GEOLOGV. LIMESTONE. 557 



character can only be discovered after a deep fracture. 

 In these cases it becomes yellow and dark brown; thus 

 assuming, in some instances, the aspect of the yellow 

 magnesian limestone of England. 



Brown spar is occasionally found in the rifts, and also 

 in nests occupying irregular cavities. It must however 

 be remarked that the same mineral exists generally in 

 the rifts also of the stratified limestone, being in both 

 cases crystallized in its most ordinary form; the only 

 difference being, that in the latter case it is white with 

 the usual pearly lustre, while, in the unstratified rock, 

 it is brown, and may often with equal propriety be termed 

 calcareous iron ore. 



In general, no shells or organic remains are to be found 

 in the unstratified rock ; but as some of the exceptions 

 are important, it is necessary to be more particular in 

 tracing them. 



Near the Santon river, at the junction of the schist, and 

 where one of the most conspicuous and interesting of these 

 masses is to be seen, no shells occur for a considerable 

 space. But as the unstratified rock approaches to the strati- 

 fied, it undergoes a gradual alteration, the crystalline texture 

 gradually passing into the earthy, and the change being 

 complete when the beds have put on that which may 

 be called their natural form. The organic remains in- 

 crease in the same proportion, being sparingly found 

 at first and in the intermediate parts of the change, and 

 becoming abundant when that is complete, as they were 

 absent before its commencement. In one place only they 

 were found imbedded in the crystalline limestone, but 

 in this place their forms were less accurately preserved 

 than usual ; a remark which was confirmed in other 

 instances where they were found in a similar situation. 

 It is important to note, that in these instances the organic 

 substances are similar to those found in the stratified lime- 

 stone ; and they prove the original identity of the cal- 



