ISLE OF MAN. GEOLOGY. LIMESTONE. 56l 



stances, their mode of weathering-is altered, from the 

 former flaky and even, to the irregular cavernous and 

 pyramidal manner by which the unstratified rock is dis- 

 tinguished. Their composition and general characters 

 undergo corresponding changes. As already remarked, 

 the organic substances gradually disappear, and the 

 earthy aspect gradually also becomes converted into 

 the crystalline, so that the stratified and the unstratified 

 rocks cease at length to possess any mineralogical dis- 

 tinction. 



It is further necessary to observe, that these changes 

 occur in two distinct modes. The first may be traced 

 by following the progress of each individual stratum from 

 a point near the schist to one at a distance from it, and 

 is seen in those cases where the edges of the strata come 

 into contact with the fundamental rock.* The next occurs 

 where the unstratified rock lies between the schist and 

 the stratified one, and takes place, according to the order 

 of succession in the strata, in the following manner.f By 

 degrees the irregular appearance of the unstratified mass 

 diminishes, and it is then succeeded by an irregular bed 

 having a rude conformity to those of more regular form 

 which are to follow. The succeeding strata become gra- 

 dually more even, and more resembling the ordinary strati- 

 fied and prevailing limestone, till a perfect uniformity at 

 length takes place. A complete transition may therefore 

 be traced, in this direction also, from the unstratified to 

 the stratified rock ; and that transition is accompanied 

 by the same circumstances with regard to the mode of 

 weathering, the appearance and number of the organic 

 remains, and the texture, as have just been pointed out in 

 the other case. 



This account of the junctions, and of the transitions 

 of the two limestones, must not however be concluded 

 without mentioning, that other marks of change, and indi- 



* Plate XXVII. fig. 1. f Plate XXVII. fig. 2. 



VOL. II. O O 



