ISLE OF MAN.' GEOLOGY. BRECCIA. 56*9 



is perhaps easily explained by examining existing alluvia, 

 which are found commencing by a thin edge, and gra- 

 dually increasing in depth as circumstances favour their 

 accumulation. If it be supposed that calcareous matter 

 was deposited on such a compound surface, capable of 

 forming a solid rock, it is evident that at a point above 

 the alluvia it would be immediately united to the fixed and 

 original rock, while these would be converted by its infil- 

 tration in some places, into a breccia of the present struc- 

 ture ; the remainder forming, by the unknown processes of 

 induration, a bed of ordinary conglomerate. Thus the 

 wedge-like form and partial extent of similar rocks are 

 also explained. 



The last breccia which I observed as inferior in posi- 

 tion to the limestone, is remarkable for its structure. It is 

 visible near the Abbey at Balla salla, where its position 

 however can only be conjectured. At Port la Marie, 

 it is actually visible beneath the limestone. It consists of 

 rounded grains and pebbles of white quartz cemented by 

 limestone, and undergoes a slight alternation with, and 

 gradation into that rock, before it finally disappears. It 

 is of inconsiderable thickness, and its analogy to those 

 already described, in origin and nature, need not be more 

 particularly pointed out. 



Such are the varieties of conglomerated rock inferior in 

 position to the limestone. It is possible that there may 

 be others still unnoticed, but there will be no difficulty in 

 classing them, if attention is paid to their structure. When 

 they consist of fragments of the fundamental rock, whether 

 rounded or angular, cemented by a calcareous base, or 

 indurated without that cement, it is probable that they are 

 all inferior to the limestone ; and whenever they contain 

 fragments of the limestone itself, it is equally probable 

 that they have been formed by subsequent changes, after 

 a certain portion or the whole of the calcareous beds had 

 been deposited. In the latter of these cases, they will be 



