454 



CANNA. GEOLOGY. 



add that the compressed forms of lignite, brown coal, 

 and surturbrand, so changed into bitumen, display pre- 

 cisely the appearance of the wood found in the trap 

 conglomerates. 



Referring to the circumstances just mentioned, there 

 is reason for presuming that these conglomerates have 

 all been generated by the deposition of abraded matters 

 from water. It is difficult, perhaps impossible, to 

 conceive that the pebbles of any of the three orders 

 of conglomerates could have existed while in contact 

 with a fused mass of rock; or that a union more 

 intimate should not have taken place between the pebble 

 and the bed at the planes of contact. It is still more 

 difficult to believe that sand so minute and of so fusible 

 a nature, should be agglutinated by the action of heat 

 without being at the same time fused. It is clear that 

 they cannot all have been formed under the circumstances 

 from which the untransported breccias have resulted, 

 since the rolled masses found in some of them bear the 

 evident marks of motion. It is possible however, that 

 those which contain only angular fragments, again 

 cemented by the same substance, may have been thus 

 formed. Their analogy with the corresponding class 

 of breccias is very strong, and there is perhaps no 

 great difficulty in admitting that if limestone, or quartz, 

 or schist, comminuted to the state of mud, is capable 

 during long repose and under the influence of other 

 causes as yet concealed, of forming a solid mass of 

 rock, some of the modifications of trap which exhibit 

 the least of a crystalline texture, may also be formed 

 in similar circumstances. The same cause will equally 

 account for the consolidation of the first variety, and we 

 shall thus be in possession of a resource for explaining, not 

 only this particular circumstance, but some other pheno- 

 mena that have been supposed to interfere with that 

 theory which attributes the general origin of the rocks 

 of the trap family to igneous fusion. The more perfect 

 stratified appearances which these rocks sometimes put 



