212 The Ottawa Naturalist. [February 



rocks. The true nature of the more unusual types and those 

 which bear such a marked resemblance to ordinary conglome- 

 rates, is not nearly so evident, and much confusion has arisen in 

 the past from their wrong interpretation. The explanation* 

 however, of the formation of these limestone breccias is rather 

 simple, and every gradation is discernible at one or other of the 

 various localities where these rocks are exposed. Outcrops which 

 have been subjected to only normal dynamic action show impure 

 bands, more or less continuous, composed of the prevailing light 

 greyish often rusty-weathering gneisses representing, hardened 

 and altered interbedded mud or silt-like depositions. These 

 impure gneissic bands are extremely brittle and thus very liable 

 to break up, while on the other hand, with the applica- 

 tion of the same dynamic or stretching force, the limestome is 

 seen to "flow," filling in the most minute spaces and accom- 

 modating itself to every phase of its new position. With a 

 continuation of the same force with more marked intensity, the 

 limestone gradually recrystallizes and may even become quite 

 massive. The first process in the deformation of these bands is 

 the development of transverse joints as the result of the folding 

 and stretching to which the whole series has been subjected. A 

 further application of these processes of deformation, bands 

 originally continuous become more widely separated, the inter- 

 vening spaces being occupied at once by the extremely plastic 

 and accommodating limestone. In exposures which have been 

 very little subjected to dynamic action, the separated fragments 

 are quite angular and are readily traceable as one continuous 

 band, but where extreme modification has taken place the frag- 

 ments have become so rounded and displaced, owing to differen- 

 tial movement and pressure, that the resulting rock-mass presents 

 in great perfection the characters of an ordinary conglomerate 

 containing well rounded fragments with every appearance of 

 having been water-worn. 



The pseudo-conglomerates belonging to the second division 

 (b) of those having a limestone or dolomitic matrix seem to 

 be confined as a rule to the vicinity of irruptive masses, and 



