168 Microscopic Structure of Canadian Lime stoves. 



fragments of shells and crinoids, which, like the fragments of some 

 of the modern limestones of Florida, bear evidence of the rolling 

 action of the surf or of strong currents. Another variety is fine 

 and compact like the upper part of the Trenton at Montreal, and 

 shows a homogeneous calcareous and earthy paste filled with frag- 

 ments of shells, crinoids, and corals. Figs. 4 and 5 represent the 



Vil 





igp 



», 



«W «T " - 





^!iS 



Fig. 4. 



Fig. 5. 

 Figs. 4 & 5. — Limestone from Pt. Claire Quarries, (10 diams.) 



two last varieties, and may be taken as fair specimens of the ma- 

 terial of the piers of the great railway bridge, which solid and 

 durable though they are, are composed of shelly fragments, that once 

 drifted like snow before the ocean currents. The Chazy lime- 

 stone of Isle Jesus is characterised by Sir W. E. Logan, as " a 

 cemented aggregation of organic remains." I have not examined 

 this stone, but that of the same formation in the vicinity of Mon- 

 treal, consists almost entirely of broken brachiopodous shells, many 

 of them probably the Atrypa plena, which is so abundant in these 

 same beds. (Fig. 6.) 



To persons unfamiliar with such subjects, it is a striking fact 

 that the buildings of our cities are constructed of the debris of the 

 skeletons of marine animals, belonging to a bygone period of the 

 earth's history, and that these same remains constitute sheets of 

 limestone extending over many thousands of square miles, with a 

 thickness of several hundred feet. As already stated, however, these 



