6 



NOTES OX CONCRETIONS 



11. In Cape Breton, and at Arisaig, N. S., there are bands of 

 limestone composed entirely of concretions no larger than 

 mustard seeds, and sometimes much smaller. They represent 

 our oolitic rocks. Those of Cape Breton belong to the carbon- 

 iferous formation, and those of Arisaig are associated with the 

 lower carboniferous conglomerates and sandstones of the coast 

 rocks. In my notes of 1873 of a portion of the Arisaig rocks, I 

 wrote : " At Grant and McDonald's Cove the sandstones are in 

 contact with a band of light gray limestone (Photo. No. 18), 

 resting on six feet of bluish gray calcareous shale, holding a 

 Lingula and two small bivalves resembling Modiolopsis, but 

 not determinable with certainty. In the limestones of which 

 there is a thickness of about twenty feet, I found two species of 

 Hhynchonella and one Athyrix. A great part of this limestone 

 is oolitic, or made up of minute concretions." Fig. 3 is a micro- 

 drawing from a thin slice of the Cape Breton limestone magnified 

 about twenty times. 



FIG. 3. 



