6 NOTES ON 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 lmestones of which 
there is a thickness of about twenty feet, I found two species of 
Rhynchonella and one Athyris, 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. 
