724 STUDIES FOR STUDENTS 



Thus Robert Bell has described the dolomitic limestones under- 

 lying the waters along Grand Manitou Island, the Indian 

 peninsula and adjacent portions of Lake Huron and the Georgian 

 Bay, as pitted and honeycombed in a very peculiar and striking 

 manner. This corrosion, it is believed is, produced through the 

 solvent action of sulphuric acid in the water, the acid itself aris- 

 ing from the decomposition of the sulphides of iron pyrites and 

 pyrrhotite, which exist in great quantities in the Huronian rocks 



to the northward.' 



George P. Merrill. 



'J3ull. Geol. Soc. of America, Vol. VI, p. 47-304. 

 (To be continued.) 



