Proceedings of the British Association. 369 



where better shown than along the twelve miles of mural coast 

 locally known as the pictured rock ; the force of the waves im- 

 pelled by the equinoctial gales has fretted and riddled these rocks 

 into the most singular architectural forms ; colossal caverns, into 

 which large boats can enter, are formed under the impending 

 rock. Along this coast of winding bays and headlands, extend- 

 ing altogether four hundred and fifty miles, the action of heavy 

 currents has broken and comminuted the sandstone and gray- 

 wacke, piling up the sand thus formed into elevated ridges, or 

 spreading it out over wide plains. The most extensive field of 

 action occurs between the eastward termination of the primary 

 rocks, near Granite Point, and their reappearance in the elevated 

 mountainous range of Gros Cape, at the head of St. Mary's 

 Straits. Vast hills, or dunes of sand three hundred feet high, 

 are formed along this line, and present a very remarkable appear- 

 ance, from their perfect aridity, their elevation above the lake, 

 and the generally uniform level of their summits. They appear 

 to rest upon more compact beds of clay and gravel, and to have 

 evidently been washed up by the waves and driven landward by 

 the wind. Tempests of sand are thus formed, which spread in- 

 land, burying the tallest trees and carrying desolation in their 

 track. The same wind and wave action is described by the au- 

 thor as taking place on some parts of the coasts of Lakes Huron 

 and Michigan ; dunes are first formed, and then spread inland, 

 bearing sterility over thousands of acres formerly fertile and well 

 wooded. Another effect produced by this drifted sand, is to 

 occasion the formation of pools and morasses along its shifting 

 boundary line, thus injuring other large tracts of country. The 

 recent date of this formation, is often shown by buried trees and 

 fresh-water shells found at great depths in excavating, or exposed 

 by irruptions of the waves. Mr. S. describes other arenaceous 

 deposits forming broad sandy belts, bordering the lakes, and sup- 

 porting a light growth of pine, poplar, and birch ; these he con- 

 siders due to a similar action at an earlier period, when the water 

 of the lakes stood at a higher level and occupied a wider area, a 

 condition which is further indicated by the occurrence of wide 

 lacustrine deposits in the same neighborhood. On the shores of 

 the lakes there sometimes occurs a deposit of iron sand, often a 

 foot in thickness, formed from the magnetic oxide of iron, which 



Vol. xut, No. 2.— Jan .-March, 1843. 47 



