14 LOWER PENINSULA. 



feet of sand layers with discordant stratification; the layers are 

 bent into tortuous, serpentine flexures. Incumbent on these sand 

 beds is a thick coating of apparently non-stratified boulder drift, 

 differing from the lower boulder drift by less clayey, more sandy 

 constituents, and by having its boulders much less distinctly drift- 

 marked. In the surface of the sand deposits, underlying these 

 upper boulder drift masses, narrow, acute ravines are observed, 

 which are filled with boulder drift. Sections through them are 

 laid open by the railroad cut. It seems as if the surface of the 

 sand deposits had been exposed for a while to the atmosphere, 

 and deep, narrow ravines cut into them by rain-streams, which sub- 

 sequently were filled out with the boulder drift, without disturb- 

 ing the sharpness of their angular contours. How this was effect- 

 ed I am not prepared to explain. The flexions of the sand strata, 

 I suppose, are caused by lateral pressure exerted by sliding of the 

 masses. I have frequently observed similarly bent sand deposits 

 in other localities — as, for instance, in the bluffs of Manitou Island. 



The incoherent masses of gravel and of sand become in certain 

 localities firmly cemented into conglomerates and sandstones 

 by carbonate of lime, deposited by springs percolating the gravel 

 and sand banks. Such conglomerates, forming large,. bulky masses, 

 of concretionary form, are abundantly seen in the above-described 

 bluffs on the shore of Lake Michigan, and more southward, at the 

 mouth of Muskegon and of Kalamazoo rivers ; also in the gravel 

 pits along the railroad from South Haven to Kalamazoo, and in a 

 great number of other places. Near the mouth of Kalamazoo 

 River, at Richmond, I have seen such sand rock of the drift in 

 very compact, hard ledges, which would make a durable building 

 stone. Sometimes we find, instead of lime, the sand or pebbles 

 cemented by hydrated sesquioxide of iron, but not in so large 

 masses, and always close under the surface, while the calcareous 

 conglomerates are often found interstratified with other drift beds 

 quite remote from the surface. These ferruginous conglomerates 

 have the same origin as bog-iron ores, from springs holding iron 

 in solution by means of carbonic acid, and depositing it, in some 

 cases, as incrustation over pebbles and sand, and in others, over vege- 

 table stems, which subsequently decay and leave the ore in the 

 porous condition in which usually it is found. 



Bog iron occurs very frequently in small patches of marsh land 



