GEOLOGICAL PAPERS III 



that superficial obsenation gives the impression that the deposit 

 extends to the bottom of the gully, as shown by Fig. 2. 



With reference to the origin of the calcium carbonate (CaCOs) 

 it may be said that most calcareous deposits made by springs occur 

 in limestone regions, but no limestone is known to exist in the 

 vicinity of this deposit. Mine shafts to the north and the bluffs 

 across the river to the south expose only a silicious shale. How- 

 ever, along the lower rim of the spring basin on either side of the 

 outlet remnants of a glacial conglomerate are exposed, and one 

 of these exposures is along the rail fence at Mr. Eaton's right in 

 Fig. I. This conglomerate is firmly cemented with calcium car- 

 bonate (CaCOj). If the basin of the spring were at one time 

 filled by a glacial conglomerate of which the present exposures 

 are small remnants, an adequate source for the calcareous deposit 

 would be furnished. Were the glacial conglomerate at one time 

 much more extensive than now% the reduction to the present lim- 

 ited remnants would accoimt for a decrease in calcium carbonate 

 (CaCOg) supplied to the spring, and hence explain the cessation 

 of deposition of that substance from solution. 



Xo ver}' definite evidence of the age of the tufa was noted. 

 The conglomerate, because of its highly indurated condition, 

 doubtless belongs to a stage of glaciation as early as the Illinoisan. 

 While the unindurated gravels beneath the tufa are similar to 

 those overlying the conglomerate, and both of these gravel depos- 

 its probably are of AMsconsin age.' These considerations favor 

 the idea that the tufa has been deposited since the Wisconsin 

 Stage of Glaciation. 



OX THE EARTHQUAKE OF JAXUARY 2. 1912, IX THE 

 UPPER MISSISSIPPI VALLEY. 



AxTOx D. L'dden, 



Augustana College, Rock Island, Illinois. 



On Januar>' 2, 1912, the northwestern part of Illinois and sur- 

 rounding territory' were visited by an earthquake. Immediately 

 after the shock the author began to collect information concerning 

 the effects of the disturbance. The description in this paper is 

 based upon the accounts of the earthquake contained in sevent)-- 



' Danville Folio, p. i, et seq. 



