MODIFIED BAR HYPOTHESIS 237 



fresh waters would probably flow over the top of the highly charged 

 waters if the receiving basins were very small, but they would probably 

 mix thoroughly Avith the saliue waters in large basins, and the waters 

 furuislied to the secondary basins would be of the nature postulated. 



in discussions of the bar theory of Ochsenius the backflow from the 

 isolated basin has often been emphasized, but the backflow would be im- 

 portant only where evaporation did not keep pace with inflow. Accord- 

 ing to the postulates of this paper, evaporation kept pace with inflow and 

 the depth of water on the bar was too shallow to allow backflow. 



Jf connected with the open sea, across a bar, animals would come in 

 with the inflowing water, and, perishing on account of the salinity of tlie 

 waters in the. basin of deposition, would make the deposits abundantly 

 fossiliferous; but with the. high concentration postulated under the liy- 

 pothesis outlined above life would have ceased to exist in the supplying 

 basins before the gypsum deposits began and no fossils would he present. 



With the conditions postulated, gypsum deposition might automatically 

 stop. The filling up of the outer basin with sediments would cause more 

 water to flow over to the inner basin, and this fresher water might en- 

 tii'cly stop the gypsum deposition by causing the inner basin to overflow 

 and would prevent any salt being deposited. 



Origin of thick Salt Deposits 



The conditions outlined above are much more favoj-able for thiclv salt 

 deposits than for gypsum. Suppose a sea with a doptli of 1.500 feet 

 were ten times as concentrated as sea-water and had losi most of its 

 gypsum as explained above. 



The water left above the g}'psum wouUl contain about l-") IVet of salt 

 per 100 feet, and if this were evaporated to alxmt oiic-roiii-ili its vtduiiu". 

 or .023 the original volume of normal sea-water, alioiit ! '?'•_. Icot ol' salt 

 wiMild be deposited for every 100 feet of water. (»r n totnl of 1 1.") feet for 

 l..")(Mi foot. A\'ith tliis would be associale(l alioiil •.'!._, per cent of iiii- 

 purities, roiisisting ol CaSO.,, MgSo.,, MgCl.., and Nalir. With A iVcl 

 excess evaporation per year, tlio deposit of 175 feet of salt would be 

 foi-iiitMl in 75 years. 



But many times there are no thick deposits of gypsum below the salt 

 and this is easily accounted for. Suppose that the basin is caused to 

 overllow l)y iiifiow of fresh water and its waters flow into another depres- 

 sion of oni'-ti'Mlh its area, in which no deposits bad prcviouslv been 

 formed. If r\ apoiat mn here keeps pace with inflow after tiie basin is 

 pai'tially filltMl, and if excess eva])oration is 5 feet per year, 820 foet of 



