68 The Ohio Naturalist. [Vol. IV, No. 3, 



the bone bed or top of the formation. As the quarry is at about 

 the top of the hill it is probable that this bed has been carried 

 awa}' for some feet back from the brow of the bluff into the field. 

 It might be wished that this laj'er were present to give a more 

 certain determination, but as the interval between the smooth 

 la3'er and the bone bed is fairh' constant the presence of the lat- 

 ter is not so important as would appear at first. 



The sections of the hill and well are given in the tables. It 

 will be seen that the total thickness of the Columbus exposed is 

 109 feet. Assuming an interval between the bone bed and smooth 

 bed of 9 feet (an inch or two less than that shown in the quarries 

 a mile and a half below the dam site), we would have a thickness 

 for the formation of no feet, thus checking to within 2 feet of 

 the determination from the State House 3'ard well. 



Section of Bank. Feet. In. 



Total 

 P'eet. Iti. 



To bone bed (not exposed) ? i 2 126 



Top of quarry, no sign of bone bed 125 



Upper Columbus exposed in quarry 8 



Smooth layer 117 



Quarry extends a few inches below smooth layer 



Mostly covered, occasional ledges exposed to river level 64 . . 53 

 Section of Well. 



Gravel and soil 2 55 



River level 53 



Gravel and soil to lop of rock 2 7 53 



Heavy bedded some layers come out more than 2 feet 



thick 24 S 50 5 



Thin bedded much waste in core 7 2 25 9 



Heavy porous breccia, base of Columbus 2 4 iS 7 



Hard course with dark bands top of Monroe <S 16 3 



Mostly thin bedded, dark . . 3 10 15 7 



Purer limestone 9 11 9 



Dark thin bedded resisting acid i .. 11 



White, purer stone 9 10 



Heavy bedded i 9 9 3 



Dark, very hard resisting acid 6 7 6 



Hard, heavy, dark stone with little waste 7 . . 7 



The determination is subject to the following sources of error : 

 I , waste in the core of the well which would have the effect of 

 making the l)ase of the Columlnis too high with a maximum 

 value of 2 inches ; 2, a variation in the level of the water between 

 the time of boring the well and that of measuring the hill amoun- 

 ing to possibly 6 inches in the other direction : 3, errors in level- 

 ing amounting to possibly 3 feet either way : the city contour 

 maps check the leveling and preclude the possibility of greater 

 error, /. r., the top of the quarrj' lies between two contour lines 

 having a five foot interval ; 4, variation in the interval between 

 the smo(jth bed and bone Ijed with a probable maximum of 8 

 inches. 



Fargo, N. D. 



