G24 E. M. KIXDLE CAXADIAX PLEISTOCENE C02s CRETIO^'S 



contrast with the occurrence of concretions along the Ottawa Eiver and 

 some other streams abnndantly or sparingly, according to the location , 

 is their absence or scarcity in the same clays where cut by ditches. The 

 general absence of concretions from the clays cut by ditches leads to the 

 inference that their development is limited to a superficial zone of clay 

 which has been exposed for a considerable period in the stream-bank 

 sections of the district. This conclusion, it may be noted, is in harmony 

 with, the view now generally accepted that the silicification of fossils is 

 ordinarily a wholly superficial phenomenon which takes place but a very 

 slight distance below the surface of the limestone in which the fossils 

 are embedded/- Professor Hughes"^^ likewise found the beekites to be 

 sujjerficial in their occurrence, being absent where "the limestone frag- 

 ments were not decomposed.'^ 



Concretions occur abundantly at only a few localities along the streams. 

 Careful search of the clay banks along the Ottawa Eiver above Greens 

 Creek will seldom disclose more than one or two concretions within the 

 limit of a hundred yards. In the same clays immediately below Greens 

 Creek for a distance of half a mile or more many hundreds of concretions 

 may be seen witliin the same distance limits. Xo other locality near 

 ■ Ottawa or elsewhere is known where the abundance of concretions ap- 

 proaches that observed along the half mile of river bank between Greens 

 Creek and Besserers Landing. Since the peculiar distribution of con- 

 cretions at the mouth of Greens Creek appears to give a clue to an im- 

 portant factor in the formation of the concretions of the clay cut by this 

 stream, their distribution at this point will be stated in some detail. 

 Greens Creek has a width of about 50 feet at the mouth and enters the 

 Ottawa Eiver G miles below Ottawa. A careful search of the clay bank 

 on the east side of the creek was made for 200 yards above the mouth 

 without finding a single concretion. Immediately below the junction 

 of the creek and river concretions are abundant and along the river bank 

 near the low-water stage will average probably five to th3 square foot. 



The clay exposed in the bank of the river and the bank of the cre?k is 

 of precisely the same physical character and the same thickness. The 

 mingling of the water of the creek and river may bo one of the factors 

 responsible for the relative abundance of concretions in the river bank 

 below Greens Creek. Since the concretions are wanting or scarce where 

 the clay is exposed to either creek water or river water alone and very 

 abundant where both river and creek water mav lave the bank, it is diffi- 



*= Henry Xettleroth : Kentucky fossil shells. Ken. Geol. Surv.. 1889. p. 120. 

 *^ T. M. McKenney Hughes : Mlneralogical Mag., vol. vlii, no. 40, 1889, p. 266. 



