Jan., 1904.] Thickness of the Columbus Limestone. 67 



previously be allowed to dry at least twelve hours. Furthermore, 

 the dish should be heated slightly above the melting point of the 

 beeswax before the wax is poured in, and then allowed to gradu- 

 ally cool before an open-front gas stove, thus allowing the bottom 

 layers of the wax to harden first. This prevents the separation of 

 the wax from the side of the dish as well as the formation of 

 cracks on the surface. Trays such as described have been in use 

 in the laboratory at Kenyon College for more than a year, and 

 have been found practical in every respect. 

 Kenyon College. 



THE THICKNESS OF THE COLUMBUS LIMESTONE. 



Robert F. Griggs. 



So far as is known there is no exposure of the total thickness 

 of the Columbus limestone. On account of its lithological simil- 

 arity to the Monroe limestone below, the two are not usually 

 separated in well records so that exact determinations from this 

 source have been hard to get.* In the fall of 1900, however, the 

 city of Columbus, in connection with a proposed storage dam in 

 the Scioto River, drilled several wells into the rock to test its 

 ability to withstand hydraulic pressure. Most of these were at 

 such high levels on the bank that they did not penetrate to the 

 Monroe. Two, however, Nos. 9 and 10, were drilled from 

 near the surface of the river and passed several feet below^ the 

 base of the Columbus. No. jo was located on the west bank, 

 which is steep at that point. It was thought that by taking the 

 section of this well and that of the bank the whole thickness of 

 the Columbus could be obtained. The well was not driven in the 

 ordinar}' manner, where the rock is broken into bits by a heavy 

 drill and so mixed that the precise determination of any level is 

 impossible, but a solid core was taken out, which broke only at 

 the bedding planes and weak places. This core, together witli a 

 very complete record, are preserved in the City Engineer's office. 

 It allows the determination of the line between the two forma- 

 tions to a fraction of an inch and the measurements throughout 

 are much more accurate in the boring than those of the bank, 

 which were taken with a Locke level, and so not susceptible of 

 great accurac}'. 



The rock in the bank above is mostly covered, but fortunately 

 a small quarr}^ has been opened at the top of the hill which shows 

 the top of the smooth la5-er. The quarrj' does not extend up to 



-The well in the State House yard at Columbus, as iuterpreted by Newberry, shows a 

 thickness of 13S feet for the Coruiferous. which includes both Columbus and Sandusky 

 formations. The upper component is shown to have a thickness of about 30 feet by 

 numerous exposures in Franklin and Delaware Counties. Deducting this leaves a thick- 

 ness of loS feet for the Columbus. Unfortunately, however, the record of this well ha.s 

 been found to be unreliable in some particulars and so is of .scant authority in this case. 



