SURFACE GEOLOGY. 443 



coal and of the sandrock of the Coal Measures, all evidently of home 

 origin. The pebbles of coal could not have traveled far — the material 

 is too soft to endure the friction and rough usage of a long journey. 



The Drift terraces are found along the Ohio, Muskingum, Licking, 

 Hocking, and Scioto rivers, but on no others in the Second District. 

 These are the only streams whose sources lie within the area of the general 

 Drift, and, consequently, the only ones which could obtain the materials 

 needed for true Drift terraces. These terraces have been more or less 

 wasted and reduced in height since they were formed, but eighty feet 

 above the stream is about the elevation of those best preserved. Being 

 dry and easily drained, they afford desirable locations for the towns and 

 villages of the present inhabitants, as they did for the Mound-builders, 

 whose finest works are generally upon them. Zanesville, Marietta, Lan- 

 caster, Gallipolis, Iron ton, Portsmouth, and other towns of less size, are 

 built wholly or in part on Drift terraces. The Ironton terrace has more 

 clay mixed with the sand than is usual. The terrace on which a part of 

 the city of Lancaster is built, the new and beautiful court-house having 

 a commanding site on the summit, is one of the old Drift gravel banks. 

 It is from seventy- five to eighty feet above the present bed of the Hocking 

 River. We have now only a remnant of the original terraee, for the 

 waters have swept around in rear of it, and left only an insular hill in 

 the broad fertile valley. On the southern edge of the present hill the 

 gravel is very coarse. This gravel at some points is found to be cemented 

 together by carbonate of lime, and a stratum of coarse pudding-stone has 

 been formed, which is used for rock-work, ferneries, ice-houses, etc., 

 where picturesque effects are desired. A similar pudding-stone is found 

 in a Drift terrace a few miles below Logan. 



Marietta is built on a large and beautiful terrace, formed at the conflu- 

 ence of the Muskingum and Ohio rivers. It is composed of sand and 

 gravel, the sand in some places fine enough for molders' use. The gravel 

 is often quite coarse, and contains pebbles of considerable size. In the 

 south-eastern portion of the terrace, where it is crossed by Putnam street, 

 there is a well-defined horizontal layer of fine blue clay, which indicates 

 that at one time the currents of the two streams were of such equal level 

 and equal force as to form an eddy of still water, from which the fine 

 clay sediment was deposited. 



The terraces at Columbus and vicinity are broader than the usual val- 

 ley terraces, and constitute a part of a far wider outspread of Drift mate- 

 rials in the more fiat country to the north The transition from the val- 

 ley Drift to the general northern Drift, as it has been distributed and 

 arranged by water, is almost imperceptible. Perhaps the same aqueous 



