OUTWASH FROM THE OLDEST DRIFT. 249 



detritus of our ancient river. * * * When the Allegheny River ran 300 feet above 

 its present level it overflowed its banks at this ppint, and deposited its detritus in the 

 cemetery and in this valley. Between Neg'ley and Highland avenues is another 

 deposit of a similar character, showing a similar overflow when the Allegheny River 

 was 300 feet higher than at present. This "overflow" deposit consists of 16 feet of 

 gravel above and at least 22 feet of fine sand below; the gi'avel contains much foreign 

 matter, some large pebbles and many angular stones, sometimes a foot in diameter. 

 About 8 feet from the top was found a rectangular stone which measured 33 inches 

 bjf 36, by 13, with sharp edges and angles; it was a conglomerate, distinctly stratified, 

 and composed of vevy small grains of well-rounded white quartz. The nearest bed- 

 rock was found in a ravine 27 feet below the base of the gravel. 



UPPER OHIO VALLEY. 



The terraces on tlie Upper Ohio being a direct continuation of those 

 on the Allegheny, a similar series of deposits is presented. The first promi- 

 nent remnant of the high-level glacial gravel is found in the western part 

 of Allegheny, and extends from that place down the valley past Bellevue, 

 a distance of nearly 5 miles. This was recognized as a glacial terrace by 

 White, in 1876.^ The altitude is shown by a topographic map of Alle- 

 gheny to reach in places 975 feet above tide, and the general level of the 

 surface is above 950 feet. The width averages about a half mile. Several 

 gravel pits have been opened. One on Woodland avenue, described by 

 Jillson, "consists of 3 or 4 feet of clay and loam resting on 15 to 18 feet of 

 gravel, and this on sand which has been excavated more than 15 feet." In 

 the gravel was a granite pebble 5 by 6 inches in diameter, as well as several ' 

 smaller pebbles of Canadian rocks. An exposure noted by the writer near 

 California avenue has the following beds: 



Section of (pxmel jnt on high terrace in Allegheny. 



Feet. 



1. Sandy loam 4-8 



2. Fine gravel, with ranch sand intermixed 3-6 



3. Sand, cross-bedded 4-5 



4. Gravel, like No. 2 6-7 



5. Sandy and gravelly material exposed 5-6 



The gravel extends down to a nearly level shelf of rock, standing 890 

 to 900 feet above tide, or 75 to 85 feet below the highest parts of- the terrace. 

 A depth of 75 to 85 feet apparentl}- holds all along the terrace. Wells in 

 Bellevue 60 feet in depth have not reached the bottom of the gravel. 



A few miles farther down the Ohio, near Sewickley, a narrow terrace, 

 standing about 200 feet above the river, was found by Jillson to carry 



' Second Geol. Survey Pennsylvania, Kept. Q, pp. 12, 175. 



