58 GEORGE GRANT MacCURDY 



have been chipped from the same parent block, was, according to 

 Sellards, found in the south bank 460 feet west of the bridge, but in 

 stratum No. 3 (Fig. 2). That of these two chips of like material 

 and so near each other in respect to horizontal displacement one 

 should have been found in stratum No. 3 and the other in stratum 

 No. 2 is significant. The question arises whether both might not 

 have been originally in stratum No. 3, one having worked its way 

 down into No. 2 by the aid of growing roots or burrowing animals. 

 While Dr. Sellards does not recall having seen any roots reaching 

 into stratum No. 2 where the spall reproduced in Fig. 1 was found, he 

 admits that roots do penetrate this stratum in places, notably a 



Fig. 1 Fig. 2 Fig. 3 



Figs. 1-3. — (1) Flint spall from stratum No. 2, south bank, 460 feet west of the 

 bridge and near human bones; (2) flint spall of identical material from stratum No. 3, 

 south bank, 460 feet west of the bridge, from sif tings; (3) flint spall from stratum No. 2 , 

 south bank, 460 feet west of the bridge, from siftings (}). Nos. 6964, 7072, and 7049. 



little farther west where flint No. 7055 (not herein figured) was 

 found. 



These spalls were never retouched or utilized. Each has what 

 the French call a plan de frappe ("plane of percussion") and a 

 well-marked bulb of percussion. The inner or conchoidal surface 

 is fresh and the edges are unworn. They were evidently chipped 

 from the parent block not far from where they were found. At one 

 time the presence of a bulb of percussion was looked upon as a sure 

 sign of human agency. Certain rare examples from the base of 

 the Eocene at Belle-Assise, Clermont (Oise), and from the Oligocene 

 at Boncelles, Belgium, are proof that the bulb is not an infallible 

 sign. By accidentally letting one flint fall upon another, the writer 

 has on one occasion unintentionally caused the production of a bulb 

 of percussion. It is, however, quite logical to assume that the vast 



