26 THE JOURNAL OF GEOLOGY. 



river at high water and undermined, and the face breaks down 

 vertically, leaving an exposure as illustrated in Fig. 4. In a very 

 short time the upper portions become loosened and fall below, 

 giving a steep slope as seen in Fig. 5. The process goes on 

 with gradually decreasing rapidity, and if the river does not 

 again encroach seriously, a practically stable slope is reached, 

 as shown in Fig. 6. Such a talus may be hundreds or even 

 thousands of years old, but there is rarely any means of deter- 

 mining its exact age. If the gravels are homogeneous in char- 

 acter, the talus will simulate their normal condition so completely 

 that the distinction cannot be made out in ordinary gullies or by 

 unsystematic digging. If the gravels contain varied strata the 

 talus will be composite, and will be more readily distinguished 

 from at least portions of the material in place. 



Now it is important to observe what may be the possible art 

 contents of such a talus as that shown in Fig. 6. It may con- 

 tain all objects of art originally included in that portion of the 

 gravels represented by a, b, c, together with all articles that hap- 

 pened to be upon the surface b, c, beside such objects as may 

 have accumulated from dwelling or shop work upon its own 

 surface, after the slope became sufificiently reduced to be occu- 

 pied for these purposes. A talus is therefore liable to contain, 

 and in the utmost confusion, relics of all periods of occupation, 

 supposing always that there were such periods, from the begin- 

 ning of the formation of the gravel deposits down to the present 

 moment. As a rule such a talus, if art-containing, will have a 

 large percentage of shop and quarry-shop refuse, for the reason 

 that the exposed gravels, and the banks and beds of rivers cut- 

 ting them, furnish, as a rule, a good deal of the raw material 

 utilized by workers in stone, and the shops in which the work 

 was done are usually located upon the slopes and outer margins 

 of the terraces. Although there is the possibility of very con- 

 siderable age for these talus deposits, it is unlikely that any 

 of them date back as far as the close of the glacial epoch or at 

 all near it, for rivers change back and forth constantly, under- 

 mining first one bank and then the other, so that a very large 



