PREHISTOIUG ART. 361 



three in number, tlie first being higher, deeper, and more distant from 

 the river than tbe others. These are now marks of the successive 

 stages in the formation of the river valleys. 



The gravelly deposit of the Eiver Marue at Ohelles forms the plain of 

 the river valley. It is from 22 to 20 feet in thickness (Plate 2). The 

 sand and gravel rests upon the original chalk and is about on a level 

 with the' highest floods of the river in modern times. These deposits 

 are of different degrees of fineness and are laid in strata or layers, 

 showing that they were made by the action of the water (fig. 1). The 

 strata are not always continuous, and they differ in thickness and posi- 

 tion, showing the water to have had varying currents. Large, erratic 

 bowlders are found occasionally. The sand and gravel are sometimes 

 intercalated with other strata, which show a change in the surrounding 

 conditions. The most frequent of these is an irregular stratum of calca- 

 leous cement. In other places are pockets or strata containing various 

 solutions of iron, the percolating water from which gives the color to the 

 implements described, and sometimes forms the cement itself. 



There has been much discussion over the time and manner of the 

 formation of these river valleys and the deposit of their sand and 

 gravel as bearing on their antiquity. Such a discussion is unneces- 

 sary here, but all disputants are agreed that implements of human 

 industry are found in these river gravels in positions which indicate 

 tlieir deposit at the time of the original formation and at a distance 

 from the river and depth below the surface which indicate their 

 antiquity to be equal with the earliest dei^osits. Whether they were 

 swept down from the springs which formed the head waters of the 

 river, were dropped on the borders of the stream in the near neighbor- 

 hood, or precisely in what manner they became involved with the sand 

 and gravel in which they are now found, is not only unknown but there 

 has not yet been any entirely satisfactory theory developed. 



A series of these implements is presented, side and edge views, so 

 that the student may understand the differences between these and 

 the thinner leaf-shaped implements and spearheads of other periods 

 and epochs, with which they are not to be confounded. These differ- 

 ences are vital, and as they can not be brought out by a side view 

 alone, an edge view is deemed sometimes indispensable. Some of the 

 implements from Chelles are extremely crude and rough and belong to 

 a very primitive industry, yet they may not be omitted from a work on 

 Prehistoric art. 



The Chelh'en implements figured represent the standards for this 

 epoch. They are mostly oval, with a cutting edge at the point, con- 

 trary to those of the Neolithic period. The body of the implement is 

 thick, after the shape of an almond or peach stone, and not thin aud 

 flat, as a laurel leaf, like those of a later epoch. They were of flint 

 where that stone was obtainable; where it was not, quartz and quartz- 

 ite seem to have been emj)loyed. The flint always broke under a blow 



