50 STONE IMPLEMENTS [f.th.anx.15 



the bowlders bepaino a comparatively easy matter. They were easily 

 looseneil and fell into the hand of the workuiiin from the matrix of com- 

 ])acted sMiid, as dean and fresh in color as when deposited by the sea in 

 i\Iesozoic times. By thus working on the gneiss surface, antler picks 

 or wooden stakes sharpened by fire would serve to perform the work 

 of undermining and knocking down, whereas our men found it a dilli- 

 cult task to penetrate the closely compacted conglomerate from its 

 upper surface or from the front, even with the aid of steel picks. 



THE .SIXTH TRENCH 



The examination of the third trench made it clear that in certain cases 

 the ancient pits had been tilled, or partially filled, by the sliding of sand 

 and gravel from the quarry wall and from the bluff above. This, fact 

 led to the opinion that some of the unicjue features of conformation 

 observed about the outer point of the terrace were, in a measure at 

 least, due to slides brought about by quarrying ojierations. To one 

 familiar with the ancient quarrying in this locality, the concavity on 

 the horizon of tlie bowlder outcrop and the convexity of profile just 

 below, as seen in the sections, would at once be attributed to human 

 agency. In this case, however, the deformation is on such a scale that 

 natural agencies could alone have accomplished the result. 



On the southwestern angle of the spur, and at a level about 0(» feet 

 below the crest, there is a roundish hump or shoulder 100 teet or more 

 across and rising perhaps 15 feet above what would seem to be a normal 

 jiroflle. This occurs just beneath the level of the bowlder outcrop, and 

 thus has the appearance of a great dump heap to the quarries. 



The character of the rocks forming the bluff is such that they dis- 

 integrate very gradually, and with ordinary activity of the erosive 

 forces a slope of sufficient declivity to invite landslides would not 

 occur. The (piestion arose as to whether extensive quarrying on the 

 face of the bowlder bed and the consequent undermining of the super- 

 posed beds of gravels and sands, here some 40 feet in thickness, might 

 have brought about the sliding of a mass from above sufficient to produce 

 the hump observed. The only jiossible means of arriving at a satisfac- 

 tory solution of the question was by trenching. A series of excava- 

 tions was made covering the profile of the spur from near the summit 

 to the outer base of the convexity that gave rise to the inquiry. The 

 section shown in figure 9 serves to indicate the position of these pits as 

 well as the nature of the i)rofile. The light ])ortions represent the 

 excavations made, and the dotted line at the top indicates the position 

 of the mass supposed to have descended to form the hump. The 

 results of the pitting may briefly be given: The pit at « was in shop 

 refuse similar to that usually found in the quarry dumps higher up. 

 The pit b was carried 13 feet deep through a mass of sand and gravel 

 more or less disturbed, but apparently not by human agency. The 

 material corresponded closely to that of the beds above the quarry 

 level. Near the base, at 12 feet deep, numerous quartzite chips and 



