DESCRIPTION OF THE DEPOSITS 149 



mile above the confluence of White creek with Los Gatos creek. It is 

 present most abundantly through the middle portion of this stretch, 

 where it forms a pavement over the stream bed as much as 100 feet wide 

 and terrace deposits on the sides of the valley in places as high as 40 feet 

 above the stream. The ledge forming the terrace capping or stream bed 

 pavement is in places 15 or more feet thick. (See figure 2, plate 9.) The 

 width of the pavement, on the valley floor was several hundred feet at 

 the time the stream deposited the conglomerate that now forms the ter- 

 race lining the sides of the valley. The Cretaceous sandstone which 

 underlies the capping is of less induration than the conglomerate and 

 gives way more readily to weathering and erosion, i^s a result, the cap- 

 ping is undercut and large blocks of it break off: as shown in figure 2, 

 plate 9. Thus erosion removes the deposit more rapidly than would be 

 natural in a formation of such hardness were it laid on a more resistant 

 foundation. 



The stream wears a smooth channel in its pavement, cutting directly 

 through the boulders of the conglomerate as if it were a homogeneous 

 rock and producing a polished section. In many cases a fluting of the 

 rock has been caused by the division of the stream into several different 

 channels. The inclusions in the rock are of all sizes and in all stages of 

 decomposition, although the majority are hard and fresh. They include 

 chiefly sandstone of various kinds, serpentine, syenite, chert, quartz, and 

 shale. Among these the most prominent place is assumed by large con- 

 cretions, often several feet in diameter, of extremely hard sandstone that 

 are derived from the adjacent Cretaceous strata. 



The cementing material is yellowish white in color. Although not 

 very hard, it is firm and is present in large amount, forming a complete 

 coating over most of the pebbles, sometimes completely filling the inter- 

 spaces and sometimes leaving the rock porous. The rock varies in com- 

 pactness and hardness, the cement in some places being less abundant 

 and the inclusions roughly agglomerated. The rock gives way more 

 readily to weathering than to stream wear, and where washed by the 

 water it is usually of extreme hardness. It is frequently difficult to dis- 

 tinguish the Quaternary conglomerate from the rocks of the older forma- 

 tions, and the former is apt to lead to confusion for the additional reason, 

 that fossils derived from the Pliocene sandstone of the vicinity are in 

 places included in it. In the lower course of White creek the gravelly 

 bed is at present imdergoing the process of hardening, the evaporating 

 water leaving a white coating on the pebbles that causes them to adhere 

 slightly and part with a harsh sound when one crunches the gravel under 

 foot. 



