56 FORMER CURRENT ACTION — TERRACES. 



large scale as to induce the examiner to look upon the whole plain as once an extensive lake, 

 the level of whose waters were then 200 feet above the present level of the plain belo^v. Near 

 the centre of the valley — that is, about twenty-five miles up from the north end of the plain — 

 low sandstone hills run out from the Santa Lucia range into the valley in long promontory 

 ridges, with flat backs, having a slight slope to the plain, (not more than three degrees,) the 

 lower edge for a few hundred yards being perfectly horizontal and covered with loose sandy de- 

 tritus and angular fragments of stone, derived from the strata of the vicinity. A little south of 

 this the centre of the plain is occupied with an elevated mass, wliich leaves a passage round it 

 between the mountains east and west ; on the former side the Santa Maria runs at present ; the 

 latter is not now occupied by any permanent stream. This elevation is steep in the ascent and 

 requires to be gained by following to some distance the winding gashes formed in its soft sides 

 by the waters rolling off the summit. Its height does not exceed 100 feet, perhaps eighty, more 

 correctly. The summit is perfectly flat, in an extended view, and covered with fine sandy clay 

 and angular detritus of the sandstones, with a few red jasper and porphyritic pebbles. The 

 strata of which this elevation is composed are the yellow and brown sandstones found clothing 

 the sides of the San Jose mountains, with the dip of which it corresiJonds, the beds sloping 

 southwest or towards the Santa Lucia range. The width of this elevated flat-topped plain 

 might be about three miles, and the observed length eight to ten ; how much further south it 

 extended there was no means of deciding, as the valley was not traversed further at this point. 

 When examined by entering the valley from the south, several weeks afterwards, at the distance 

 of more than twenty miles it was not possible to distinguish. But judging from the manner in 

 which the surrounding bottom looked, it was conjectured that the southern edge was also sloped 

 down, though not as bluff as the north, which has a slope from 25° to 40°. From the edge, 

 looking for miles, the river could be traced along its eastern margin in the narrow plain be- 

 tween the foot of this insulated elevation and the San Jose mountains, on whose sides, about 

 150 feet up, could be traced extended flattened shoulders of the sandstone, forming terraces, 

 whose level was nearly that of this plain. On looking west to the Santa Lucia, those prolonged 

 spurs, with their terraced edges, corresponded in level with that of the plain under foot, from 

 which it was separated by an excavation or drop in the strata three to four miles wide. 



Here were fine examples of denudation and littoral action. The currents, which denuded the 

 valley to near its present level, left standing in the centre a mass of sandstone rock, the edges of 

 which it wore down on each side to form channels of outlet. It is evident that the soft strata 

 of the San Jose range covered up this valley the depth of fully 100 feet above its present level — 

 that these have been in great part removed, leaving only the insulated mass in the centre of the 

 valley. It is probable this current action was slow and continued, rather than violent and 

 short of duration, since there are no masses of rock scattered about the plain — no large pebbles ; 

 everything indicates a quiet and easy motion, which, while it undermined the strata in some 

 places, and removed them, gently washed and wore them smooth, leaving a beach detritus of 

 fine quartz sand, to which the partially decomposed material of the underlying stratum has been 

 added since. These waters must have stood above 100 feet over the present plain level, and the 

 current probably flowed from north to south, as the southern edges of the elevated mass in the 

 centre is of so steep a grade. 



These are the highest indications of water-current action in this valley ; the lines on the 

 western side have preserved their parallelism with the central island, while on the eastern 

 side the terrace line is somewhat higher up, as if that whole chain had been uplifted since to a 



