14 



up of fhe same materials as those to the west, but at their southern extremity 

 there is a small out-crop of the primitive rocks. 



These two valleys unite a few miles north of the Guilicus, and are, in fact, but 

 one plain, being divided into two branches by the group of low mountains above 

 alluded to. 



On both flanks of the ridge in the middle of this plain, and at elevations vary 

 ing from two to five hundred feet above the sea, are to be found beds of an 

 infusorial deposit in a fossil state, of considerable thickness. These beds are 

 made up of the siliceous coverings of the Diatomacne principally. On the west 

 flank of the mountain north of Santa Rosa, they extend for a distance of twelve 

 miles, making the entire length of these deposits on this line of ridges about 

 twenty-eight miles. 



Crossing a similar ridge from Sonoma to Napa Valley, which is about twelve 

 miles across, the same deposits are met with on both flanks of the mountain 

 skirting the Napa Valley, and they extend in an easterly direction across the 

 southern spurs of the range to the declivities of the Coast Mountains, forming 

 the west boundaries of the Sacramento Plains, and as far north on that flank as 

 Puta Creek, beyond which point I have, as yet, been unable to trace them. 



This deposit bears the common name of " Chalk Rock " throughout this part 

 of the country. In all the points at which an opportunity has offered for exami 

 nation, these fossil deposits were found reposmg on the primitive series, associated 

 or unassociated with others of the sedimentary group ; in some cases the latter 

 were filled with other marine fossils, but in most instances they were destitute of 

 organic remains. "Nfc i j- 



MINERAL CHARACTER OF THE PRIMITIVE ROCKS OF THE COAST 



MOUNTAINS. 



Among the primitive rocks of the above district the granite series was most 

 predominant. These consisted of coarse granite, mica, schists, sienites, with occa 

 sional patches of the serpentine rocks. The granites w'ere mostly micaceous, and 

 the seams often contained epidote. 



It was a frequent occurrence to find small veins of quartz running through the 

 series in almost every part of it. The drift derived from the breaking down of 

 this series, contains a large proportion of this material, sufficient to attract atten 

 tion in passing over almost any part of these plains. 



Magnetic sand was observed in most of the small streams, and the sulphuret of 

 iron in a few localities. In the vicinity of the Sulphur Springs at the head of 

 Napa Valley, and in the trappean rocks of that district, this latter mineral is abun 

 dant. It is owing to the presence of this mineral at these springs that they de 

 rive their sulphurous odor. 



SOILS OF PETALUMA VALLEY. 



From the character of the rocks above described, and which compose the 

 mountains that surround this and the adjoining valleys, it will be easy to infer the 

 character of a soil derived from such materials. 



Accordingly, we find on most of the lower bottoms, a compost, it might almost 

 be said, that in itself would be adequate to the production of almost any crop that 

 might be placed upon it. In the immediate vicinity of the recent volcanic rocks 

 the soil is soft and mellow, being much superior to that on the bottom lands of 

 the plain. On these bottom lands there is an intimate mixture of the arenaceous 



