90 GEOLOGY. 



which it is employed, however, it has little to recommend it on the score of neatness, presenting 

 under a hot sun a constant dripping from the eaves, disagreeable to the smell, and disastrous in 

 its effects on broadcloth and beaver. At the same time, becoming thin, it requires frequent 

 re-application, and in the cold rainy season is liable to crack, giving rise to sudden leaks. An 

 improvement in these respects might doubtlessly be made, by forming a mixture with some 

 other material, which may serve to add to its solidity without impairing its useful retentive 

 properties. The material might also be used in many places in the construction of aqueous 

 reservoirs, for retaining the product of rains during the wet season. These being located at 

 sufficient height to serve the purposes of irrigation, might thus be made the means of redeeming 

 valuable tracts of land from sterility. 



Still further, as an ingredient in the manufacture of sun-dried brick, it promises to come into 

 extensive use, furnishing, at the same time, an almost imperishable article, and admitting of 

 extended useful application in the construction of buildings and fences, with a great saving of 

 bulk of material as compared with the old fashioned " adobe." 



In collecting this mineral bitumen for the uses above enumerated, pits of greater or less depth 

 are sunk in the vicinity of the bitumen springs, to which the issue is conducted. This becoming 

 hardened by exposure to the atmosphere, acquires sufficient solidity in cold weather to render it 

 fit for transportation. 



Connected, probably, with the same bituminous formation, we find frequently exposed in the 

 sides of ocean blufis irregular seams of lignite associated with the sands and clays of the Tertiary 

 deposites. 



The purer forms of this mineral, at times, closely resemble in external character the bitumens 

 above mentioned, though having a more distinct mineralized structure. It is usually associated 

 with clayey shales more or less bituminous, and frequently marked with obscure vegetable 

 impressions. Fossil remains of lizard's teeth are also, according to the examination of Dr. 

 J. L. Le Conte, found associated with this formation. The lignite never shows itself in any 

 abundance, and neither the article itself or the character of the strata would warrant us in 

 regarding it of any economical importance. 



It is to this source that most of the reports of the existence of coal in the vicinity of San Diego 

 have been referred ; a brief statement of the above facts is sufficient to show their unfounded 

 character. 



The general appearance of this lignite formation, in reference to the commonly associated 

 strata and their comparative thickness, is represented in the accompanying sectional sketch o^ 

 Lignite bluf, as seen at the mouth of Solidad valley, above San Diego. — (See section, fig. 162.) 



A third mineral product pertaining to the Tertiary formation, on the coast, is " a highly 

 aggregated calcareous deposit, resembling chalk;" this article is found not generally dis- 

 tributed, but in irregular beds, sometimes of considerable thickness. In the absence of all 

 other limestone materials, it is used for conversion into a weak form of quick-lime ; and it is 

 also from some other associated alkaline properties employed in the making of soap. 



In the tertiary formation on the eastern side of the main mountain range, the only mineral 

 productions worthy of note are gypsum and common salt. The former is quite abundantly 

 exposed in the marl strata, near the mountain base, where it may probably be found to form 



