Street Improvement — Authority op Supervisors — Delegation op Power.—The board of supervisors of the city and county of San Francisco has exclusive authority for the improvement of its streets, and has no power to delegate authority to the superintendent of streets to determine the necessity of making any improvement in whole or in part, or the character or extent of any improvement which it may itself direct to he made.

Id.—Construction op Sewers—Void Resolution op Intention—Specifications op City Engineer—Discretion op Superintendent.—A resolution of intention to construct sewers upon certain designated streets, according to the plans and specifications prepared by the city-engineer, which contain provisions and conditions which are not determined by the supervisors, but are left to the discretion of the superintendent of streets, without any fixed rules to control his discretion, is void, and no lien can be created under it.

Id.—Power to Determine Amount op Assessment—Expense op Improvement—Delegation op Power.—The legislative body must deteimine not only the character and extent of the improvement to be made, but also the amount of the burden which is to he imposed by assessment upon the adjacent property, to defray the expense of the improvement; and, after the improvement has been ordered, the actual expense must be approved by the legislative body, and fixed in the contract for doing the work as the data upon which the assessment is to he calculated, and no part of the assessment, or of the power to determine the actual expense of the improvement, can he delegated to the superintendent of streets.

Id.—Invalid Lien—Clodd upon Title—Equity—Depense.—An action may be maintained by the owner of property subject to an invalid street assessment to have it adjudged invalid, where there is nothing upon the face of the assessment to show that the lien is not valid, and where, by reason of matters outside of the assessment as it is recorded, the apparent lien may be shown not to be a valid encumbrance; in such ease the assessment constitutes a cloud upon the title, which the property owner is entitled to have removed by a court of equity, although the same matters may be asserted as a defense to an action for the enforcement of the assessment.