Each county surveyor, after being duly qualified as provided in the foregoing section, may appoint such number of deputy surveyors under him as he may think proper, being responsible for the correctness of their official acts, which deputies shall, respectively, before they enter upon the duties of their office, take a similar oath or affirmation to that required of the county surveyor; and all official duties performed and surveys made by a deputy surveyor shall be signed by him officially, and shall be as good and valid in every respect as if the same had been done by the county surveyor.