MARK TWAIN.--Pursuant to contract, Mark Twain delivered his announced lecture at the Opera House last night, to a very large and fashionable audience of ladies and gentlemen. The lecture is worth hearing. It is more--a rare treat to any one conversant with the history of ancient countries. From the moment the lecturer leaves some very commonplace strictures upon the unfortunate sea-sick pilgrims and Puritans, and commences to relate his experiences of the journey from Gibraltar to the Pyramids; from Spain to Russia; from Syria to the Bosphorus; it is all interesting, instructive, and at times immensely amusing. His power of language-painting is great, and his half soliloquy as to forgetfulness of renowned places where the Quaker City party pressed unappreciative (apparently) feet far exceeds any effort previously made in the poetic line by him who is better known in his writings as a humorist. In brief, we were immensely entertained by the lecture, and pleased, taking hearty applause or laughter as a standard for judgment. To-night the lecture will be repeated at the Opera House, and to-morrow night Mark will speak at Carson. We cheerfully commend him to all desirous of a real, live, entertaining literary treat.