Unplumbed definition

Actual or projected routes for telegraph cables across the deep sea have also been sounded with extreme accuracy in many cases; but beyond these lines of sounding the vast spaces of the ocean remain unplumbed save for the rare researches of scientific expeditions, such as those of the " Challenger," the " Valdivia," the " Albatross " and the " Scotia."

While top-end and mid-range are handled well, once again however the lower ends of the sound spectrum are left sadly unplumbed.

But there are also unplumbed depths in the clarity of this writing.