Complex sentence: Harmukh was first climbed by the Great Trigonometric Survey, Thomas Montgomerie in 1856 and made the first survey of the Karakoram some to the north, and sketched the two most prominent peaks, labelling them K1 and K2.
Split into simpler sentences: Harmukh was first climbed by members of the Great Trigonometric Survey lead by Thomas Montgomerie in 1856. Montgomerie made the first survey of the Karakoram some to the north, and sketched the two most prominent peaks, labelling them K1 and K2.