Darton, CA is on the Mitcham War Memorial according to Whitehead, but this is possibly a typo. There is a Dalton, C.R., also note that Darton, C.A. is not listed in the Roll of Honour website.
This article from the 1st May 1915 refers to a lieutenant Darton, but doesn’t give his initials.
AN EXPLODED MINE.
LIEUTENANT AND SAPPER LOSE THEIR LIVES AT COLCHESTER.
Lieutenant Darton, 80th Field Company Reserve Section of the Royal Engineers, and a sapper lost their lives on Friday morning Colchester in a gallant attempt rescue, Some tools had been left tho previous day in an exploded mine under a trench, and Friday morning party of sappers went recover them. The first sapper who entered the passage, which was twelve feet underground, came out complaining of dizziness, and warned the rest of the section not to enter, as it was dangerous. Ten minutes later, however, he re-entered it himself. and as he did not return another sapper went after him. He could not see the sapper, whose name is Williams, but could hear him groaning. Sappers Simpson. Scott, and Bullock then went to the rescue of Williams, but all were overcome by gas. Corporal Blyth and another sapper succeeded in getting out all except Williams.
Word was then sent to Lieutenant Darton, who cycled to the spot, and though breathless from his exertions at once entered the mine. He did not return, and several sappers were sent after him. He and Williams wore ultimately brought out unconscious, and though oxygen was administered both died. Sapper Bullock is still in hospital.
Source: Gloucestershire Echo – Saturday 01 May 1915 from the British Newspaper Archive (subscription required)