In addition to working with the literature of others, Darley also wrote (and illustrated) his own book, Sketches Abroad with Pen and Pencil (1868), based on a trip to Europe during the Civil War. Like many other authors, Darley claimed these "sketches" were not intended for publication but for the private circulation of family and friends — until a friend convinced him otherwise. "I was induced to put them into type and use them as a thread whereon to hang the illustrations," many of which he claimed were drawn on trains, steamers, and even on a mule. Darley, in fact, offered that scene both pictorially and in prose. Traveling through Mont Blanc, he had to ride on a mule, "which I found a very hairerecting process." He describes the experience:
I brought up the rear on a critter that looked like an apple on four sticks. The tormenting propensity these creatures have for walking on the outer edge of these mountain passes, is rather alarming to the inexperienced. You sometimes look down, two thousand feet, over your mule's neck, as he turns an angle of the road, into the misty depths below. The view we beheld on reaching the top of La Flegere was glorious! It embraces the entire chain of Mont Blanc, from the Col de Balme to the Glacier des Bossons. Directly opposite were the glittering points of the Aiguilles Vertes, which rose before us like a mighty vision; the clouds floating about their lofty peaks, now shutting them from our sight, and now revealing them, with a strange phosphorescent light playing upon their snow-clad summits, which were dazzling in their splendor.
Though born in Philadelphia, for a time a resident of New York City, and the owner of a home in Delaware, Darley was laid to rest at Mount Auburn Cemetery in Cambridge, Massachusetts, the native town of his wife.