As soon as I reached comparatively level ground I urged my mount into a canter and continued this, where the going permitted, until, close upon dusk, I discovered the point where other tracks joined those of Powell. They were the tracks of unshod ponies, three of them, and the ponies had been galloping.

I couldn't figure out the meaning of it.
"I urged" = I vigorously encouraged

"my mount" = my horse

"a canter" = a medium pace for a horse, faster than walking, but not as fast as galloping
Thank you, Mr Wordy.[F]