I might as well have tried to stop an avalanche.

So, making a virtue of necessity, I let her go, thinking that before she reached the top of the lane she would have had quite enough, and I should be able to pull her up without difficulty.
The colts are soon left behind; but we can hear them galloping behind us, and on goes the mare like the wind.

I can now see the end of the lane, and as the great park wall, twelve feet high, looms in sight, the horrible thought flashes on my mind that unless I pull her up we shall both be dashed to pieces; for to turn a sharp corner at the speed we are going is quite out of the question.
I make another effort, sawing the mare's mouth till it bleeds, and tightening the reins till they are fit to break.
All in vain; she puts her head down and gallops on, if possible more madly than before.

Still larger looms that terrible wall; death stares me in the face, and for the first time in my life I undergo the intense agony of mortal terror.
We are now at the end of the lane.

There is one chance only, and that the most desperate, of saving my life.