C.1915. Sidesaddle habits had a dramatic change of style during the teen's era. Although formal
riding habits were still worn for fox hunting and horse shows, less structured informal became popular (note the straw boater hat in the first photo as compared
to the bowler or the top hat worn in previous decades). The jacket has still remained long.
By this time, women could choose to ride sidesaddle or astride
(glass negative photo C.1910), and this choice made women realize that clothes could be comfortable for riding. Although the glass negative photo isn't clear,
the lady riding astride is wearing a split skirt that could be buttoned sideways for sidesaddle riding or in the middle to make trousers for riding. These trends of the 1910's would lead to the comfortable riding clothes of today, although the present day riding habit is still based on Edwardian styles.
(1915 fashion plates from an unknown source, glass negative L. Hidic)