A nonstop train travels between Pearl River and Hoboken. On its trip south, traveling at a constant speed, it makes it from Pearl River to Hoboken in 1 hour and 6 minutes. On its return trip north, the train increases its speed by 10 miles per hour, and takes 42 minutes to reach Pearl River from Hoboken.

What was the train's original speed (on its trip south) in miles per hour?