Sentence:  As a vast herd of cows in a rich farmer's yard, if, while they are milked, they hear their calves at a distance, lamenting the robbery which is then <WSD>committing</WSD>, roar and bellow; so roared forth the Somersetshire mob an hallaloo, made up of almost as many squalls, screams, and other different sounds as there were persons, or indeed passions among them ... 
Meaning of the word marked with <WSD> tags:  To be committed or perpetrated; to take place; to occur.