This is the best explanation of the North American Act,1857:
British North America Act, 1867
This legislation, passed by the British Parliament, created Canada as a new, domestically self-governing federation, consisting of the provinces of New Brunswick, Nova Scotia, Ontario and Quebec, on July 1, 1867. The British North America Act (now the Constitution Act) established the new federation’s distribution of responsibilities and powers for each level of government and the rights of its inhabitants.