Treaty of Concordia

The Treaty of Concordia, or the Partition Treaty of 1648, was signed on March 23, 1648 between the Kingdom of France and the Dutch Republic and divided the island of Saint Martin.
Signature.
The treaty was signed by the two governors of the island, Robert de Longvilliers for France and Martin Thomas for the States General of the Netherlands.
The signing took place atop "Mount Concordia". 
Based on the terms of the agreement, the island of Saint Martin was to be divided between the Kingdom of France and the Dutch Republic, and the peoples of St. Martin were to co-exist co-operatively.
The French would keep the area that they occupied and the coast facing Anguilla, and the Dutch would have the area of the fort and the land around it on the south coast.
The inhabitants would share the natural resources of the island.
However, France and the Netherlands continued to dispute over the ownership of the island until 1817, when the borders of the island were finally set.
See the (Wikisource : English translation of the original text in French).
Validity.
Questions as to its validity have arisen several times in the past and continue to cause issues. Research was supposed to be undertaken by the French Ministry of Foreign Affairs about it.
At the time of the treaty, agreements signed between representatives of the monarch had to be registered at the King's Council. That essential formality was never performed, but it seems that on many occasions, French civil law recognised the validity of the agreement.
The treaty has always been fairly applied in practice and is referred to in the following texts: