Imagine men toiling. Hard at work extracting gypsum. This is Entrée en cavage de haute masse.
Entrée en cavage de haute masse is an entrance to underground quarries. This entrance gave access to the high mass. The high mass is the thickest layer of gypsum.
Gypsum is a sedimentary rock. It formed from the evaporation of seawater. This left salt deposits behind. Over millions of years, these deposits compacted and crystallized. This formed gypsum. The gypse is separated by layers of marl.
Around Paris, the gypsum is divided into several layers. These are called masses. The high mass is the highest. It is also the thickest. For this reason, it was mined the most. It measures 15 to 20 meters thick. The medium mass is about 5 to 7 meters high. The low masses have alternating layers of gypsum. They also contain clay and marl. They are about 12 meters thick.
The fragility of gypsum led to many accidents. One accident in 1778 killed seven people. This led to many regulations. Regulations were put in place regarding the prohibition of gypsum extraction.
At Entrée en cavage de haute masse, miners used picks to extract the gypsum. They created galleries with trapezoidal sections. They used coins or levers to lift each layer. Sometimes they used mines with explosives. Gypsum was for plaster production. It did not need the same precautions as building stone extraction.
The extraction started at the top of the gallery. This was called the “four”. It was hot in the four. Miners removed material using wheelbarrows or wagons. Horses pulled the wagons after the 19th century.
In 1810, a decree allowed gypsum mining to resume. A decree in 1813 controlled the mining very strictly. This was to ensure the safety of the miners. It was also to ensure the stability of the site.
Mines with low covering had to be exploited from open-air mines. Masses with a great thickness could be exploited by pits.
In 1780, a declaration ordered a survey of the mines’ interior. If there was danger, the declaration ordered the destruction of the gypsum mines.
Gypsum extraction around Paris ended between 1860 and 1870. The annexation of Montmartre and other areas to Paris in 1860 caused this. A decree prohibited gypsum mining in Paris.
The high mass entrance shows where miners once accessed the gypsum. It is a reminder of the industry that once thrived here. They extracted gypsum to make plaster. Plaster was used in construction and art. The extraction of gypsum has shaped the landscape of Paris. Now you know the history of the Entrée en cavage de haute masse.