Traveling round northern Lancashire and southern Cumbria you may come across tower like stone structures with an arch at the base at the side of a road.  These are Limekilns.  Limekilns were used to create an alkaline powder called quicklime which could be added to soil to reduce the acidity and hence increase the fertility of the land. 
Limekilns are found in northern Lancashire and southern Cumbria because they are close to the source of the materials needed for the process: Carboniferous Limestone and coal.
The kilns are usually built into the side of a hill so the broken up lumps of Limestone could be hauled up to the top of the kiln in a cart and dropped into the top of the oven.  Alternating layers of coal and limestone could be dropped into the top of the kiln enabling a continuous firing process. 

As the two materials burned the ash fell though a grate in the bottom of the kiln and it is this ash that was then used on the land or used to create limewash paints.

The kilns are usually found at the sides of the roads or by canals so that the coal could quickly be brought in and the quicklime taken away.  In the late 19th century, improvements in the process of creating quicklime meant the building fell out of use.

At the time of writing, more information on Limestone Kilns can be found in leaflets available from the Lancaster City Museum including grid references to many of the sites.