 By 1893 there were more than 75 collieries within the Rhondda Valleys and although most were initially owned by a small group of private individuals this trend changed towards the start of the 20th century as companies began buying up the existing collieries . The widespread adoption of limited liability status began a trend towards a concentration of ownership , reducing some of the economic risks involved in coalmining : unstable coal prices , inflated acquisitions , geological difficulties , and large scale accidents . The emerging companies were formed by the individuals and families who sank the original collieries ; but by the start of the 20th century , they were no more than principal shareholders . These companies included the Davies 's Ocean Coal Company , Archibald Hood 's Glamorgan Coal Company and David Davis & Son . 
