 As the industrialisation of the valleys began there was little shift in the use of Welsh as a first language . Initial immigrants were Welsh and it was not until the 1900s that English workers began settling in any great numbers , but it wasn 't these new workers who changed the language ; the erosion of Welsh had already begun in the 1860s in the school classrooms . The educational philosophy accepted by schoolmasters and governmental administrators was that English was the language of scholars , and that Welsh was a barrier to moral and commercial prosperity . In 1901 35 @.@ 4 % of Rhondda workers spoke only English but by 1911 this had risen to 43 @.@ 1 % , while Welsh speaking <unk> had dropped from 11 @.@ 4 % to 4 @.@ 4 % in the same period . 
