What does this source tell us about the nature of the iron industry in Merthyr at this time? (sorry source unavailable in electronic form)

This document is a journal of the tour of J H Manners through North and South Wales and was written around the year 1805. He was an English aristocrat who was the youngest son of the Duke of Rutland. Many young men of his age and class would have gone touring in Europe at this time, but due to the wars in France between 1793 and 1815, it made it more advisable to take a tour of Britain …

…An example of this states "In 1748, Viscount Windsor [Who had inherited the Welsh estates of the Earls of Pembroke] granted a 99 year lease of the minerals of the common of the lordship of Senghennydd Uwch Caech to a group of industrialists at the rent of £26 a year". Ultimately, the owners of these works became very rich men. "Cyfarthfa was so successful that Crawshay on his death was one of Britain's first millionaires".