Earlier quoted context omitted.
As I noted in the other post, the Big Hole in South Africa was dug to a depth of 240 meters by hand . Coal mines of that depth nothing special, even with 19th Century steam technology. https://en.wikipedia.org/wiki/History_of_coal_mining "By 1856, the average depth in the Borinage was 361 meters (1,184 ft), and in 1866, 437 meters (1,434 ft) and some pits had reached down 700 to 900 meters (2,300 to 3,000 ft); one wa…
"thanks to the good pumping system" (guess what powers that) and "by the late 19th century the seams were becoming exhausted" indicate the practical limitations faced by that.
In the 19th Century?
Steam engines that burn part of the extracted coal. What else?
> by the late 19th century the seams were becoming exhausted
Those particular seams, maybe. They're not the only seams, dude.
I think we're done here.