Stone or burr brick and slag?

In previous posts I have talked about the use of burr brick (overburnt vitrified brick) and slag to decorate the garden at Honeywood. The use of industrial waste for garden decoration has got a very long history. The early 17th century grotto at Skipton Castle in Yorkshire is partly decorated with what is said to volcanic rock but looks to me suspiciously like the slag from local lead smelting works. Glass waste and slag were used to decorate the grotto in Carshalton Park. This was built about 1724 but it is not clear whether the decorative materials were original or an addition.
 
In the 19th century there was a trend towards the use of natural rock in garden decoration. The discovery of Portland cement also allowed various imitation rocks to be made. This was accompanied by a slowly increasing interest in Alpine plants. Natural rock was expensive so its use, on any significant scale, was limited to the very well off. Alfred Smee used it at The Grange in Wallington in the 1860s and William Mallinson, who owned the house in the early 20th century, brought more onto the site. Sir Samuel Barrow also used natural stone in the rockery at The Grove by Carshalton Ponds. The yellow or brown sandstone in these gardens was quarried in the ridge of hills that runs down the centre of the Weald in Surrey, Sussex and Kent.
 
In the 1870s John Ruskin imported stone from the Lake District to decorate the edges of Margaret’s Pool behind Honeywood.

Margaret’s Pool at the corner of West Street and Pound Street. The undeveloped state of the vegetation suggests that this photo may have been taken soon after Ruskin’s work on the pool.

This stone would have been quarried, carted to a railway, loaded onto wagons, and brought to the goods yard at either Wallington or Hackbridge. It then had to be unloaded and carted to site. A large bill was inevitable.

In the 19th and early 20th century there seems to have been a parallel tradition of using cheaper decorative materials such as overburnt brick and slag which could be obtained fairly locally.
 
When John Pattinson Kirk died in 1913 he left £27,275 18s to his adopted daughter Lily. A very substantial sum when you consider that Honeywood was worth about £2,000 in 1939. Kirk and his family were clearly very well off but they still did not use stone to decorate the garden.
 
By the end of the 19th century the use of industrial materials for decoration seems to have been looked down on – at least by some. Charles Thonger’s The Book of Rock and Water Gardens (1907) offered a clear view:

So many miserable failures are everywhere apparent that we may at least know what to avoid. From the small clinker built mounds, hideously studded with shells, which may be seen in those piteous little gardens of the slums, to the vast heaps of vitrified rubbish, which in certain public parks pass for rock gardens, there is a lesson to be learned from all... Why, then, the monotony of these mounds and banks of slag and scoriae, on which only dusty Ivy and rampant Vinca seem to thrive?
 
It seems that, at Honeywood, the Kirks had different views.
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There is a very interesting paper, The British rock garden in the twentieth century by B Elliot, to be found on the RHS website here.