No, cast stone was NOT "...first used extensively in London in the year 1900". You're misinformed. There are many examples of cast stone that predate 1900. For example, one form of cast stone was invented in the UK in 1770 by Mrs. Eleanor Coade, and was already hugely popular by the 1810s (it was extensively used in the 1820s restoration of Buckingham Palace, and those elements survive to this day). "Coade Stone" was first used in the US as early as about 1800 (see Rossborough Inn on the University of Maryland Campus, and John Tayloe's "Octagon House" in Washington DC). The company that developed the secret process for making Coade Stone went out of business in the early-1840s, and those secrets were lost.