Based on 'Rock glazes of NZ'
Sample 25: Dark coarse-grained grit, Greymouth
A dark grey, coarse sandstone or grit showing numerous tiny angular fragments of argillite ( see number 12) set in a fine greyish matrix.
There are a few entries in Bondy's book that are unclear and Greymouth is one. There is no actual description of where the sample was gathered. The Cobden beach recreational area runs alongside the Grey River and the sample I collected was coarse sand from a small beach on the river bank.
I have searched through geology terms and glossary's and grit isn't a reference used. I can only assume that its a gritty substance or grain that isn't as fine as sand. This sample defiantly has numerous grain colours, Perhaps 'set in' refers to the majority being light grey.