Darwin is describing his very favorable impression of Sydney.
“The roads were excellent, and made upon the MacAdam principle, whinstone having been brought for the purpose from the distance of several miles.”

“55 million years ago during the Tertiary Period, extensive volcanic activity centred on the Isle of Mull, resulted in the intrusion of a series of dykes and sills of molten lava which forced their way upwards through the existing strata. The Easdale slate beds were at this time crossed in a NW to SE direction by one large dyke and several smaller dykes and sills of Dolerite, a hard basaltic granite known locally as Whinstone.”