Geology op Sydney. 
30 
catastrophes are far from uncommon, and modify the 
earth’s surface over large areas. Callao is the northern 
limit of a stretch of country, 2,400 miles long, that has 
been considerably elevated since the advent of man. 
Old sea beaches are found here from 60 to 1,000 
feet above the sea level. We have, besides, in every 
quarter of the globe, active volcanoes sending forth 
masses of molten rock, and showers of dust and ashes. 
Fig. 6. — Microscopi© structure of Sandstone. 
Professor Shaler says : “The notion that the ground is 
naturally steadfast is an error, — an error which arises 
from the incapacity of our senses to appreciate any 
but the most palpable, and at the same time most 
exceptional, of its movements. The idea of terra firma 
belongs to the ancient belief that the earth was the 
centre of the universe. It is, indeed, by their mobility 
that the continents survive the increasing assaults of 
the ocean waves, and the continuous down-wearing 
