32 PICTURESQUE SKETCHES 



going on ; and by similar changes we must account 

 for the presence of lofty masses of solid rock exhibit- 

 ing the remains of the ancient coral polyp in the old 

 rocks. 



The prodigious extent of the combined and uninter- 

 mitting labours of these little world-architects must 

 be witnessed, in order to be adequately conceived or 

 realised. They have built up four hundred miles of 

 barrier reef on the shores of New Caledonia ; and on 

 the north-east coast of Australia their labours extend 

 for one thousand miles in length ; and these reefs may 

 average, perhaps, a quarter of a mile in breadth, and 

 one hundred and fifty feet in depth, and they have 

 been built amidst the waves of the ocean, and in defi- 

 ance of its fiercest storms. The Geologist, in contem- 

 plating these stupendous operations, learns to appre- 

 ciate the circumstances by which were deposited in 

 ancient times, and under other conditions than those 

 which now characterise our climate, those mountain 

 masses of limestone, for the most part entirely co- 

 ralline, which abound in many parts of our native 

 island. The most abundant remains of corals in these 

 masses are similar in their general nature to living 

 species, but indicate animals very distinct from those 

 living polyps which are now actively engaged in form- 

 ing similar deposits on the undulating and half-sub- 

 merged crust of the earth washed by the Indian and 

 Pacific oceans. The limestones, which form a part 

 even of the oldest formations, offer distinct proof, by 

 their organic remains, that they are due to the secre- 

 tions of gelatinous polyps, the species of which perish- 

 ed before those that formed the newer strata were 

 created ; and, as these polyps of the older period have 



