COEAL REEFS. 367 



more complex and irregular manner, the free passage from 

 tlie Southern Pacific to the seas of the Indian Archipelago. 

 A moment's inspection of the map will show the singular 

 importance of this Strait to the direct intercourse between 

 our great Australian colonies and India, China, and Europe ; 

 and the value of an accurate survey of its complicated and 

 difficult channels, so strongly enjoined in the Admiralty 

 instructions for Captain Blackwood. It is, indeed, a strange 

 and uncouth passage a labyrinth of coral reefs, volcanic 

 rocks, islets, and shoals yet destined nevertheless to yield 

 that free channel which man requires for his commerce, and 

 which the zeal and boldness of those seeking for it are sure 

 eventually to obtain. 



Having dwelt thus fully on the local circumstances of reef, 

 channels, and sea, which formed the object and guided the 

 direction of Captain Blackwood's survey, we need not pursue 

 the track of his voyages in any minute detail. The actual 

 survey was begun at the end of the year 1842, eight months 

 after his departure from England, and his labours were con- 

 tinued until June, 1845; with intervening periods of 

 repair and repose at different parts of Australia and the 

 Indian Archipelago. These labours, combined with those of 

 Flinders at a prior time, complete the survey of the Great 

 Barrier Reef for a space of nearly a thousand miles, leaving 

 only one short hiatus to be filled up. The examination of 

 the eastern part of Torres Strait, and the channels amidst 

 its reefs, is perhaps the most valuable part of the work ac- 

 complished ; and the charts reduced from the survey will 

 remain as lasting records of it, unless some of those gradual 

 changes on the crust of the globe which geology records 

 or other more violent and sudden convulsions, such as have 

 been frequent among the Indian islands should disturb 

 the coral flooring of these seas, and alter the soundings and 

 channels that have now been explored.^ 



