376 AUSTRALIA : 



the northern extremity of the chain. Cape York and the 

 adjacent isles are porphyritie, and the islands which traverse 

 the strait in the same line appear to be all composed of 

 granite, sienite, or old metamorphic rocks. A circumstance 

 well worthy of remark is, that to the eastward of this line 

 none of these primitive rocks appear, but low coral isles or 

 coral reefs occupy solely a belt of sea, sixty miles wide, 

 across the mouth of the Strait. To the east of this again 

 all the islands are volcanic, and chiefly composed of lavas. 

 The distinct division by these three belts adds another to the 

 many singularities of this great ocean channel. 



In the foregoing part of this article we have drawn some- 

 what largely upon our readers' attention (perchance also a 

 little on their patience) by the various facts connected with 

 the coral ridges and reefs forming the vast and prolonged 

 line of barrier on the Australian coast. We recur for a short 

 time to the subject; not, however, in relation to particular 

 localities, but to the general history and theory of these coral 

 formations as one of the great physical phenomena of the 

 earth's surface : impressive, moreover, not solely from the 

 enormous magnitude of these animal creations of the Ocean, 

 but also from the index and evidence they afford of past 

 and progressive changes in the level of the solid crust of the 

 globe. In a former article of this Review (on the Voyages 

 of the Adventure and the Beagle), we noticed the striking 

 views as to these coral formations contained in Mr. Darwin's 

 journal of the latter voyage. This eminent naturalist has 

 since published a separate volume, ' On the Structure and 

 Distribution of Coral Reefs,' which we have taken as one of 

 the heads of the present article ; wishing to complete the 

 view of the subject, and seeing that to Mr. Darwin we owe 

 not only the most extensive and exact observations upon it, 

 but also certain general conclusions which are now in pro- 

 gress of adoption by men of science in every country. From 



