GEOLOGICAL INTRODUCTION. 



BY MR. DARWIN. 



Mr. Owen having undertaken the description of the fossil remains of the Mam- 

 malia, which were collected during the voyage of the Beagle, and which are now 

 deposited in the Museum of the College of Surgeons in London, it remains for 

 me briefly to state the circumstances under which they were discovered. As it 

 would require a lengthened discussion to enter fully on the geological history of 

 the deposits in which these remains have been preserved, and as this will be the 

 subject of a separate work, I shall here only give sufficient details, for the reader to 

 form some general idea of the epoch, at which these animals lived, — of their rela- 

 tive antiquity one to the other,— and of the circumstances under which their 

 skeletons were embedded. All the remains were found between latitudes 31° and 

 50° on the eastern side of South America. The localities may conveniently be 

 classed under three divisions, namely— the Provinces bordering the Plata ; Bahia 

 Blanca situated near the confines of Northern Patagonia; and Southern 

 Patagonia. 



The first division includes an enormous area, abounding with the remains of 

 large animals. To the eastward and southward of the great streams, which unite 

 to form the estuary of the Plata, those almost boundless plains extend, which 

 are known by the name of the Pampas. Their physical constitution does not 

 vary over a wide extent; — the traveller may pass for many hundred miles on a 

 level surface, without meeting with a single pebble, or discovering any change in 



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