54 PATAGONIAN EXPEDITIONS : NARRATIVE. 



across the river and away to the south over the low plain which stretches 

 for miles toward the eastern entrance to the Straits of Magellan, the enor- 

 mous amount of destruction already accomplished was apparent. The 

 very magnitude of the scale upon which the work was being accomplished 

 commanded admiration, but after all, was there not a certain resemblance 

 between this constructive and destructive work of nature and that of the 

 speculative sciences, where old theories promulgated after long and patient 

 research are for a time accepted as truth, only to be demolished later by 

 the discovery of new facts ? 



Turning to the fossil remains about me, it was evident not only that 

 they all belonged to species long since extinct, but that many of them 

 had left no descendants. As I drew a mental picture of the physical con- 

 ditions of this region in those remote times, when these animals roamed 

 over, lived, died and left their bones on the uplands to bleach and be 

 consumed, or in the lowlands to be preserved in the muds and sands 

 about the shores, over the flood-plains, or in the bottoms of the rivers, 

 lakes and marshes, I could not help wondering what had caused the ex- 

 termination of this great fauna. As I examined the remains of Icochilus, 

 Nesodon, and Prothylacimis that lay before me, they appeared well adapted 

 for maintaining themselves even under the semi-arid conditions at pres- 

 ent prevailing. The first two are supplied with incisor teeth which must 

 have been very efficient in cropping even the shortest grasses, while the 

 molars were admirably adapted for masticating purposes. As a carnivore 

 Prothylacimis would appear well equipped for sustaining itself. Was 

 their extermination due to a certain lack of vitality inherent in the differ- 

 ent genera and families, whereby they became extinct through a want of 

 fertility due to decreased vitality? In other words, does a species, genus, 

 or family, like the individual, pass through the different stages known as 

 birth, youth, maturity, old age and death, regardless of environment, 

 which may accelerate or retard, but cannot prevent, in the former case any 

 more than in the latter,' the final dissolution, no matter how congenial the 

 environment may be ? Or was their extermination due to some great 

 calamity which overtook them, perhaps suddenly, when at the zenith of 

 their development ? It is perhaps more likely that their extermination 

 was due to gradually changing physical conditions, resulting in changes 

 of climate, vegetation, distribution of land and water and other environ- 

 mental conditions, to which they were unable to adapt themselves. 



