350 M. L. Agassiz on the Primitive Diversify and 



a deep red, nearly black, but as it had not been bled, this might 

 have made some difference. The intestines I did not see, but 

 was informed they were not of very great bulk and scarcely 

 filled a wheelbarrow. The blubber laid the thickest at the 

 middle of the body, where it was 3 inches in depth. The fore- 

 head under the layer of blubber consisted of a fatty substance 

 very rich in oil ; from it ran a large quantity of pure and limpid 

 oil. A quantity of oil ran from the mouth, and falling on the 

 ground coagulated, and had the appearance of salad oil in a 

 frozen state. 



They were both caught on the 2nd of October, having run 

 ashore within a few hundred yards of each other in Portland 

 Roads ; the calf was first secured. 



Weymouth, Oct. 13, 1854. 



XXXIII. — On the Primitive Diversity and Number of Animals in 

 Geological Times. By L. Agassiz*. 



There is a view genei'ally entertained by naturalists and geolo- 

 gists, that genera and species of animals and plants are far more 

 numerous in the present age of the world than at any previous 

 geological period. This seems to me an entire misconception 

 of the character and diversity of the fossils which have been dis- 

 covered in the different geological formations, and to rest upon 

 estimates which are not made within the same limits and with 

 the same standard. Whenever a comparison of the diversity and 

 number of fossils of any geological period has been made with 

 those of the living animals and plants belonging to the same 

 classes and families, it has been done under the tacit assumption, 

 which seems to me entirely unjustifiable, that the fossils formerly 

 inhabiting our globe are known to the same extent as the animals 

 which live at present upon its surface ; while it should be well 

 understood, that however accurate our knowledge of fossils may 

 be, it has been restricted, for each geological formation, to a few 

 circumscribed areas. Comparisons of fossil with living animals 

 ought, therefore, to be limited to geographical districts corre- 

 sponding in extent to those in which the fossils occur ; or, more 

 properly, a fossil fauna with all its local peculiarities ought to 

 be compai'ed with a corresponding fauna of the present period, 

 and not with all the animals of the same class living at present 

 upon the whole surface of the globe. And when this is done with 

 sufficient care, and proper allowance is made for the limited time 

 during which investigations of fossils have been carried on com- 



* From Silliman's American Journal of Science and Arts for May 1854. 



