1871-7^-] LETTER TO h\ PIERCE. 185 



the limits of errors which the imperfection of our knowledge renders 

 unavoidable, be sufficient to foretell what we are likely to find in 

 the deepest abysses of the sea, from which thus far nothing has 

 been secured. 



. . . There is a correlation between the gradation of animals in 

 the complication of their structure, their order of succession in geo- 

 logical times, their mode of development from the egg, and their 

 geographical distribution upon the surface of the globe. If that 

 be so, and if the animal world designed from the beginning has 

 been the motive for the physical changes which our globe has 

 undergone, and if, as I also believe to be the case, these changes 

 have not been the cause of the diversity now observed among 

 organized beings, then we may expect, from the greater depth of 

 the ocean, representatives resembling those types of animals which 

 were prominent in earlier geological periods, or bear a closer 

 resemblance to younger stages of the higher members of the same 

 types, or to the lower forms which take their place nowadays. 



As the adversaries of Agassiz not only sharply criti- 

 cised, but even scouted these views, and cast all manner 

 of fun upon them, and as I made the suggestion to him 

 that successive marine faunas would be found at succes- 

 sive great depths, according to the number of fathoms, 

 showing a correlation between the depth and the geo- 

 logical periods, the deepest possessing forms of the 

 primordial fauna, and consider myself as responsible for 

 it, I would call attention to the following facts, very 

 lately made public. 



This prophetic announcement has been at least fully 

 confirmed in regard to Radiolaria, which have been 

 brought up from great depths, varying from six thou- 

 sand to thirteen thousand metres, and present numer- 

 ous genera absolutely identical with forms existing, not 

 only in the Mesozoic and Palaeozoic strata, but even 



