INTRODUCTION. 



My connection with the thalassographic work of the Coast 

 Survey dates back to 1849, when, as a boy, I accompanied Pro- 

 fessor Agassiz in his cruise on the " Bibb " off Nantucket, and 

 afterward, in 1851, served as aid on his survey of the Florida 

 Reef. More than twenty years later I returned to this line of 

 study, in a report on a part of the collections made by Pourtales 

 in the " Bibb " in deep water in 1867-68, and since that time I 

 have been engaged, with little interruption, more or less directly 

 in deep-sea work. It was therefore natural that I should accept 

 the invitation given me in 1877, by Mr. Patterson, the Superin- 

 tendent of the Coast Survey, to continue, under its auspices, the 

 work in which I had begun my biological studies. If at times 

 the physical difficulties encountered were somewhat discour- 

 aging, it was a great pleasure to find that my professional train- 

 ing as an engineer not only contributed in no small measure to 

 the success of the expedition, but also increased my interest 

 in the many problems of deep-sea explorations. 



The field of work opened to naturalists by thalassographic 

 surveys is of the greatest importance. The materials collected 

 throw a flood of hght on our knowledge of the conditions of 

 animal life in deep water, and promise the most important gen- 

 eral conclusions on terrestrial physics and on geology. Fasci- 

 nating as has always been the study of marine life, this interest 

 has greatly increased since we have found the means of reach- 

 ing the abyssal fauna. Light has suddenly been shed on many 

 vexed problems concerning the geographical distribution of 

 animals and plants and their succession in time from former 

 geological periods to the present day. New notions of geologi- 



