xl OBITUARY NOTICES OF MEMBERS DECEASED. 



York was soon to begin. Geological horizons are recognized by their 

 fossil shells, and Lea was thus led to study living moUusks, the better 

 to understand those in the rocks. 



The receipt of some fresh-water mussels, sent by Major Long, 

 of the \J. S. Engineer Corps, then engaged in deepening the Ohio 

 River, was the occasion of Lea's first paper, which was published 

 in the Transactions of this Society for 1827. 



Once attracted to this subject Lea found an inexhaustible field 

 for work. The great river systems of a continent marvelously pro- 

 lific in bivalve mollusks supplied material. Naturalists in all parts 

 of the country sent the species of their localities. His enthusiasm 

 infected others, and from North and South America, India and 

 Australia, material to be worked up poured in. Lea's work on these 

 great collections of fresh-water mollusks form a series of thirteen 

 stately and richl_\- illustrated (juarto volumes, part published by this 

 Society, part by the Academy of Natural Sciences. His last paper 

 appeared in 1876. 



Every man who sets himself the task of cultivating one plot in 

 the field of intellectual endeavor must needs resist the voices calling 

 him to other tasks, lest in scattering his force, he fail of high achieve- 

 ment. Lea published but little outside of his special work. Several 

 ]:)apers dealing with foreign materials included in gems and other 

 crystals, and one notable paper, on the reptilian tracts of the red 

 sandstones of Pennsylvania, were his main digressions. 



In whatever direction, however, his researches led him he was 

 sure to pursue them to a successful end. The value placed upon 

 them by his fellow scientists is sufiicicnlly indicated by the positions 

 of honor to which they called him. 



I venture upon any estimate of the value of Lea's work with hesi- 

 tation, since my own studies have been in a field widely diverse. I 

 can but give the verdict of those competent to judge, whom I have 

 consulted. Lea's work was mainly descriptive. It was the pioneer 

 work in his branch of zoology, breaking path for those who came 

 after. The march of modern zoology could not proceed without 

 such work as his. And it is the honor of this man that his work 

 was well (lone. While investigations growing out of Lea's work 

 may jirove to have what we term "jM-actical"' ap])lications, yet in 



