338 THE JOURNAL OF GEOLOGY. 
and taught his students that they need not go to distant parts of 
the earth to make geological observations, for they could find 
material sufficient for study at their own door. The trap ridges, 
kettle holes and bowlder trains of the vicinity of New Haven 
have thus become of classic interest, not because they presented 
any unusual features, but because Professor Dana resided near 
them, studied them, and gave to the world the results of his 
observations. : 
No operation that was carried on within the range of his 
observation, the details of which could add to the sum of geo- 
logical knowledge or help solve any of its problems, seemed to 
escape his notice. Every railroad: cut, every survey, every 
excavation and every boring he carefully watched and gained 
from them facts which helped him interpret the past history of 
the earth. 
The bricks which were burned in the Quinnipiac kilns he 
had analyzed in order to learn why they fused so easily, and 
gained thereby important information regarding the source of 
the clay. By the dolomitic blocks of the State House he illus- 
trated to his classes the principles of the disintegration of lme- 
stone, and by the granite pillars of the Peabody Museum the 
expansion of stone by heat. From watching the drying of a 
drop of milk on a stone floor he derived an explanation of the 
forms produced by concretionary consolidation, and by experi- 
menting with varieties of sand dropped about an upright darn- 
ing needle established the principles governing the angle of rest 
for falling detritus. 
His ability to retain in his mind various phases of geological 
evidence, and develop them as time progressed, was likewise 
remarkable. Thus, in 1889, in his teaching he laid much more 
stress on the influence of the Cincinnati uplift in determining the 
character of the rocks of the interior of the continent than he 
had previously done in his Manual, for he said he had never 
so fully realized its importance as he had that year. 
Nor were his students compelled to receive obsolete theories 
or time-worn illustrations because he had held or used them 
