84 The American Geologist. August, i897 
thoroughly qualified form we know as the doctrine of isos- 
tasy. He recognized the effect of the shifting of load through 
denudation. He supposed that when the ditference of level 
had become sufficiently altered to be adequate to overcome 
the resistance of the eartli's crust a paroxysmal elevation 
might take place, with all the phenomena of an earthquake, 
as happened in China in 1834. 
Occasion has already been found for referring to his meth- 
ods of correlating strata. In all this and what follows, we 
must remember that immense strides have been made in the 
understanding of this problem within the lifetime of the 
younger geologists. Jackson simply reflected the methods of 
others when he was led by a question to state that he "had 
sought carefully for inipressions of rain drops" in the Lake 
Superior sandstones, "for the purpose of identifying the age 
with that of the Connecticut River sandstone, but in vain." 
Metamorphism, if we may accept most of the references he 
makes to the subject as embodjnng his views, is the result of 
igneous action. Yet he thinks hot water under ocean 
pressure a satisfactory explanation of the making of the 
anthracite of Pennsylvania. His explanation of gneiss has 
already been referred to. He did not regard water of cryst- 
allization in igneous rocks as proof of their original sedi- 
mentary condition. Fragments of slates in the granites of 
the White Mountains, he thought to be an occurrence irrecon- 
cilable witli the view that the igneous rock was melted down 
sandstone and slate. His conception of igneous rocks was 
that which is held by the modern petrographer. Jackson be- 
lieved thoroughly in the intrusive origin of these rocks. He 
saw in them no signs of a previous clastic texture or strati- 
tied condition. 
Jackson's laboratory was a well known place. It was one 
of the first if not the first of chemical laboratories in this 
country to receive students. His reverend friend, Dr. Bartol, 
who was a frequent visitor there, tells an anecdote of the 
place. "One day," so Jackson told him, "a countryman came 
in with a handkerchief full of those yellow blocks called iron 
pyrites, saying he had found a gold mine on his farm, and 
would not take no for an answer. The patient chemist held 
some of the little cubes in his shovel over a blazing fire till 
