74 The American Geohxjist. Autrust, 1897 
measures of England: but it will be difflcuU for any one who 
examines the order of superposition find the structure and 
composition of the rocks themselves to support such an 
opinion." 
The Carboniferous rocks in the area in which be studied 
them present strong schistose and gneissoid phases, in places 
quite as well marked as in the region of his primary group. 
Crystals of garnet, andalusite, ottrelite, magnetite, and other 
metamorphic minerals, the most significant of which were ob- 
served by him, distinguished the matrix of these plant-bearing 
strata in a marked w^ay from the coal fields of the standard 
sections. Because they were metamorphosed, he believed 
the rocks to be older than the Carboniferous of Europe, Had 
he seen the Massachusetts extension of these rocks, he would 
have found less evidence of this change. 
But whatever bias Jackson may have displayed in crediting 
to mineralogic features values which he denied to biologic 
evidence as indices of relative age, he evinced a keen sense of 
the local geologic conditions. His understanding of the struct- 
iire of the highly folded and metamorphosed rocks of the Car- 
boniferous in Rhode Island has for half a century been little 
improved on by others. 
He seems to have considered a numerical division of the 
groups of strata preferable to "any of those fanciful names" 
which took the place of Werner's Transition series. "It is 
evident," he adds to this expression of his choice, "that the 
names Cambrian and Silurian proposed for certain groups in 
England, will never be regarded in this country, as appropri- 
ate terms for our rocks." The old name was good enough for 
him, and so he wrote, "I therefore adhere to the name Transi- 
tion as original!}^ applied." 
Though primarily an investigator. Jackson was at the same 
time and in his own way a teacher. The introductions to his 
reports are brief text-books of the science as he understood it. 
Even the pedagogical question of the order of presentation of 
geologic phenomena is debated with the reader, and in op- 
position to the then prevalent practice of English geologists of 
beginning with the phenomena of to-day-and going dow-n ward 
in the rock history, he insists on the advantage of the ascend- 
ing order, inasmuch as it sets forth the antecedent circum- 
