Wadsworth.] A476 [March 17, 
The jaspilite and ore are found to break in various directions 
across the lamination of the associated rocks, to indurate them at the 
line of junction, to send stringers and tongues into them, to cut the 
laminae in every direction; in short, to behave always like an eruptive 
rock and never like a sedimentary one. No theory of deposition in 
fissures and cavities will account for these relations, since the internal 
structure and contact relations are not such as occur in this case. 
Further, it would be necessary to invert the strata several times in 
order to fill the cavities that exist in the same pit, since they hold 
every relation to the horizon; and lastly it would require the schists 
to be a formation of prior age to the iron ores, one that had been 
deeply buried, metamorphosed, and then elevated before the deposi- 
tion of the latter. 
It seems that Mr. Brooks,a mining engineer, whose authority has 
been generally followed upon the question of the sedimentary origin 
of the jaspilite and ore, found himself obliged to admit that in the 
Lake Superior mine there occurred masses which “ appear like dykes 
of ore, squeezed out of the parent mass, which we may suppose to 
have been in a comparatively plastic state, when the folding took 
place; or they may have been small beds, contained originally in the 
chloritic schist, and brought to their present form and position by the 
same causes which produce the eleavage in the schist.” (Geol. of 
Mich., 1, 139, 140.) We thus see that Mr. Brooks arrived at a point 
where he was compelled to admit that the ore was in dikes, or at 
least had been in a plastic state. He further acknowledges that he is 
“unable to give any intelligent hypothesis of its structure.” It seems 
that the Survey was abandoned at this point, the mines having been 
previously studied which offered the least obvious difficulties in the 
way of his theories. Had his work contipued there is no knowing © 
what views he might have held. 
The efforts to prove the jaspilite and ore to be sedimentary required 
‘the assumption that they have, since deposition, been rendered plas- 
tic, that is have been protruded into other rocks as eruptive rocks are. 
This admission involves certain things that appear not to be well 
established. , | 
1°. We are not aware that it has ever been proved by any accu- 
rate, thorough observations by properly trained observers, that a sed- 
imentary rock has ever been made plastic by natural causes; in other 
words, proof is wanting that a sedimentary rock has ever been found 
with the characters of an eruptive one. The burden of proof yet 
