Eaton’s Key. 69 
evidence of changes and catastrophes, whose history is to be 
sought in the memorials entombed in the strata themselves. 
ive no opinion regarding the theories of Professor 
Mitchill, not intending to review the work, but merely to aid, 
as far asin our power, in drawing the public attention to the 
interesting subjects abeut which it is occupied. 
If we have any remark to add, it is, that an adherence to 
the technical precision with which most rocks are at the pre- 
sent day described, appears desirable in mineralogical and geo- 
logical descriptions. When in the valuable additions before 
us we read of schorl rock, we gain only the idea of a reck con- 
taining that mineral ; but as it occurs occasionally in several of 
the primitive rocks, we are ata loss which is intended; we 
believe it never forms a rock by itself. So with the slate 
rocks ; there are several varieties of them—mica slate, clay 
__ Slate, greenstone slate, d&c. besides some subdivisions ; and the 
mere word slate, does not always give us the precise idea. 
But we are aware that, in the present case, it was less in view 
to go into all the details of geological description, than to give 
a view of our organized remains and of their supposed origin. 
Arr. XII. Notice of Eaton’s Index to the Geology of the 
Northern States, with a Transverse Section of them from 
Catskill Mountain to the Atlantic. 
Te extensive collection of facts in this little book of fifty- 
four pages, is creditable to the author’s industry and discern- 
ment: he informs us that he has travelled 1,000 miles on foot, 
while investigating the geology of the district concerning which 
'e has written. This district is certainly interesting, and 
every attempt to diffuse correct information concerning it, 
deserves encouragement. Mr. Eaton’s account of the regions — 
he has explored, has every mark of verisimilitude ; and we 
commend his efforts to diffuse geological information, by short 
“ourses of lectures, in different towns. In his arrangement of 
rocks, he has deviated from Werner—has adopted some views 
