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Geologica’ Systems—Geological Maps, Se. 253 
Anr. VIL.—Geological Systems.— Geological Maps.— Cha- 
 toyant Feldspar. : 
Extracts of letters to the Editor, dated at Paris January 10, 
and March 14, from William Maclure, P. A. N. S. and 
eA, GS. 
Your observation that some subdivision in the nothenela- 
ture of rocks would be useful to geology, is perfectly just, 
although I doubt whether our present knowledge is adequate 
to it Were we to judge by the diluvial and tertiary, these 
doubts may perhaps be confirmed. The first is a division of 
the alluvial class, without any distinct line of boundaries. 
Whether a hill of sand, gravel, or clay, has been aggregated 
by gravitation, from deep, still water, as a sea, lake, flood, &c. 
which they wish to call diluvial, or thrown together by the 
action of a river, or the waves of the sea-shore, which they 
wish to call alluvial, is almost impossible to distinguish; for 
in both cases, the mass stil] remains a bed of sand, gravel, or 
clay. The terrain de transporte of the French geologists, 
applied to all rocks whose parts are rounded by attrition, in- 
cludes almost the whole of Werner’s alluvial. The tertiary, 
including all rocks above the chalk, applies exactly to the 
basin between France and England, from which the name 
was perhaps derived, but cannot well define a geological po- 
sition where no chalk has been found. oi ce s 
ne may perhaps be warranted in supposing the existence 
of a period, when there was, on the surface of the earth, only 
ihe primitive, the oldest of the five classes of Werner’s, the 
other four classes appearing to be formed by fire, water, &c. 
out of the materials composing this first and most ancient 
class. As we have not yet seen the laws of nature actually 
operating, to form any rocks similar to the primitive, we are 
left to conjecture the mode of formation ; the total absence of 
organic remains would lead to the supposition that it was con- 
structed before their existence; the organic remains, and a 
structure in the rocks similar to that which is actually exposed 
to the evidence’of our senses, warrants the supposition, that 
the four other classes were formed at some period in the pro- 
gress of time. The primitive and transition have a fixed cha+ 
racter of universal origin in all parts of the globe where they 
ure found: they have a regularity of stratification, inclination, 
