122 Chronicles of Science. [Jan. 
do the imperfectness of the animal series, and the superior organization 
and degrees of development of the fossil genera and species met with 
in the lowest of the palwozoic rocks, as they are at present restricted 
in their downward horizons, militate against such a view by indicating 
the previous existence of zones of previous creations, and causing the 
reflective mind to regard these earliest paleeozoic fossils as only the 
shreds and patches of still earlier life-garments of our earth, but they 
seem also to make the inquiry lack the aid of the chemist and mine- 
ralogist to tell us whether, in the present altered state of such rock- 
masses as are older than the paleeozoic beds, there can be detected in 
the component materials any ingredients which owe their piesence to 
the former existence in those masses of organic remains. 
It is exactly with this question that Mr. Sterry Hunt has occupied 
himself, and has made some excellent attempts to ascertain whether, 
in the absence of organic remains, or of stratigraphical evidence, there 
are any means of determining, even approximately, the geological 
age of a given series of crystalline stratified rocks—in other words, 
whether the chemical conditions which have presided over the forma- 
tion of sedimentary rocks have so far varied, in the course of ages, as 
to impress upon such rocks any marked chemical and mineralogical 
differences. 'To some extent it does appear possible to work out such 
a problem in respect to definite cases, although as yet no one could 
see the way to the generalization of a rule ; indeed, in the ever-variable 
and divergent conditions of our planet’s surface, and the different 
combinations and oppositions of the atmospheric influences which 
have been, through all periods, carrying on their effects around it 
everywhere, it seems impossible this ever should be accomplished. 'To 
arrive at any such indicative result in the case of unaltered sedimen- 
tary formations could not be accomplished without multiplied analyses, 
and even then the conclusions might not be absolute. It is different, 
however, when chemical or mineralogical changes have set in, for the 
natural ‘affinities of some elements for others render definite the 
results of such combinations, and so we find that the crystalline 
minerals which are formed are definite in their composition, and vary 
with the chemical constitution of the sediment from which they were 
derived. Therefore it is that Mr. Sterry Hunt thinks these crystalline 
minerals of the metamorphosed rocks may become to a considerable 
extent, to the geologist, what organic remains in the unaltered rock 
are to the paleontologist—a guide to geological age and succession. 
The feldspars, for example, composed mainly of silica and alumina, 
combined with the silicates of potash, soda, and lime, do, in their 
spontaneous decomposition, part with the latter ingredients, and there 
remains behind, as a final result, a hydrous silicate of alumina, which 
is kaolin, or clay. Now, where potash and soda feldspars are asso- 
ciated, it has been repeatedly observed that the soda-compound is 
much more readily decomposed than the potash-compound, and that 
the soda-feldspar becomes perfectly friable, and fit for a further reduc- 
tion into clay before the orthoclase, or potash-feldspar, has been altered 
at all. The result of combined chemical and mechanical agencies 
acting upon rocks containing quartz, with orthoclase and such soda- 
