GLEANINGS 
IN 
SCIENCE. 
JVo. 24. — December, 1830. 
I— Directions for the Guidance of those desirotts of making Geological 
and Miner alogical Observations. 
[Continued from p. 48.] 
The above divisions, as before mentioned, are to be considered merely conven- 
tional as in the series of rocks, no defined limits can be marked, where the pn 
mary transition , &c. commence and terminate. They refer to the relative ages of 
the rocks as to a series of successive formations, supposed to have taken place by the 
Wernerian theory, which considered granite as the nucleus first formed, n 
L others were Successively deposited from a fluid winch 
tion The discovery of a mass of granite, resting on a bed or shell limestone, at Clin, 
hna in Norway, vvas the first important observation, tending to shew the recent 
dateifsomeofthe granitic masses The firstdeposits were supposed to have taken 
place in an inclined plane, on the slope of the granite ; these formed the transition 
class - the next deposits, more nearly horizontal, formed the secondary ; after these 
beds were deposited, the water or fluid is supposed to have been withdrawn. Many 
difficulties occur in conceiving this inode of formation, particularly in i 'P 
rocks which lie over many of the secondary beds, but are still equally crystalline 
as the 'primitive ,°antl nearly of the same composition. To account for the forma- 
tion oi these rocks, required the supposition of a second temporary inundation 
■ 'lor the first A summary of the various theories or hypothesis which have 
similar to in wh ich the formation of the crust of the 
bee “ W taken XT wSl be found !n the notes to D’Aubuisson’s, -or in other 
earth has ta P » theory, as illustrated by Professor Playfair, was 
works on Geoli thfs country, and admired for the science and ele- 
the most pnerally receded m hl8 “ u ^J’ the conclusions are drawn. Contrary 
gance with which the re aso mng isg formed, or at least to have 
to Werner, it supposes the ^ of the stratified rocks, by its 
appeared on the surface more rece ^ crugt Qf stratified roc ks, 
whldfit has^berefore elevated or’ displaced from the original horizontal position 
wh ch it has tberetore rnstra tified rocks, as the porphyries, greenstones, 
which they occupied. as of a similar origin with 
basalt, obsidian, P ltc,1 * s “ , V f c the ’ se rocks which intersect the strata, accom- 
gramte ; and hence all in the rocks or strata with which 
panied frequently with shifts, slips* 0 f the violence, and the state of 
they came in contact, are explained as^ 0 f various dates, 
pmk^u^the lias, mid ^"wilf * bij 1 o bse iwe\l'J (from* figv^ that 6 *! 
where such dykes have een • terminates on reaching the Magnesian 
« fonued anterior to that bed. Many 
■ This may be true in the of "ivSriiV^olMerve^u^be 
