428 
THE GEOLOGIST. 
to observe the exquisite delicacy of the process by whicb this substitu- 
tion has been effected, the most delicate characters being as perfectly 
preserved as in a living specimen. The preservation of the most 
fragile objects, as delicate shells and stems of corals, is an important 
fact in reference to the process by which they were originally entombed. 
" The relative positions of the stratified and unstratified masses is 
such that, as a general rule, the former reposes on the latter. Ifear 
their surfaces of junction, however, they are frequently dove-tailed, as 
it were, into each other, by veins of the iin stratified mass which pene- 
trate into the stratified portion. In other cases, vertical dyhes rise like 
walls through the strata ; and, in almost every mountainous district, 
similar rocks are found either in large irregular masses, or regularly inter- 
stratified between the beds of stratified rock. These facts are highly 
Bignificant as indicating the primitive state of the unstratified mass. 
" The positions of the strata of the stratified mass next demand our 
attention. We have spoken of them as being in general approximately 
horizontal; but in numerous instances they deviate more or less from 
this position, the deviation being more general in the older strata, and 
usually the greatest in mountainous districts, where the strata become 
not unfrequently nearly vertical. This inclination to the horizon causes 
each stratum to rise successively to the surface, and thus enables us to 
ascertain its mineral nature and organic contents. The angle of incli- 
nation is termed the dip of the beds. It not unfrequently changes from 
one direction to the opposite, several times within the limits of the same 
mountainous district, as shown in the annexed diagram, which repre- 
sents a section in the direction of the dip. Lines through A and B 
AC B 
perpendicular to tlic section are called (tnticlinal lines, and a similar line 
through C is called a synclinal line. Such lines will frequently be con- 
tinuous and nearly straiglit for many miles, and often correspond more 
or less with the external character of the district, in some such manner 
as indicated by the diagram. 
" It is this inclined disposition of the strata whicli enables us to 
form some rude estimate of the thickness of the whole stratified mass in 
particular localities. It cannot, in many places, be estimated at less 
than 20,000 or 30,000 feet, and may possibly be considerably greater. 
It is essential that the geological reader should realize in his own mind 
the enormous magnitude of the stratified and fossiliferous portion of the 
earth's crust. 
" There is another kind of discontinuity to which these strata 
are subject, and which may also be best illustrated by a simple diagram. 
In these cases, the whole stratified mass has the ajjpcarance of having 
been dislocated along the nearly vertical planes d e, as indicated by the 
discontinuous stratum ah h' c. This dislocation is called a fault. The 
