1830 .] 
and Mincralogical Observations. 
43 
lar change of tlieir corresponding parts, formerly in contact sideways, or in a ho- 
rizontal direction. The rock also immediately in contact with the dyke, is frequent- 
ly altered ; to all which circumstances attention should be paid, as being curious 
geological facts, which lead to inferences that will be afterwards mentioned. 
A vein may be defined a narrow seam which appears to have been formed in a 
rock or fissure passing through the strata. The depth to which the vein extends 
is quite unknown, and the longitudinal extent can seldom be ascertained. Veins of 
basalt, greenstone, porphyry, and granite, are generally termed dykes. 
The term strata it is unnecessary to define : eminent geologists differ, however, 
as to the thickness which some beds may have to be called strata or masses ; and 
also distinguish fissures parallel to each other, which are found in some rocks, as 
being different from stratification. For these and other minute distinctions, refer- 
ence must be made to the works on geology. 
The outlines of mountains may also be given, and frequently on their sides the 
washing off of the earth lias laid bare a portion of the rocks, which in some cases 
shew the junction of unstratified with stratified rocks, and sometimes veins from, 
the former running into the latter, (as in fig. 4.) 
When the planes of the upper beds are not parallel to the planes of the beds on 
which they rest, they are termed uncojifortnahle, an example of which is seen in the 
figs. 4a, and 7, when the sand and magnesian limestone beds lie on the edge of the 
coal, and seem to indicate different periods of formation, as will be afterwards men- 
tioned. Such instances, when shewn in the above mentioned situations in the ver- 
tical section, should be carefully observed ; or when only in the horizontal junction, 
imeh should be traced along the place with the dips of the strata, as in fig. 1. The 
hips being marked by an arrow with figures to read in its direction, as is done in 
the sketch. 
The organic remains and impressions contained in the strata are of great inter- 
est, but the specimens are generally found in accidental digging, and, at any rate, 
to make a collection would require much time and expense. It will, therefore, be 
considered as desirable, merely to ascertain the beds, and the general nature of the 
remains which they contain, accompanied, when it can be done, with the few spe- 
cimens that can be procured of undoubted authenticity, which can seldom be the 
case with bought specimens. The remains in the solid rocks have been changed in 
their nature, mineralized or petrified. Those in the gravel and sand are but little 
altered; the same with those found inthe peat bogs, as of the gigantic Elk and others. 
When the rocks are worked for economical purposes, as slate, lime, gypsum, 
(plaster of Paris) such should be stated, with some account of their extent or value, 
and the market to which they are sent. 
The names given to the beds by the inhabitants should also be stated, as such 
names have frequently reference to the purposes for which they are used ; as fire- 
stone, from being employed to line furnaces, millstone grit, &c. 
By observing walls and buildings, a knowledge of the nature and durability of the 
rocks, and of their value as stones for building, will be obtained. 
1 lie specimens should be shaped ou the ground, and care taken to get a fresh 
fracture : they should always be labelled or numbered, referring to a descriptive ca- 
talogue, and wrapt up separately in paper, whilst on the ground, to avoid the chance 
of mistake. 
On bringing the specimens home, they should be re-examined and proper labels 
fixed with gum-water. When packed to be sent to any distance, each specimen 
should be in a double paper, and the whole firmly packed together with hay, moss, 
or tow, in a deal box or cask. 
By looking at and examining the specimens, and at the same time referring to the 
works on mineralogy for the character by which they are distinguished, the student 
may, of himself, be enabled to prosecute the subject, and, it is hoped, be induced to 
take an interest in the pursuit. Hardness, according to a certain scale of minerals, 
being one of the chief distinguishing characters employed in the system of Mohs, a 
set of minerals arranged so as to give the means of applying its characteristic, and 
understanding its use, would facilitate his enquiries. The specific gravity can be taken 
with small scales and weights, but the most convenient instrument for a person not 
resident, is a hydrometer, termed Nicholson’s, from the inventor. A goniometer, 
tor measuring the angles of the crystals, will also be required by such as wish to 
pursue the study of mineralogy. 
The minerals forming the great portion of the rocks, are quartz, felspar, horu- 
b ende, mica, augite, limestone or calcareous spar, gypsum, diallage, talc. 
