358 
Directions for making Geological 
[Dec. 
of these dykes intersect each other, causing shifts (fig. 2) and slips as they do in 
the strata, which shows their being of different dates with regard to each other. 
In the coal fields of Newcastle the slip accompanying one dyke is so great, that 
the beds on one side of it are 90 fathoms below the same beds on the other side. 
In the section fig. 4, it will be seen, that the beds of the coal measured on one side 
of the dyke, cease to have their planes parallel to the corresponding beds on the 
other side ; from which it must be inferred that the dyke came to occupy the 
fissure, accompanied by some convulsion, as a subsidence of the surface of the right. 
The Wernerian theory considers these veins to have been fissures in the rocks, 
filled from above ; whilst the Huttonian theory considers them to have been filled 
from below, as above stated. The rocks immediately in contact with them are 
frequently changed, as in the coal at Newcastle, which is at, and near the point of 
contact, without bitumen ; and the clay has become so hard as to be used for 
whetstone ; the limestone is also altered, but not decomposed, which was consider- 
ed as conclusive against their having been filled by matter in a state of fusion, 
until the experiment of Sir James Hall, of fusing or melting the carbonate of lime 
(limestone) without driving off the carbonic acid, by retaining the whole hermetically 
sealed whilst in the furnace ; from which it is inferred that limestone may 
be submitted to great heat without altering Its nature, if under sufficient pressure, 
as it would be when at the bottom of the ocean. 
In the metallic veins the same changes of the rocks in contact with them, does not 
appear to be found ; such veins are, however, more confined to the primitive rocks, 
particularly gneis and mica slate, though great part of the lead in England is found in 
veins in the mountain limestone No metallic veins have been found in strata superior 
to the red marl ; these metalliferous veins are, however, sometimes accompanied by 
shifts and slips in the strata through which they pass, similar to what has been men- 
tioned of some of the whin dykes ; but others, and veins of quartz, are considered as 
bearing evidence of being of contemporaneous formation with the nicks in which they 
are found. Others again may be supposed to have been some trifling fissure not ex- 
tending to the surface, which has been filled by infiltration of matter through the 
rocks forming its walls. There are other fissures which hear evidence of having been 
filled from the surface, since they contain fragments of earth, bone, &c. &c. The rock 
of Gibraltar, which is of mountain limestone, is intersected with such veins, contain- 
ing bones, cemented in calcareous spar, or in stalactite. Other fissures, or rather 
openings or holes in the rocks, particularly in limestone, have been found at differ- 
ent places, as in tbe Hartz, Bayreuth , and lately in Yorkshire, which Jed to caves 
containing a great accumulation of bones of various animals, particularly of 
hyaenas and many graminivorous animals, which have caused a considerable inter- 
est and discussion, in tbe endeavour to assign some probable cause which could be 
supposed to have brought them together in such a situation. It is not easy to 
conceive in what manner the fissures or veins in the rock of Gibraltar could be 
filled with bones, but it is considered as pretty satisfactorily established, that the 
caves of Bayreuth and Kirkdale have been the habitations of hyaenas that had 
transported bones to them for their food ; merely the hard portions of the bones 
being found remaining, and these exhibiting the marks of teeth. The papers 
descriptive of the above caves will be found in the Transactions of the Geological 
Society, or in the work of Professor Buckland, termed Reliquice Diluvianar. These 
bones are considered diluvial, or to have belonged to animals existing previously to 
the present state of things. Professor Buckland gives, as a distinguishing characterof 
diluvial from alluvial bones, the adhesion of the former when touched by tbe tongue. 
The different theories above alluded to, led the attention of former Geo- 
logists more particularly to the investigation of the crystalline unstratified rocks, 
and the mode in which they were connected with the stratified at their points of 
junction, in the hopes of arriving at a knowledge of the mode in which that junc- 
tion had happened $ whether by a quiet deposition on the nucleus of granite previ- 
ously formed, as supposed in the one theory, or by having broken through, and 
torn up the strata, as supposed in the other. The spirit with which these inqui- 
ries were pursued led to a knowledge of many important facts, but it may be said 
that none were found to be conclusive in favour of either theory, or'at least other 
observations were made which could not be included under the same explanation, 
and many geologists considered the granite, gneis and slate, as all being of the 
saint! mode of formation, only differing in structure, in consequence of a variation 
in t ic proportion of mica, since their chemical composition is nearly similar. One 
great o lject with the supporters of the Huttonian theory was, to ascertain whether 
> es of granite and greenstone run into the mass of the mountain, losing them* 
