Contempora- 
neous Veins, 
&e. 
168 Professor SEDGWICK on the 
The Whin-Sill rarely contains spangles of iron pyrites. It 
is sometimes traversed by thin, and probably contemporaneous 
veins of carbonate of lime; but I did not find a single example 
of amygdaloidal concretions of that mineral, such as are seen in 
the dyke of Cockfield Fell. Large veins, containing sulphate of 
barytes, blende, galena, and other minerals, pass through the rock 
in one or two places; but they are of a different class from the 
former, and belong to the great metalliferous veins which tra- 
verse all the strata of the country. Such appear to be the prin- 
cipal facts connected with the structure of the great Whin-Sill 
in the district here described *. 
Coatham Stob, contain a considerable quantity of olivine. As I did not discover any trace 
of this mineral in High Teesdale, and as I have not found it in any of the dykes in the North 
of England, which I have since examined, I am disposed to believe, that, in consequence 
of having acted with the blowpipe on over-large fragments, I may have concluded erro- 
neously, that the olive-coloured grains of the decomposing trap of Coatham Stob were 
infusible; and on that account, I may have mistaken granular decomposing pyroxene for 
olivine. 
* While this Paper was passing through the press, I received from Mr. W. Phillips, the 
result of his examination of some specimens of trap rocks derived from the districts described 
in this and in my preceding Paper. I select from his descriptions, those which bear on 
the present subject. 
No. 1. (From High Teesdale,) contains augite with yellow iron pyrites—the white and 
grey specks not probably felspar, for they immediately pass into a white powder under the 
point of the knife. 
No. 2. (From High Teesdale,) same structure with the preceding, and includes minute 
octohedrons of oxidulous iron. The light grey substance is soft and granular. 
No. 3. One of the varieties (from High Teesdale) with large crystals of augite. In 
it is a greyish or yellowish substance, which is translucent, or even transparent, which 
has cleavages, but not sufficiently brilliant for the goniometer. The substance cannot be 
feldspar, because it crumbles, with a moderate pressure, into a grey powder, and its trans- 
lucency, and even transparency, proves that it cannot be in a state of decomposition. 
In the greyish white granular or earthy substance, derived from one specimen, Mr. Phil- 
lips discovered, by help of a glass, very numerous minute slender crystals, which were colour- 
less, and from their form and hardness, appeared to be feldspar. In none of the specimens, 
did he discover any hornblende. In two specimens, one taken from the basaltic dyke 
of Lower Teesdale, and the other taken from a similar dyke at Coley Hill, near Newcastle, he 
discovered well defined crystals of cleavelandite. The reader will remember, that when 
my preceding Paper was written, this mineral had not been separated from feldspar. 
