THE 
GEOLOGICAL MAGAZINE. 
NEW SERIES. DECADE II. VOL. VII. 
No. X—OCTOBER, 1880. 
ORIGINAL ARTICLES. 
—— 
I.—Tar Wain Sitti or Teespare, AS AN 'ASSIMILATOR OF THE 
SurrounpinG bens. 
By C. T. Croven, M.A., F.G.S., of H.M. Geological Survey. 
Communicated by permission of the Director-General of the Geological Survey of 
the United Kingdom. 
WISH in the present paper to draw attention to one aspect of 
the Whin Sill specially, viz. its aspect as an assimilater, and 
other interesting points connected with it I shall only mention 
incidentally, as they may arise during our investigation of this aspect. 
Accordingly, I will take it for granted that there can be no doubt 
that the Whin Sill is not really a “sill”? at all, that it is not con- 
temporaneous with the beds among which it lies, but of later date. 
After noticing the changes in its stratigraphical position, its next 
feature that is most likely to strike one is, I think, the general 
absence of signs of accompanying mechanical disturbance. If such 
an immense and irregular mass has been thrust in among the sedi- 
mentary beds, how is it that these beds are not more squeezed and 
faulted and contorted by it ? 
The difficulty is one that strikes all the more intelligent miners 
and geologists of the Dale, and they always bring it forward when 
you are trying to show them that the Whin Sill is not really a sill. 
They know that it is not always on quite the same geological 
horizon, that at one place you can see it resting on a limestone, and 
at another place ona plate bed, but they get out of this by supposing 
that fresh beds have come in between the two places. They have 
the following two propositions presented to them: either the Whin 
1 Perhaps I had better here explain a few North-country words which occur in 
this paper, and which may not be generally known. 
Whin.—Sometimes applied to any very hard bed, as a hard close-grained sand- 
stone, but more especially to hard crystalline rocks, as the Cleveland Basaltic Dyke, 
and the great mass of stratiform Basalt that occurs in the North of England. This 
name perhaps comes from the sound the rock makes when flying off under the hammer. 
Sill.Any bed of rock lying more or less parallel with the neighbouring bed, 
e.g. the ‘‘ Slate Sills’? and the ‘‘ Coal Sills’’ are particular beds of sandstone in the 
Yoredale Series. The word is probably connected with the word ‘‘sole’’ (the sole of 
the foot), and means anything lying flat. 
Plate.—Shale. 
Post.—The horizontal bands in any bed which are prominently developed on 
weathering. ‘There is a limestone in the Yoredale Series called the ‘‘ Single Post”’ 
limestone, and it gets its name from the fact that very commonly it does not show 
any horizontal division lines at all, but remains united in one mass in its whole 
thickness. 
Syke.—A stream, or beck. 
Girdle Beds.—Alternations of thin sandstones and sandy shales. 
DECADE II.—VOL, VII.—NO. X. 28 
