1903 - 4 .] Mr J. G. Goodchild on Intrusive Bocks. 
201 
paper was not allowed to appear in the Quarterly Journal. But 
in the Geological Magazine, decade ii., vol. xii., pp. 434-447 
(October 1880), the substance of that communication appeared 
under the title of “ The Whin Sill of Teesdale as an Assimilator 
of the Surrounding Beds.” Besides the materials collected in the 
field by himself, Mr Clough was able to get corroborative evidence 
in support of his views from Dr James Geikie, Dr Peach, myself, 
and other of his then colleagues. Mr Clough was quite as fully 
aware of the fact as any of his predecessors in the field that 
though the dolerite in question replaces beds of very diverse 
chemical composition, its own mineral constitution remained 
uniform, and he was equally well aware that there is no trace of 
any lithological passage from the country rock to the intruder, or 
vice versa.- To meet this very formidable chemical difficulty, 
which still looms very large indeed in the eyes of cabinet geologists, 
he wrote (p. 442), referring to objections likely to be raised on 
these grounds: “But any force which this objection possesses 
depends upon the assumption, that if sedimentary beds were taken 
up by the Whin, they would remain in it close at hand in their 
original situation, whereas there may have been a very general 
circulation, both on a large scale and molecule by molecule, 
reducing all the parts of the mixture to a general uniformity of 
composition. The very possibility of forming alloys and of 
modifying the properties of metals by adding to them small 
portions of other substances depends upon this principle of 
circulation or diffusion, so that it cannot be said that we are 
without warrant for it.” 
I may add that the paper has always appeared to me to be 
a very valuable one, and that I can adduce abundant corroborative 
evidence in support of the author’s statements of fact, partly from 
a knowledge of the areas adjacent to Teesdale, where similar 
phenomena are seen, and partly from an examination of the part 
of Teesdale referred to, after the Geological Survey map of the 
district was published. 
Again, in Mr Clough’s case, were the facts ignored or explained 
away, apparently on no other ground than that it appeared very 
unlikely that an extensive sheet of dolerite could, by any means, 
eat up large volumes of sandstone without showing a higher silica 
