RASTALL : THE INGLETONIAN SERIES OF W. YORKSHIRE. 97 
that the ground-mass is very fine in texture, thus suggesting 
rhyoHtes rather than hypabyssal intrusives. 
Well-defined lavas are moderately common, and in par- 
ticular two distinctive types may be mentioned. There are 
a fair number of rather large fragments of rhyolites, showing 
in great perfection the peculiar structure known as micropoe- 
cilitic. Others are of a trachytic character, consisting chiefly 
of rather ragged irregular prisms of felspar, which appears to 
be in most cases orthoclase or anorthoclase. One or two ex- 
amples containing a good deal of chlorite are probably referable 
to the andesite group, but basic lavas are apparently absent. 
Taking the igneous rocks as a whole, they appear to belong 
to an alkaline petrographical province, as shown by the common 
occurrence of perthite and the abundance of lavas of trachytic 
appearance, but of course the evidence is insufficient to establish 
this fact with certainty. 
One of the most conspicuous elements of this conglomerate 
is the dark green rock of fine texture which has already been 
briefly referred to. This occurs in large fragments up to a 
foot or more in length, and it shows slight indications of cleavage. 
Both to the naked eye and under the microscope its appearance 
is suggestive of a fine-grained volcanic ash or tuff. I have 
compared it with specimens of pre-Cambrian tuffs in Dr. Bonney's 
collection, and it shows striking resemblances to the hones tones 
of Charnwood and to the porcellanites and hornstones of the 
Lilleshall and St. David's districts. Besides this there are 
chips of slate, with more or less conspicuous cleavage, and a 
variety of rocks, apparently of a somewhat schistose character, 
showing some recrystallisation as well as rearrangement of 
particles. These may be classed as slightly metamorphosed 
sediments. Many of the rocks consisting exclusively, or almost 
exclusively, of quartz are so little altered that they may be 
described as grits, and many other sedimentary rocks of some- 
what indeterminate character occur, including some with dis- 
tinct parallel structure and a good deal of finely disseminated 
black material, which is probably carbonaceous. These may 
perhaps be described as graphite schists. 
G 
