VARIED ASPECTS OF SLATE. 
35 
loosely informed on the matter is termed clay-slate, 
and which I have above recognised in a general way 
as being fossiliferous, must receive this appellation. 
From what I have just stated, it might be gathered 
that thd^interruptions to the courses of the different 
varieties of slate are not sudden, but rather the re¬ 
verse. This circumstance indeed, is remarkable 
amongst the features of this rock considered as a 
whole. Mica-slate, clay-slate, (used in a limited 
sense) roofing-slate, grey-dunstone and greywacke 
slate, are observed to pass gradually into one another, 
and to reciprocate each other’s qualities. Again, 
greywacke-slate, flinty-slate and greywacke gradu¬ 
ate into one another. Roofing-slate is found spa¬ 
ringly, and in small patches. It obviously passes 
into the general mass of clay-slate, of which, not¬ 
withstanding its containing organic remains, I have 
above surmised that it may in propriety be ranked 
a part. The general body of clay-slate assumes a 
great variety of aspects, which are manifestly gradu¬ 
ated, sometimes approximating the typical roofing 
slate and sometimes degenerating into a loose, brown 
nibble, or becoming indurated or closely impacted 
constituting “grey dunstone;”notunfrequently also 
running into decided greywacke, either in small 
patches or even in extensive beds. Altogether, 
these last named rocks form the generality of our 
hills, which are round-backed. In situations where 
the slate is in tolerable sized fragments, fossils are 
found in plenty. Although I have mentioned certain 
kinckvpf slate as being fossiliferous, I believe that 
no fixed rule can be laid down on this subject, for 
the sam£ kind of slate will in one place exhibit these 
remains, and in another be destitute of them. 
Greywacke-slate is most constant in this respect. 
The rubbly and loose kinds of clay-slate, and the 
best kinds of roofing-slate, but seldom contain them. 
The generality of our slate, that namely, to which I 
