150 OBSERVATIONS ON THE 
and we find that all the characters we observe in our own 
District have their counterpart in the others. The horizons 
which are most variable here, have the greatest number of 
different developments elsewhere, and the somewhat isolated 
fossiliferous zones, though not to be all exactly found in any 
one of the other sections quoted, can be identified 7% one or other 
of them, so that a fair probability is presented that we have a 
true sequence. 
In our District, as in the north of England, the beds which 
conformably succeed the Silurian are nowhere represented, nor 
are there any beds lithologically or palzontologically like the 
Kirkby Moor Flags of the north, or the Tilestones of the south. 
Indeed, it is very doubtful, whether we have left z# sztu any 
equivalent of the Benson Knot beds, or of the Downton Sand- 
stone But here comes in the difficulty, that almost all the 
species, which by the concurrence of a very large number of 
individuals, give a distinctive character to the massive sandstones 
of the Upper Ludlow, do occur sporadically through both 
Coniston and Denbigh Grit Series; and in one case in the 
north of England, where suitable conditions prevailed, are found 
in the very same association low down in the Coniston Grit 
(see p. 147), so that this anticipation of Ludlow, or antitype 
of a colony, should teach us caution in inferring that we must 
be high up in the series because of the appearance of a group 
of the forms which are generally individually more numerous in 
the Upper Ludlow. 
Below these sandstones, however, our review of surrounding 
areas leads us to look for very thick beds of shale with a 
tendency to become flaggy. Shales represent the finer sediment 
which has been carried far away from its source, and has been 
allowed to settle down out of reach of constantly shifting 
currents, generally in deeper water and further from land We 
may expect, therefore, to find that the great shales are of wider 
extent and of greater constancy of occurrence at the same 
horizon, than any of the basement deposits, or even than the 
grits and sandstones which occur higher up in the series. But 
where the depression has ceased, or at any rate no longer keeps 
pace with the denudation of the nearest land, and the consequent 
deposition in the adjoining sea, there the whole basin must be 
silted up, and, shallow water again prevailing, currents will carry 
coarser sediment over the area. Thus, we may expect to find 
sandy sediment in the highest beds which creep out from below 
the unconformable Mountain Limestone, with its basement 
conglomerate, near Llysfaen, and other places along the North 
Wales borders. 
SALTER was of opinion that in the Llansannan Shales we had 
beds higher in the series than the main-mass of the Denbigh 
Grits. I am not in a position to confirm this view, but have 
great suspicions that the Llansannan Shale passes under the 
