384 Trilobites, Sc. in the lowest Shales of the Palzozoic Series. 
Let AB (PI. IV. fig. 8) denote the original position of the 
surface, a, b, 6 the lode; A!B! the new one to which the 
piece beyond AB, including the lode a’, 41, b!, has been ele- 
vated; and po the line of motion, which includes such an 
angle with the dip of the lode as to remove every part of a’, 
5', b' so far from the general position of the unmoved por- 
tion, that only the more prominent parts of both the segments 
shall be in contact when they are brought into direct opposi- 
tion. It is at these salient points only, as at b', b', that there 
is a simple intersection, whilst at all other parts of the down- 
ward course the heave is towards the left-hand. 
We have already seen (3.) that no motion parallel to the 
dip of the lode will satisfy the conditions before us; though 
oblique motion, within given limits, will afford an explanation. 
Yet as the extent of the heave depends on the amount of the 
motion, if that amount be unlimited, the mean distances of the 
heaves must progressively increase as they recede from a given 
point,—a state of things which is not found to prevail. 
It is obvious that if the line of motion always includes an 
angle with the same side of the lode, the heave at all levels 
must be in the same direction. If, however, the line of mo- 
tion pass through the undulations of the lode, leaving some of 
them on one side of it and some on the other, the heave, as 
previously shown (3.), will also of necessity be sometimes to- 
wards one hand and sometimes towards the opposite. 
[To be continued. ] 
LXVI. On the Occurrence of Trilobites and Agnosti in the 
lowest Shales of the Pulaozoic Series, on the Flanks of the 
Malvern Hills. By Joun Puiwures, Esq., FR.S. 
N the course of the Ordnance Geological Survey of Great 
Britain the occurrence of organic remains in black shales, 
very low in the series of the Silurian strata, has been found 
worthy of much attention by the Director and other members 
of the Survey, from the information they yield regarding the 
downward extension of the Salopian fossils into the lowest 
strata of Wales. On this account the fossils which have been 
collected from these shales in Pembrokeshire (Abereiddy Bay) 
and in Caermarthenshire (near Caermarthen, St. Clair’s, My- 
drim and Llandeilo,) will be found of more importance than 
from their limited number and generally imperfect preserva- 
tion could be inferred. 
Shales mineralogically undistinguishable from these occur 
in the Malvern Hills, nearly at the base of the whole Palzeo- 
zoic series, there exposed under circumstances of much in- 
