90 G, F. MATTHEW ON ILLUSTRATIONS OF 
universal prevalence of slaty cleavage. This in most cases has distorted and obscured the 
fossils of the finer beds of the formation and, indeed, obliterated them entirely in the 
greater part of the fine slates. It is only lately that I have been able fairly to appreciate 
the wholesale destruction of organic forms affected through this agency. 
During the extensive excavations that were made for the foundations of buildings in 
the principal streets of St. John, during the two years after the great fire of 1877, large 
quantities of fine black slate were removed, in which no trace of a fossil could be seen. 
But scattered at intervals through some of the bands of this slate there were hard compact 
masses of rock which, when broken, were found to be packed with fossils. The spherical 
and elliptical masses, which varied in size from about a yard in diameter to nodules of one 
inch across, had the appearance of imbedded boulders, but the fossils in them were always 
parallel to the stratification, and similar fossils were subsequently found in irregular beds 
and lenticular bands of hard rock. In the boulder-like masses there were numerous layers 
loaded with organic remains, which extended without diminution in the number of the 
fossils to the very edge of the block, where they suddenly disppeared, and not a trace of 
them could be found in the adjoining slate rock. The explanation of this curious fact 
seems to be that in the hard lump there was sufficient carbonate of lime to resist the 
molecular movement which produced slaty cleavage in the surrounding portion of the 
deposit, and thus to preserve the fossils from destruction. 
There are three great bands of black slates in the mass of the Saint John group on 
which the city is built, but which, owing to their softness, seldom appear at the surface, 
and it is highly probable that these bands originally abounded in organic remains. Such 
having been the destructive action of slaty cleavage on the Cambrian organisms of this 
district, the rarity in the finer sediments of fossils in a good state of preservation can be 
better understood. It is necessary to seek over large areas for such, and as a rule they have 
been found only near the base of the formation. 
Of all the genera of trilobites of the Saint John group Paradoxides appears to be that 
which has suffered most from the distortion due to the movement which produced slaty 
cleavage in the clay slates. Their tests were more flexible than those of the other genera, 
and their comparatively large size makes it more difficult to obtain specimens which will 
show the whole buckler (or even a considerable part of it) in a good state of preservation. 
The remains of this genus usually resemble crumpled fragments of grey or brown paper, 
laid irregularly one over the other, without any recognizable shape. When they are not 
too much crumpled and have their broadest surface parallel to the cleavage planes of the 
clay-slate they can generally be identified ; but the fossils are almost always at an angle with 
the cleavage, and are also more or less distorted diagonally to the axial line. Even when 
in the best state of preservation in the argillaceous matrix they are flattened by pressure 
and the tests cracked and mis-shapen. All these accidents of preservation, except the ver- 
tical flattening, have been allowed for in the drawings accompanying this article. Ina few 
cases specimens have been obtained which have been preserved from distortion by a large 
amount of carbonate of lime in the particular part of the layer in which they occurred, and 
in these original form of the organism has been more accurately preserved. 
The principal fossiliferous zone of the St. John group contains the exuviæ of many 
generations of trilobites, and probably those of several stages of growth of the same indivi- 
dual. Being a repository of the discarded clothing of many a living trilobite, as well as 
