42 TRANSACTIONS OF SECTION C. 
The former genus has a large number of species, many of which are to 
be found in the Beekmantown limestone of Newfoundland and Eastern North 
America. Only one of the species (Maclurea Peachi) is peculiar to Durness. 
Several species of Ophileta are found, some of which likewise occur in the Beek- 
mantown limestone. Euomphalus has also been recorded, while several forms — 
belonging to the nearly allied family of the Turbinide, and placed in Lind- 
strom’s genus Oriostoma, are also met with in the Beekmantown limestone. 
Murchisonids and Pleurotomarids number twenty-seven species and show a 
very wide range of variation. The chief subgenera of the former are Hormo- 
toma and Hetomaria, many species of which occur with remarkable variations. 
All the types of variation found in Durness are to be found in North America, 
and several of the species are common to both regions. The pleurotomarids 
vary in a similar manner, the chief genera being Raphistoma and Luconia, and 
a form resembling Hormotoma, only with a shorter spire. Species belonging 
to each of these subgenera are likewise common to both areas, while some are 
only known from the North-West Highlands. 
The cephalopods are of equal interest. They are also of primitive type 
and, at the same time, show a wide range in form. The prominent feature in 
the straighter specimens is the great width of the laterally placed siphuncle, 
which is generally furnished with endocones and organic deposits. The genus 
Piloceras is the most characteristic type and shows this peculiar feature best. 
It has only been recorded from Scotland, Newfoundland, Canada, and the 
eastern States of North America. ‘The following additional genera are repre- 
sented—viz., Hndoceras, chiefly by siphuncles in great variety; Actinoceras, 
Cyrtoceras, and, doubtfully, Orthoceras. Several forms have been attributed to 
Orthoceras which, on re-examination, have been found to be the siphuncles of 
other genera, resembling American types described by Hall and Whitfield. 
The whorled nautiloids provisionally classed with the genus Z’rocholites of 
Conrad are represented by several distinct forms as yet unnamed. 
The trilobites are of rare occurrence in these two groups of dolomite and 
limestone. They are fragmentary and poorly preserved. This is doubtless one 
of the disappointing features connected with this remarkable assemblage of 
organic remains, for the presence of a zonal form would have helped to define 
the horizon of these beds. Only one species, Bathyurus Nero (Billings) has been 
identified, which also occurs in the Beekmantown limestone of Newfoundland. 
The other trilobite remains, though poorly preserved, leave a Cambrian facies 
characteristic of North America. 
In connection with this fauna certain features have been observed which 
throw some light on the absence of calcareous organisms from thick zones of 
the Durness dolomite and limestone. In my detailed description of the 
paleontology of the Cambrian rocks of the North-West Highlands in the 
Geological Survey Memoir I stated that ‘in most cases the septa and walls of 
chambered shells have been wholly or in part dissolved away, so as to leave 
only the more massive structures of the siphuncles, and worm castings are often 
found within the chambers where the septa have been preserved. These 
features seem to indicate that the accumulation of the calcareous mud in which 
the fossils were embedded was so slow that there was time for the solution of 
part of an organism before the whole of it was covered up.” There is good 
reason to believe that many organisms wholly disappeared by this process, so 
that it is reasonable to conclude that the fossils obtained from the Durness 
dolomites cannot be regarded as furnishing a complete life-history of the forms 
that originally existed in that sequence of deposits. Attention has already been 
called to the fact that beneath the two subdivisions now under consideration 
there are groups of dolomite and limestone which so far have yielded no organic 
remains beyond worm castings. And even in the important Croisaphuill group, 
with its fossiliferous zones, there are thick groups of dolomite which have fur- 
nished no calcareous organic remains. Obviously the paleontological record in this 
instance is glaringly incomplete, for we have no reason to suppose that the life 
of the time flourished in some of the calcareous zones and not in others. 
The highest subdivision of the Durness limestone, measuring about 150 feet 
® ‘Geological Structure of the North-West Highlands,’ Geol. Sur. Mem., 
1907, p. 380. 
