various deposits can only be effected by a thorough investigation of their 
fossil contents. 
This is tlie’dask which Messrs. Nicholson and Etheridge have set themselves 
to fulfil, with the aid of a grant from the Royal Society. A considerable 
number of fossils had already been described from the Girvan deposits ; but, 
as a matter of course, in many cases the descriptions were unaccompanied by 
those precise stratigraphical details which alone could render them available 
for the interpretation of the beds ; and the authors were under the greatest 
obligations to Mrs. Gray, of Edinburgh, whose collections, amassed with the 
greatest care, were placed freely at their disposal. Accordingly their mono- 
graph of the fossils, of which the first fasciculus is now before us, is stated 
on its titlepage to bear special reference to the fossils contained in the 
“ Gray collection.” 
In this first fasciculus the authors describe the Rhizopoda, corals, and 
trilobites which have been collected from the Silurians of Girvan, and which, 
especially in the first two groups, include many exceedingly interesting 
forms, a great number of them representing species and even genera pre- 
viously unrecognised. The study of the corals leads the authors to certain 
general views as to the age of the deposits from which they are derived, and 
they distinguish the following local divisions : — 
1. The Craighead limestone, which contains a peculiar set of corals, indi- 
cating Lower Silurian age, and having an American facies, leading the 
authors to regard it as corresponding to the upper part of the Trenton 
Limestone, or the base of the Cincinnati and Hudson River formations of 
North America. 
2. The Mulloch Hill beds, containing Heliolites interstinctus and other 
fossils, indicating an age equivalent to that of the Upper Llandovery. 
3. The Penkill beds, with the above Heliolites , Halysites catenularius and 
a species of Ccdostylis , indicating a position in the lower parts of the Upper 
Silurian series (WenlockP). 
4. The Shalloch Mill beds, containing Favosites gothlandicus and 
Alveolites Labechei, ummistakably indicating Upper Silurian age. 
5. The Balcletchie beds, coarse, fossiliferous volcanic ashes, with very 
few corals, which the authors suppose to be nearly of the same age as the 
first mentioned series. 
It will be seen that although the materials for forming a notion of the 
stratigraphical relationship of these deposits are still scanty, certain definite 
points are already laid down, and in all probability the authors will be able, 
before concluding their labours, to arrive at satisfactory results. Under any 
circumstances, however, even if the extant material be insufficient for this 
purpose, they will leave to future investigators of this interesting district a 
great mass of most valuable material admirably worked up. It is, in fact, 
impossible to speak too highly of the conscientious and careful manner in 
which Messrs. Nicholson and Etheridge have performed their self-imposed 
task ; but their style of work is so well known to all palaeontologists, that 
we may spare ourselves the trouble of seeking for complimentary phrases in 
which to express cur appreciation of their present effort. The work is 
illustrated with nine plates of fossils, lithographed by Mr. Berjeau, partly 
from nature, partly from the drawings of Dr. Nicholson, and of these we 
