xii PREFACE. 
species or to house work, but if he must dredge he will be 
wise to select a convenient spot on the shore, such as where 
there are flat clean rocks with deep rockpools, and there 
take up his stance, sending the boatmen seaward to the bank 
which is to be examined, spreading the material obtained on 
one of the rocks, washing it in the pools, and examining and 
sorting it at leisure, whilst the boatmen return to sea for a 
farther supply. 
These remarks are, of course, only for such as are obliged, 
like myself, to hire small sail or rowing boats, and to make 
the most of a short holiday by gathering as much material 
as possible in the shortest space of time. Those on the other 
hand, who can command the use of large yachts, especially 
steam yachts, and whose time is not limited by other affairs, 
are quite differently situated, being more or less independent 
of the elements as well as being able to choose their work- 
ing days; the discomfort of dredging in stormy weather 
with asmall skiff is very great, and to such as do not possess 
strong stomachs, impossible. 
In concluding this already too long preface I have only 
to express my indebtedness to Mr. David Robertson, of this 
city, for the opportunity afforded me of examining his 
unrivalled collection of Clyde shells, numerous references to 
which will be found in the following pages. To Mr. John 
Gray my thanks are specially due for his care in seeing this 
booklet through the press. 
20 HuntLy GarpeEns, December, 1877. 
