xii PREFACE. 
the Table-Case and column of Drawers (as Gh. 1); the second column giving illustrative figures 
of various genera, and also references to M*Coy’s Synopsis; the third giving the names 
adopted by Mr Salter, with references to one or more works in which they have been 
described or figured, with the addition of useful short notes on the species; the fourth 
column giving the localities from which the specimens have been obtained. 
I should ill discharge my duty in writing this Preface did I not gratefully notice the 
elaborate Index which Prof. Morris has added to the Catalogue. It is a graceful finish to 
the work, and makes the Catalogue fit for ready consultation, which is a matter of the 
first importance. This Index has been a work of such labour that I should not have ventured 
to ask the Professor to undertake it; but this thought makes me the more grateful to him for 
having contributed it so kindly and spontaneously. With like expressions of grateful 
goodwill I must also mention the Tables, in which is given an account of the whole range 
of formations within which each genus has been found; so that an eye-glance at these Tables 
will put a Paleontologist in possession of the leading facts of the distribution of the organic 
types in the successive groups of Strata, as they are enumerated in the Catalogue: not in 
any hypothetical order, but in that in which they are recorded in Nature’s Book. These 
Tables are a work of great knowledge and of patient skill; and went far beyond the task 
of revision intended by the University. 
The stratigraphical System of nomenclature adopted in this Catalogue is essentially 
the same with that of Prof. M°Coys Synopsis. It is based upon an actual survey, first 
made by myself, whereby I approximately determined in N. Wales the order of the older 
deposits of the whole region, and the natural groups of strata into which they might be 
separated. 
This might be called a great but rude problem of solid geometry, to be first solved 
by an elaborate examination of physical evidence, and without reference to the organic 
remains in the successive groups. But these groups being once established, on the basis of 
true observation, we may then proceed to obtain the first chapters of a true history of 
the succession of organic types, as the tale is told in the successive strata whence they 
have been derived. And when we have once obtained in any extensive section a true 
succession of organic types, we may then, as Nature is true to her own workmanship, 
advance a step farther, and use that succession to help us in making out the order of 
the Physical groups in cases where they have been imperfectly or obscurely elaborated. 
Thus we have two great principles of arrangement; first by the actual and laborious 
observation of the successive physical groups; secondly, by the order of the organic types which 
have been already established by a reference to the types of some well-known natural section. 
