Some idea of the extent of the work which the author mapped out for himself in this book may be formed from the opening words of the Preface:
"A sarcastic writer lately advised authors treating on Irish subjects not to omit commencing their essays from the starting point of the Biblical Deluge, so that no fact, direct or collateral, in the matter under consideration might escape notice. Critics do not, as a rule, confine themselves between too narrow limits, but the above recommendation, though good in its way, does not give a wide enough field to work on, at least when Ancient Erin itself is in question. The liberty, therefore, is taken of ignoring the well-meant advice, of exceeding the prescribed limit, and the subject is opened somewhere in the early Glacial, or perhaps in the Tertiary period. The writer has, in fact, placed himself in the unenviable position of the advocate who, opening his speech with the sentence, 'Before the birth of the world, ' was cut short by the judge, who exclaimed: 'Do you not think that we might pass on to the Deluge?' "
The book is almost bewildering in the abundant material collected within two volumes. Some idea of the wide research which the author brought to the work may be formed from a glance at the bibliography at the end of the second volume which shows nine hundred and eight sources of information. The result is a wonderful collection of legends and stories, traditions and superstitions, running through the centuries with all the variations which time works in such fields. The curious reader may find here the origin of many strange customs and beliefs which have persevered to the present day.
In a work of this kind it is hard to preserve exact order, and the author tells us that his object was to get the many sides of a great subject before the general reading public, with the hope that some great writer will do for Irish archaeology what a Prescott and a Motley have done for history at large.
Many readers of the book, while they admire the indefatigable zeal of the author in gathering his materials together, will not agree with him in his deductions. Here is the keynote to a line of reasoning running all through the work: "Christianity is generally supposed to have annihilated heathenism in Ireland. In reality it merely smoothed over and swallowed its victim, and the contour of its prey, as in the case of the boa-constrictor, can be distinctly traced under the glistening colors of its beautiful skin. Paganism still exists, it is merely inside instead of outside."
-"The American Catholic Quarterly Review," Volume 28