sEPT. 1899] THE SILURIAN ROCKS OF BRITAIN 207 
as a matter of vastly greater importance than the history of the fossils occurring 
in the strata which that dyke happens to cross. Whether the dyke consisted 
of basalt or of “‘melaphyre,” or whether it should be called a dolerite or a 
“diabase,” has in Scotland only too often been considered a question of far 
greater importance than whether the graptolites which occur in the strata 
traversed by that dyke indicate that the rocks are of Arenig age, or whether 
they date from Wenlock times, or, again, whether they represent any period of 
intermediate age. We cannot all be specialists, it is true ; but, clearly, every 
modern geologist should be familiar with at least the zonal fossils of the rocks 
amongst which he is at work. One would also think that his work would 
prove of much greater interest to him if he knew something of the biological 
relationships of the organic remains with which he is likely to meet. As things 
stand at present, it may be confidently stated that, taking the whole of Scot- 
land, the number of those who are really working at fossils of any kind may be 
counted on one hand—one of the authors of the present work being one of 
them. And even the number of those who are systematically making collec- 
tions of fossils probably does not exceed a score. The case, of course, is very 
different south of the Border, where nearly every geologist takes a more or less 
keen interest in Palaeontology. 
That these defects will soon be made good no one who carefully studies the 
most admirable historical introduction given in one of the earlier chapters of the 
book under notice can for a moment doubt. The whole of that history leads up 
to a triumphant vindication of the claims of Palaeontology to occupy a foremost 
place in the studies of all geological students in the future, not only on account 
of the ight which that science throws upon the evolution of existing forms of life, 
but also on account of the invaluable aid it affords in unravelling the complicated 
structure of districts like that of Girvan, or of the Valentians or Southern 
Uplands of Scotland. Had it not been that Professor Lapworth brought to 
bear upon the rocks of these districts a combination of skill in field work with 
an extensive knowledge of Palaeontology, we should probably stil] have been 
no wiser regarding the true history of the rocks in question than we were thirty 
years ago. 
On taking up the work whose contents have suggested these remarks, the 
reader will do well to give a full consideration to the section of the book 
referred to. He will find in it evidence of a strongly-marked desire on the 
part of the authors to deal in a generous spirit with the work of all previous 
observers, and he will further see how each man has added something of his 
own to our knowledge of these difficult rocks, and how that intellectual giant 
amongst geologists, Professor Lapworth, largely by working out the zonal 
distribution of the Graptolites, has enabled us, in the end, to gain a clear view 
of the true succession of the Scottish Ordovician and Silurian Rocks. By the 
light thus presented, Messrs. Peach and Horne, with Mr. Macconochie, have 
laboriously worked over the whole area where these rocks occur, and, bringing 
to bear upon them the results of wide experience, they have completed the 
survey of the whole area of which this book treats. It is from the vast mass of 
material collected in the course of this work that Mr. Horne has completed the 
present Memoir. No one who takes the trouble to read any section of it 
can fail to see that, in all respects, it forms a perfect model of what such a book 
should be. It may truly be said to present all that can be known at present 
regarding the geology of the group of rocks to which it specially refers, and 
Sir Archibald Geikie is to be congratulated on the production by his staff 
of a Survey Memoir in which the work of eminent specialists like Mr. Teall, 
Professor Lapworth, Dr. Traquair, as well as Professor Laurie and Mrs. Robert 
Gray, has been skilfully incorporated with the vast mass of information collected 
by the above-named members of the field staff of the Survey. 
It may be well to mention here that the various geological maps, rock 
specimens, and most of the fossils, referred to in the Memoir, are exhibited in 
