mZ 



NA TURE 



"3 



THURSDAY, DECEMBER 7, 1876 



THE YORKSHIRE LIAS 



'he Yorkshire Lias. By Ralph Tate and J. F. Blake. 

 (London: Van Voorst, 1876.) 



[T might at first sight seem a piece of presumption in 

 one whose palncontological attainments are of the 

 enderest, and who knows no more of the Yorkshire Lias 

 lan has been picked up during a few days ramble along 

 le coast, to attempt a criticism of a work conspicuous 

 ir elaborate pala:ontological research and rich in descrip- 

 ve detail of the most minute and local character. But 

 t forming an estimate of the work of a specialist the ab- 

 :nce of minute special knowledge is in many cases far 

 om being a disadvantage ; the specialist always runs 

 )me risk c^^ becoming engrossed with details^ of looking 

 jon them as the end and not as a means to something 

 gher, of being " unable to see the wood for the trees," 

 id ,as long as this risk exists, there is always a fair pros- 

 xt that the remarks of an outsider, however inferior he 

 ay be in special attainments to the man whose work he 

 reviewing, may add something in breadth of view, and 

 ;ay suggest questions that have been overlooked in the 

 :sk of collecting minute particulars. It is with this feel- 

 :g that we attempt to give an account of the work before 

 '""d to discuss some problems which its perusal has 

 ted to us ; and we make the attempt all the more 

 iKT.iy, because the authors have by no means in the 

 ultiplicity of their details lost sight of the broad ques- 

 l»ns which underlie and spring from them. 

 [The opening chapter on the " General Range of Liassic 

 J^ata on the Continent and British Isles" would have been 

 Itter for rather more copious references. The authors 

 oted may be well known to the mass of professional 

 |ologists, but if this book comes, as we feel sure it will, 

 the hands of workers of a more amateur class, 

 iikinly occupied with the geology of their own neigh- 

 urhood, but at the same time anxious to understand its 

 ation to that of corresponding districts abroad, many 

 its readers will certainly be glad of directions where to 

 d the papers of geologists not familiar to the world at 

 ge, and whose names they perhaps now meet with for 

 ; first time. This indifference to references is a grow- 

 i- nnd a very serious evil ; take, for instance, such a book 

 :ou's " Explication de la Carte Gdologique de la 

 '' to attempt to give in 200 pages a complete account 

 geology of the globe would be a hopeless task, 

 outhne no longer than this, abundantly furnished 

 ferences, would be a work whose value it would be 

 'X to overestimate ; unluckily M. Marcou has fallen 

 e prevalent carelessness in this respect, and for 

 cference he has given, ought to have supplied fifty. 

 ')ter II, gives an account of the literature of the 

 lire Lias; the abstracts of the various papers and 

 .^c on the subject are admirable for point and concise- 

 s, and the criticisms fair and just. In Chapter III. the 

 ge and general character of the Lias in Yorkshire are 

 Ciirly sketched out. 



The fourth chapter lands us in one of those disputes, 

 u Avoidable possibly in the present state of geological 

 clature, which have far too much the look of fight- 



ing about mere words to be altogether satisfactory. The 

 point at issue is, where should the line be drawn between 

 the Lias and the Inferior Oolite? In some cases the 

 demarcation between the two formations is both litho- 

 logically and palasontologically so sharp as to leave no 

 room for hesitation ; but some sections show a group of 

 beds in which fossils that occur in the Upper Lias are 

 found side by side with others generally looked upon as 

 characteristic of the Inferior Oolite. Here, then, was a 

 fine battle-ground for the systematists, and here, accord- 

 ingly, as in other analogous cases, much good ink and 

 paper has been — shall we dare to say — wasted in dis- 

 cussing whether the problematical strata ought to be 

 called Liassic or Oolitic. Dr. Wright maintains the first 

 view, and the authors of the work before us lean to the 

 second, the question being argued by both disputants on 

 purely palreontological grounds ; it turns partly upon the 

 correct naming of certain Ammonites, hard to discrimi- 

 nate from one another, and possibly so closely allied that 

 they ought to be looked upon as varieties rather than dis- 

 tinct species ; it involves many points on which there is 

 great difference of opinion, such as whether we ought to 

 look mainly to the Cephalopoda or to the Conchifera in 

 determining the relationship of the group ; and after 

 carefully considering what has be^n said on both sides, it 

 certainly seems that it is one of those cases where the 

 impartial bystander would find it so hard to make up his 

 mind that he would be sorely tempted to resort to the un- 

 scientific method of " tossing up " to help him to a decision. 

 Fortunately there is a better way out of the difiiculty ; 

 we are not tied down, as the manner in which the ques- 

 tion has been handled would seem to imply, to a single 

 alternative. It is an easy thing to say that there shall be 

 a Liassic group and an Oolitic group, and that of the 

 rocks about the junction, what won't go into one shall be 

 forced into the other, and by adopting this principle very 

 neat tables of strata may be constructed. But if, as the 

 group under consideration proves was the case, there was 

 not a clean sweep of the Liassic forms of life before any 

 Oolitic forms came in, but that to a certain extent the re- 

 placement was gradual, then wherever the record of the 

 change in the least degree approaches completeness, beds 

 will occur which contain a mixture of Liassic and Oolitic 

 species, and consequently cannot be placed consistently 

 under either of these heads. It is unfortunate for the 

 symmetry of our classification that it is so, but being so, 

 we must bear the evil as best we may. Perhaps the 

 best way is to let each man call the beds in dispute Lias 

 or Oolite as his fancy prompts him, but to be careful to 

 bear in mind that the meaning they carry with them is 

 this — that, when they occur, we have been lucky enough 

 to have preserved a record, which at other spots either 

 never existed or has been destroyed, of the rate at which 

 changes in life that took place between two indistinctly 

 outlined periods of the earth's history were brought 

 about. 



It would not, of course, be fair to blame Messrs. Tate 

 and Blake, when they are writing a monograph on the Lias, 

 for explaining what they mean by that term ; but it would 

 possibly have been more philosophical if they had looked 

 upon their upper boundary as purely conventional, and 

 noticed the beds above that line as of interest because 

 they show a gradual passage from the life of the period 



