DORSET-SOMERSET DISTRICT. 35 



Comparison of the Dorsetshire and Yorkshire Coasts. 



There is, perhaps, no portion of the Inferior Oolite throughout England which 

 is so well illustrated as the Parkinsoni- zone of Burton Bradstock Cliff, even down 

 to very minute details, and it is, of course, all the better for not being inflated 

 with too much sedimentary matter. As this is the first glimpse of the Inferior 

 Oolite in England, for one coming from the south it might perhaps produce an 

 exaggerated notion of the importance of the Parkinsoni-zone. 



One cannot help reflecting on the marvellous contrast presented by the section 

 of the Inferior Oolite on the Yorkshire coast. Setting aside the enormous 

 difference of physical development, we have in the Nerinaa-bed of the Yorkshire 

 Dogger a fine development of the MurchisoncB-zone, and this is indeed the only bed 

 of the Inferior Oolite which can be regarded as rich in Gasteropoda in that county. 

 But owing to the difference of facies even the Murchisona-hed of Burton Bradstock 

 Cliff has not much more resemblance to the Yorkshire Dogger than the beds of 

 the Parkinsoni-zone have. It has many Ammonites and no Nerinceas, whereas the 

 Yorkshire Dogger has many Nerinaeas and hardly any Ammonites. If we carry 

 the comparison a step higher we find the Cephalopoda of the Humphriesianus- or 

 coronaten-zone abundant in certain portions of the Scarborough Limestone, 

 whereas in Burton Bradstock Cliff this zone is aborted, or so overshadowed by the 

 lower part of the Parkinsoni-zone as to produce no impression. Again, on the 

 Yorkshire coast there is no palseontological representative of the Parkinsoni-zone, 

 so that in all respects the contrast is most complete. 



In every respect, therefore, the marine beds of the Inferior Oolite on the 

 Yorkshire Coast differ surprisingly- from those of Dorsetshire. Yet despite this 

 difference the relative position of the life zones is always the same so far as the 

 Cephalopoda afford the means for comparison. It remains to be seen how far this 

 holds good for the Gasteropoda. The contrast between the species of Gasteropoda 

 in our Lower and Upper Divisions is exceedingly marked throughout the Dorset 

 District, where the abundance and excellent preservation of the Gasteropoda admit 

 of the fact being proved to demonstration. Possibly the difference may be shown 

 to a certain extent in the Cotteswold District (No. 2), but less clearly, I think, in 

 the Yorkshire District (No. 4). 



Reverting once more to the Parkinsoni-zone in Burton Bradstock Cliff, it seems 

 to me that the Cotteswold divisions of the Ragstone are to a certain extent pre- 

 figured in this exposure. Making due allowance for geographical distance and 

 difference of facies, I think that P : corresponds in the main to the Upper Trigonia 

 Grit, though here fortunately the matrix is quite of a different character, hence 

 lithologically there is no resemblance. Moreover, Bhipichonella spinosa does not 



