472 Prof. Sedgwick on the May Hill Sandstone^ 



west side he can tell, as he may generally infer, when a change of 

 wind takes place against the sun and the wind blows strong, that 

 the ship is in a cyclone. It is not difficult to give for both hemi- 

 spheres independent rules for Judging on which side of the 

 cyclone a ship is. I have given such rules in detail in special 

 memoirs, but I should make this letter too long if I were to 

 enter on them, and they are also somewhat foreign to its imme- 

 diate purpose. 



Believe me, dear Sir, 



Sincerely yours, 



H. W. Dove. 

 To Captain Washington, R.N., F.R.S., 

 Admiralty, 



LX. On the May Hill Sandstone, and the Palaozoic System of 

 England. By the Rev. Prof. Adam Sedgwick, F.R.S., F.G.S, 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



HEREWITH I send what might, without impropriety, be 

 called a continuation of the paper you have done me the 

 favour to publish in the October and November Numbers of your 

 Journal. The task undertaken by Professor M'Coy and myself 

 in 1853 was left incomplete; but we have this autumn taken it 

 up where it had been abandoned, and completed our examination 

 of various critical sections, at the junction of the Cambrian and 

 Silurian rocks, which we had not been able to visit during the 

 preceding year. Is there in South Wales any " Middle Silurian '* 

 group in which the characteristic Silurian and Cambrian types 

 are so mixed and confounded as to be inseparable ? In North 

 Wales and Siluria we found no such group. Wherever it had 

 been erroneously laid down as one group we found it separable 

 into two distinct stages — the upper of which contained a cha- 

 racteristic Silurian group of fossils — and the lower, an equally 

 characteristic Cambrian group. But I was informed that near 

 Builth, in some of the eastern hills of Radnorshire, and in several 

 sections near Llandovery, the Government Surveyors had found 

 the veiy mixture of older and newer types which we had sought 

 for in vain during our short excursions in 1852 and 1853. To the 

 places thus indicated (taking the Presteign sections on our way) 

 we first bent our steps, and the results of our examination will 

 be given in the early part of this communication. They are in 

 perfect agreement with what we had before seen in North Wales 

 and Siluria. There is, we believe, no " Middle Silurian group '' 

 like that laid down in the Government Survey — there is no con- 

 fusion of organic types — the May Hill group (though in a dege- 

 nerate and disconnected form) does exist, in the county here 



