.mm^i Prof. Sedgwick on the May Hill Sandstone. 301 



9. It is evident that the unsymmetrical distribution of land 

 and sea, which gives rise to the abnormal variations in the forms 

 of the isothermal lines, is at the same time the principal cause of 

 the movements of the atmosphere. Thus the monsoon is but a 

 modification of the trade wind, of which the cause is to be sought 

 in part beyond the tropic. The region of great thermic expan- 

 sion of the air in summer in the interior of the continent of the 

 Old World presents all the characteristic marks of the region of 

 calms, being a centre towards which all adjacent masses of air 

 are drawn. Hence there is no complete sub-tropical zone, in the 

 sense of a zone encompassing the globe. The region over which 

 the heated air ascends does not therefore move up and down, or 

 north and south, parallel with the sun's change of declination, 

 but has rather a kind of oscillatory movement, in which the 

 West Indies represent the fixed point, and the greatest ampli- 

 tude of oscillation is on the side of India. The northern excur- 

 sion is much greater in the northern hemisphere than is the 

 southern excursion on the side of the southern hemisphere. 

 The European atmospheric relations, especially in summer, are 

 therefore essentially of a secondary nature ; and we must regard 

 the little alteration in the atmospheric pressure in the course of 

 the year in Europe as a secondary result, of which the explana- 

 tion would not have been possible without the observations from 

 Asia and Australia. 



Berlin, January 5, 1853. 



XL. On the May Hill Sandstone, and the Paleozoic 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, 



THE following paper was drawn up for the Geological Society 

 of London during last October, in the hope of its being 

 read at their first Meeting after the summer recess. I was, 

 however, too late in my application ; and in consequence of a 

 long protracted illness, I was never able to attend a single meet- 

 ing of the Society during the past winter or during the spring 

 of this year. The paper was consequently postponed, and at 

 length read, in my absence, at one of the concluding spring 

 Meetings of the Geological Society. The Council are ready to 

 print the paper — suppressing the discussions on classification 

 and nomenclature — in their Quarterly Journal. I believe that 

 any such suppression would destroy the value of the paper ; and 

 I oiFer it to you as it was originally drawn up, with the following 

 exceptions. One of the diagrams (fig. 4) has been corrected — 



