2S14,J emitted from the Lungs in Respiration. 33? 



induced me to submit these observations to the world. Hence I 

 content myself with little more than stating matters as I have found 

 tliem, still waving all speculations, however interesting they may 

 be, till the matter has been thoroughly investigated, or at least 

 much better examined into, either by myself or others. 



Article IV. 



A GeognoUical Sketch of the Counties of Northumberland, Durham, 

 and Part of Cumberland. By Thomas Thomson, M.D. F.R.S. 

 With a Map.* 



The counties of Northumberland and Durham (including a 

 portion of Cumberland and of Yorkshire) in a mineralogical point 

 of view, are perhaps the most important in Great Britain ; since 

 they supply London, and almost all the east and south coast of the 

 island, with coals; and since the quantity of lead which they 

 annually yield is probably not much inferior to what is furnished by 

 all the rest of Europe. These counties have been mined in all 

 directions for so long a series of years, that we are perhaps as well 

 acquainted with their internal structure as with the nature of the 

 surface. Most of the beds extend with great regularity for a consi- 

 derable space. They have been recognized by the miners as the 

 same, and have been distinguished by the same names at places 

 situated at a considerable distance from each other. 



The facts from which I have been c abled to draw up the fol- 

 lowing sketch were ascertained 'jy me during a tour of a few weeks 

 duration, which I made )«st August, on purpose to form some 

 notion of the nature of these important counties. 1 traversed both 

 Northumberland and Durham in various directions ; and partly 

 from my own observations, partly from the information which I 

 obtained from the different mining agents, I was enabled to form 

 what I conceive to be a pretty accurate idea of their structure. To 

 assist the reader as much as possible in following the description 

 which I mean to give, I shall insert an outline map of the counties, 

 On which 1 have coloured the different formations in order to distin- 

 guish them from each other : but I must warn the reader not to 

 suppose that the boundaries of these different formations have been 

 narked out with precision. In some few spots 1 succeeded myself 

 in determining the. termination of a formation with tolerable exact- 

 In many cases I have been guided by the information of the 

 mining agents; but 1 have no duubt that 1 have committed occa- 

 sional mistakes, especially respecting the north-west part of 

 Northumberland, which I did not vi>it ; nor did 1 ascertain the 

 structure of the Cheviot.-, to what class of rocks they belong, or 



* Tin- M.ip v. ill be giv-i, in tilt next iiiimtiur. 



Vol. IV. ft V. V 



