and of Trap in different Parts of Scotland. 241 



In countries of this structure also, as in the granitic districts 

 of Aberdeenshire, a depth of alluvia sufficient to conceal ef- 

 fectually the subjacent rocks, is a perpetual source of obscu- 

 rity and labour. Here, indeed, it commonly arises from a dif- 

 ferent cause, the alluvial covering being the produce of the de- 

 composed trap itself, and proceeding from that cause which 

 has produced the discontinuity of the larger masses, and insu- 

 lated the detached spots and summits which abound in dis- 

 tricts of this nature. 



To quote examples of the fact now noticed, would be to 

 enumerate nearly all those districts in Scotland where trap oc- 

 curs. I shall satisfy myself with stating, in the most general 

 manner, that they may be found in the whole central district 

 of Scotland, which is included between the Highland moun- 

 tain boundary and the schist of the south. Whoever may 

 wish to make a map of this tract, as of many others in Scot- 

 land, may be assured that he will only succeed by examining 

 nearly every square yard ; and that, without this attention, 

 he will only produce that which will be as useless for its in- 

 tended purposes as discreditable to himself. 



I need not prolong this subject, and shall be satisfied if these 

 hints, the fruit of hard experience, shall be of use to those 

 who may intend to labour in this department of geology, or to 

 those who expect to profit by their labours. 



Art. XI. — Remarks on the Influence of the Winds on the Ba- 

 rometer. Communicated by the Author. 



About the beginning of the last century, Mr Hawskbee pro- 

 posed the following experiment to explain the descent of the 

 barometer during a storm. " Having connected the cisterns 

 of two barometers by a horizontal pipe of three feet, he insert- 

 ed in the side of one of them a pipe opening outwards, and 

 connected the other side with a large receiver, into which three 

 or four charges of atmosphere had been compressed ; on open- 

 ing the cock the air rushed with vehemence over the mercury 

 in the cistern and effected its escape, while both columns fell 

 simultaneously about two inches, and rose again as the force 



VOL. II. NO. II. APRIL 1 825. K 



