45 



chapter* it will U- keen by what steps he may most pro- 

 fitably a -Jim.- this kind of experience. 



nature and conduct of these preliminary eiu 



not only vary with the chant' c geology 



and physical features of the country, they differ accord- 

 ing to the extent to whuh the minify i* scaled and 

 populous, or trackless and unexplored ; according to the 

 existence or absence of maps of the region to be ex- 

 amined ; according to climate and other obvious miner 



jKxniliaritics as these, which greatly affect the first 



.1 traverses of a country, are apt to influence all 

 the subsequent more detailed work. 



As an illustration of the different conditions under 



i field-geology may be carried on, let me contrast 

 the work of the Geological Survey of Great Britain and 

 Ireland with that of the first cartographic examination of 

 an unexplored region like that of parts of the Western 

 Territories of the United States. In a long-settled and 

 populous country, such as Britain, there arc abundant 

 moans of communication by road, railway, or steamboat 

 between all or almost all districts. Villages and towns 

 are scattered so numerously over the land that we seldom 

 need be in any doubt as to obtaining good quarters. 



>fnny-post and electric telegraph accompany us even 

 into some of the most retired spots. Books, specimens, 

 and instruments can be sent to us at a few days' notice. 

 Of ever)' district in the British Islands we may procure 

 detailed Ordnance maps, by which to make our way over 

 the ground, and on which to place the results of our geo- 

 logical observations. Besides, the main features and 

 much of the detail of British geology are already known, 



