14 



Relations of Geology to Agriculture 



of the rocks themselves. If thej consist of limestone, the rains 

 may wash down the finer particles from many places ; but 

 wherever soil remains it will still retain nearly the same com- 

 position as at first, and will be little impaired in fertility by the 

 action of the rains. Hence the fine sweet herbage which clothes 

 our limestone-hills, and makes them so grateful to the pasturing 

 flocks. Or if hills or table-lands of red marl* form the higher 

 country, portions may be washed down without materially affect- 

 ing the quality of what remains. Let a fresh portion of the rock 

 crumble, and things are again as they were before. A new soil 

 is produced, equally fertile with that which has been washed 

 away, and thus the fertility natural to the rock will be perma- 

 nently maintained. 



It is different, however, in the case of sandstone rocks, such as 

 those of the coal-fields of New Brunswick. When such rocks 

 crumble they form soils more or less sandy, according to the pro- 

 portion of fine clay which has been originally contained in the 

 materials from which the rock was formed. Now, the action of 

 heavy rains upon such a soil is not to carry it away bodily, as in 

 the case of the limestone or of the fine red marl, but to wash out 

 the fine clayey particles, and carry them down to lower levels. 

 Thus on the uplands the sandy soils become every day more 

 sandy and of less value, while, in the direction of the drainage, 

 they become, on the other hand, constantly more tenacious and 

 productive. 



Thus the amount of influence exercised by physical drainage 

 is itself limited, and determined by the chemical composition of 

 the rocks of which the country consists. 



5th. That the passage of rivers or of sea-arms across a poor 

 country, after it has previously traversed a richer geological 

 region, is sure, to a greater or less extent, to modify — to increase, 

 in fact, the value of the surface in the line of its course. This 

 is seen, as I have pointed out, on the St. John river, and at the 

 head of the Bay of Fundy, and is confirmed by observations 

 made by myself and others in nearlj all parts of the world. 



6th. That partial elevations of the land at successive periods 

 will aid other physical causes in establishing such differences, 

 often, as in New Brunswick, covering with more fertile land the 

 surface which has been most recently raised from beneath the 

 waters of seas or lakes. It is conceivable, however, that in other 

 conditions the very converse may take place. 



These practical results are drawn directly from the map before us. 

 Of course they do not indicate or exhaust all the causes by which 

 modifications are introduced into the agricultural indications of 



* Such as is represented in our sections by (3). 



