36 GEOLOGICAL :memoirs. 



The littoral region is the most fruitful in grain and the most densely 

 peopled, both from its fertility and on account of its maritime com- 

 merce and fisheries ; then follows the central zone, possessing the 

 largest extent of meadows, and yielding the greatest amount of dairy 

 produce ; the two intermediate zones, formed chiefly of quartzose 

 rocks, are inferior in population and in fertility ; they are the region 

 of landes and forests, in which all the iron furnaces are grouped 

 together. 



It is principally in the eastern part of Brittany that a large extent 

 of landes is found on the argillaceous-gravelly and pebbly tertiary 

 deposits. South of the Loire they all occur on these deposits, that 

 country containing no quartzose rocks ; and, I may add, most of the 

 forests of Normandy and Maine cover either the tertiary or quartzite 

 formations. That much wood and landes occur on the tertiary de- 

 posits arises in general from the very argillaceous nature of these for- 

 mations, which are too compact, and difficultly traversed by water, 

 or even wholly impermeable. Many of the soils that cover the 

 quartzites show the same influence, being also very argillaceous ; 

 though there are some with no argillaceous beds, when frequently 

 the soil, composed almost entirely of siliceous detritus, is too poor, 

 too dry, and thus with the contrary defect to that just now men- 

 tioned. This occasionally occurs on the top of hills formed of granite. 

 The landes observed on the quartzose or granitic formations are con- 

 stantly on high ground ; whilst those covering the tertiary deposits 

 are frequently in low situations. 



In the west of France the kind of cultivation and the species of 

 plants growing naturally vary from one formation to another. The 

 most striking differences are caused by the sandy or clayey nature of 

 the soil, by the presence of calcareous matter either existing naturally 

 or introduced artificially, and finally by the complex influence of the 

 vicinity of the sea. The schistose formations and the argillaceous 

 tertiary deposits show the greatest extent of pasture-land and those 

 beautiful meadows which charm the eye by their perpetual verdure, 

 thanks to the humidity of the soil ; but they are less adapted for fat- 

 tening horned cattle than the argillo-calcareous soils, where the pas- 

 ture is more rapidly restored, and which produce a greater variety of 

 plants, especially dicotyledons. 



The culture of buckwheat extends universally over every part of 

 western France that is composed of ancient rocks, and consequently 

 presents granitic, argillaceous or siliceous soils. Much less buck- 

 wheat is produced, and the cultivation of wheat and other plants, re- 

 garded as exhausting to the soil, is extended in the regions where the 

 activity of vegetation can be promoted by the use of lime, as chalk, 

 marl, shell or other calcareous sands, and thus in the maritime zone 

 or near the limestone formations. When quitting Brittany, we enter 

 the plains or plateaux of Normandy, in which the secondary lime- 

 stones crop out, the cultivation of the buckwheat is seen at once to 

 cease, and the aspect of the country undergoes a complete change. 

 The undulating surface of Brittany is divided into an infinite number 

 of minute fields, separated by ditches and hedges so covered with 

 trees that the country seems to the eye like an immense forest. On 



