the Environs of Paris. 27 



forms between the Sarthe and Loire, and extends a little to 

 the north of the first of these rivers. 



These sands might at first sight be taken for an alluvial 

 soil, the rather because, from their want of adherence, the 

 higher parts have been disturbed by water, and are often 

 mixed with rolled pebbles ; but when these countries are 

 tnore carefully studied, we are soon convinced that they 

 belong to the ancient chalk formation ; the chalk becomes 

 coarser and contains more sand the deeper it gets, and the si- 

 liceous nodules often pass into the state of calcariferous sand- 

 stone. This sandy chalk is afterwards seen to alternate with 

 regular beds of sand and sandstone, containing fossils charac- 

 teristic of the ancient chalk, and the principal mass of the 

 sandy rock can be distinctly recognized to dip under the 

 chalk. These sands and sandstones commonly contain cal- 

 careous matter, and sometimes chlorite ; there are some 

 however altogether pure : the greater part are fine grained 

 and uniform, others are of inequal grains ; their colour is 

 commonly yellowish, sometimes whitish, rarely blue, red, 

 or ferruginous. This last colour belongs principally to the 

 sandstone beds passing into puddingstone, named roussard 

 by the country people, and which occur in the midst of the 

 sands. Organized bodies are not generally found in the 

 purely quartzose beds, but they are often very abundant ia 

 those containing calcareous matter ; the most common are 

 the orbicular gryphite, and some species of oysters. Am- 

 monites begin to appear, or, to speak more correctly, this 

 rock appears to be the last term of this animal's existence ; 

 it is probable however that when the species of this genus 

 shall have been better studied, the ammonites of this epoch 

 •will be found to differ from those of the alpine limestone ; 

 the remains of fish and the impressions of vegetables are 

 also found in it.* 



* This last observation is due to the zeal of M. de Maulny, naturalist 

 of Mans. 



I ought to remark before I quit this country, that I do not consider that 

 all the sand covering the platforms between the Sarthe and the Loire, 

 belongs exclusively to the chalk formation; for the presence of thin mill- 



