Intelligence and Miscellaneous Articles. 409 



ON THE POLISHED ROCKS OF FONTAINBLEAU. 

 BY M. DUROCHER. 



In the Comptes Rendus de VAcademie des Sciences, for July 12, 

 1841, we find a " Notice on the traces of polishing which the dilu- 

 vium has left on the sandstones of Fontainbleau," by M. Durocher, 

 of which the following is a translation. 



In the places where the diluvium of the valley of the Seine has 

 extended, following the general direction 'from east-south-east to 

 west-north-west, those marks of polish which are seen so frequently 

 and so distinctly in Scandinavia and in the Alps, had not hitherto 

 been observed on the surface of the rocks. This is probably occa- 

 sioned by the soft nature of the rocks which form the Paris basin, 

 and their mechanical disaggregation under the influence of exterior 

 agents. It is the same in the countries to the south of the Baltic, 

 on which the diluvium of the north has formed thick deposits of the 

 fragments of the Scandinavian rocks : as only schists or limestones 

 are found in them, it is not possible that the marks produced by 

 the passing of the currents should have been preserved to our times ; 

 and yet their existence cannot be called in question ; for in boring a 

 well through the diluvial soil in Prussia, on reaching the solid rock 

 it was found polished and grooved as in Sweden and Finland : the 

 deposit which covered it had served as the means of preservation. 

 The absence of these traces in many places which have been the 

 theatre of diluvial phenomena, is therefore to be attributed to atmo- 

 spheric action. 



Amongst the formations which constitute the Paris basin, the 

 sandstones alone appear to me capable of preserving any remains of 

 diluvial impressions : in an excursion which I recently made to Fon- 

 tainbleau, I indeed recognised that these marks were not entirely 

 effaced. In the forest of Fontainbleau there are but very few spots 

 where this can be observed ; the principal cause which hinders this, 

 is, that the solid sandstone seldom appears at the surface in great 

 areas. It^s almost everywhere covered with a vegetable crust, and 

 unfortunately in the small number of cases where it may be seen, it 

 is nearly always disaggregated and reduced to sand. As to the 

 blocks which are found heaped up in such great numbers and pro- 

 digious size, it is difficult to discern upon their surface the marks of 

 the currents of water which displaced them, and gave them their 

 various and fantastical forms. It is only in the spot well known by 

 the name of the Gorges de Franchard, that I was clearly able to re- 

 cognise the traces of the passage of great masses of water. 



I will endeavour to notify, as precisely as possible, the points where 

 I observed it most distinctly. In following the road which leads 

 from the Cross of Souvray (on the road of Ury) to Franchard, when 

 we reach the spot where this road makes a slight deviation to the 

 north-east, we" must take the road which leads to the Rochers-des- 

 hautes-plaines, and turn at the third path to the right : this crosses 

 a small plain covered with heath, and leads straight to the defile of 

 Franchard. It opens into the principal valley by a slightly inclined 



