14 THE EOCENE BEDS 



partly by the Seine on the south, and varying from fifteen or 

 sixteen miles wide at Provins to a mere point north of Epernay. 

 The other lake was situated to the south-east of Chartres, and 

 was, roughly speaking, forty miles long from north-east to south- 

 west, and fifteen to twenty miles across in a south-easterly 

 direction. That the Upper Calcaire Grossier had a more con- 

 siderable range is, however, shown by the outliers in various parts 

 of the Paris basin. 



Throughout this extensive tract the marine beds vary from 35 

 feet to 146 feet thick, and in almost every part contain an 

 exceedingly rich and interesting fossil fauna, to which reference 

 will be made in dealing with the details of the formation. 



This formation is the most important in the Paris basin, 

 not only from its interest in a geological and palseontological 

 sense, but also on account of its great commercial value, as from 

 it most of the important building stones of the French metro- 

 polis are obtained. 



The component beds of this formation are usually yellow or 

 buff in colour, passing by insensible gradations to a white, cal- 

 careous mass. Speaking generally, where the colour is of a 

 yellow or brownish tint sandy particles predominate, while the 

 whiter portions are almost wholly calcareous, either compacted or 

 in a pulverulent condition ; in any case but few extraneous 

 minerals, other than silex and carbonate of lime in an amorphous 

 state, are present in the Calcaire Grossier, occasional crystals of 

 carbonate of lime and quartz and flakes of mica being the some- 

 what rare exceptions. The Upper Calcaire Grossier (the Caillasses) 

 is of a more varied character than the Lower and Middle, as we 

 shall presently see. 



The lithological characters of the Calcaire Grossier, being 

 fairly constant for a particular horizon throughout the basin, 

 afford a suitable means of identifying the various levels. The 

 Lower beds are generally very coarse-grained, sandy, and calcareous, 

 compacted in p'aces into a soft conglomerate, with green and 

 black flints and grains of a mineral generally referred to glauconite. 

 The Middle zone is usually composed of fine-bedded soft lime- 

 stones, or loose calcareous sands ; but in certain districts, as at 

 Chantilly, the limestone is consolidated, and forms an excellent 

 freestone for building purposes, from which very large blocks are 

 obtainable. 



The Upper division is often of a complex character, with thin 

 bedded limestones, beds of clay, calcareous or siliceous sands, or 

 thin layers of horny flint and thin marls, many times repeated in 

 a single section, as at Vaugirard and elsewhere. This portion of 

 the Calcaire Grossier is without the practical value of the lower 

 beds, but it is of particular interest to the geologist from its 

 chemical and mineralogical complexity. Quartz is found in some 

 cases, as at Neuilly, with the angles developed in bi-pyramidal form 



