mcarpenter.chez-alice.fr/errata.htm -mcarpenter.chez-alice.fr/errata.htm -

also chert - flintlike form of quartz composed of chalcedony Oxford dict.

Reasoning:

chaille - Accident siliceux dans les calcaires marins ... se différenciant des silex par leur cassure mate non translucide ...

chert - 1. Mot anglais ... 2. Au sens restreint ... 3. Au sens anglo-saxon, r. sédim. siliceuse et accident siliceux formés surtout de colcédoine et/ou d'opale, d'origine chimique ou biochimique, le terme regroupant souvent, dans la pratique, les chailles, les silex, les jaspes, les silexites.

argile à silex - Formation argileuse souvent rougeâtre, contenant des silex et résultant de l'altération et de la dissolution sur place des craies à silex ...
[no mention of argiles à chailles as such]
[Dict de géologie, Foucault et Raoult]

The bilingual Dict. of Earth Science by Michel & Fairbridge, tho', gives:

argile à chailles - Oxford clay (Jura)
argile à silex - flint clay

I only hope the author wasn't confusing the English "shale" (bedded clay) with "chaille":

argile feuilletée - shale

The Penguin Dict of Geology says:

clay-with-flints - The residual deposit left after the solution weathering of chalk, usually in the form of a red-brown sandy clay with numerous unrolled flint nodules ...

chert - Cryptocrystalline silica which may be of organic or inorganic origin ... Flint is the variety of chert occurring primarily in the Upper Cretaceous and as detrital pebbles in the Tertiary. It has a conchoidal fracture, as opposed to the flat fracture of chert.

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Note added at 1 hr (2006-11-15 11:51:34 GMT)
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Note the following:
Révision du Dictionnaire des Sciences de la Terre, 3ème édition : MICHEL, FAIRBRIDGE et CARPENTER, Dunod, 1999 (ISBN : 2 10 004640 3) - recensement des erreurs et proposition des ajouts […]
p. 315 a. à chailles, chert-bearing clay (cf. Oxford Clay);
http://mcarpenter.chez-alice.fr/errata.htm

While the Ouèbbhe confirms that the Oxford clay formation contains chert, it might not be the most suitable term for a formation in France!


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Note added at 1 hr (2006-11-15 12:00:03 GMT)
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Then again, you might want to play safe, and there is Web-justification for "clay with (flints and) chert(s)":

The CLAY-WITH-FLINTS is highly variable and consists of heterogeneous red-brownish clay with numerous clasts, FLINT AND/OR CHERT, remains of a complex ...
www.swougs.org/field_trip_reports/branscombe_field_trip.htm...

On the interfluves lying to the west and south-west of that dividing line we find 'typical' CLAY WITH FLINTS AND CHERT, i.e. angular stones and blocks, ...
links.jstor.org/sici?sici=1478-4017(1960)1%3A28%3C89%3ATBOSDO%3E2.0.CO%3B2-T

stony clay (the CLAY-WITH-FLINTS-AND-CHERTS), containing chert. fragments derived from the Upper Greensand (Upper Albian) ...
doi.wiley.com/10.1002/jqs.753

a south-west to north-east running ridge which has a capping of CLAY-WITH-FLINTS AND CHERT overlying ...
www.countrysideinfo.co.uk/fire1.htm

There are even 3 different ghits for "clay with cherts":
Development during the early Cretaceous of a thick blanket of CLAY-WITH-CHERTS by weathering of the Jurassic chert-bearing limestones after withdrawal ...
bsgf.geoscienceworld.org/cgi/content/abstract/176/2/199

And there are 49 ghits for "clay with chert (fragments, lumps, etc.) in various constructions.

What you call "fence-sitting"!