Revieivs — A. Guiliier's Geology of the Sarfhe. 321 



Under the head of Primordial Silurian he ranges a series of schists 

 and flaggy beds with bands of dolomite, which are stated to occur in 

 certain localities between the Phyllades and the Gres Armoricain ; 

 but the only^fossil hitherto found is a Lingula which Dr. Davidson 

 identified with L. crumena, and this same Lingula is found in the 

 overlying series. 



The representatives of the Lower Silurian (Ordovician) are the 

 following : — 



3. "White sandstones without fossils (? Gres du May). 



2. Shales with Cdlymene Tristani. 



1. The Armoiican sandstone and red shales. 



The two lower stages are probably of Arenig age, No. 2, contain- 

 ing also CaJymene arago, Asaphus nobitis, Illceniis giganteus, Placoparia 

 Tournemmei, and Cheiriirus Guillieri. 



The beds of true Silurian age are (1) Sandstones and Carbonaceous 

 Shales with Graptolithus colonns ; (2) Shales with Cardiola interrupta. 

 We may notice that neither here nor in treating of the other Paleeozoic 

 groups are any estimates of their thicknesses given. 



Of the Devonian system only the lower portion is found, and this 

 consists of (1) Sandstone; (2) Shales; (3) Limestone, the last 

 being rich in fossils. 



A great break then supervenes, neither Middle nor Upper Devonian 

 nor the lowest part of the Carboniferous being represented. The 

 Devonian Limestone is succeeded by a series of sandstones and shales 

 which include beds of workable anthracite and a band of limestone 

 containing Producta gigantea — a series which is referable to the 

 upper part of our Carboniferous Limestone. No true Coal-measures 

 occur nor any strata of Permian or Triassic age. 



The succeeding beds are Jurassic and belong to the Middle Lias 

 (limestone with Pecten equivalvis, 18 feet) and to the Upper Lias 

 (marls and limestones with Am, hifrons and Am. serpentinus, thickness 

 24 feet). 



The Oolitic series is well represented, as shown by the following 

 tabular view : — 



KiMERiDGiEN. Limestone with Astarte minima. 



( Sandstone with Trigonia. 

 CoRALLiEX. < Oolitic Limostone. 

 ( Ferruginous sands. 



OxroRDiEN I ^^^J" ^""^ Limestone of Aubigne. 



( Clay and Limestone of La Vacherie. 

 Tallovien { ^srruginous Limestone with Am. coronatus. 



\ Clay and Limestone with Am. maerocephalus. 



( Montlivaltia Limestone. 



I Marls with Terebi-atula cardinm. 

 Bathonien. ^ Oolite of Mamers. 



I Lithographic Limestone. 



t Oolite with Rhynch. spinosa. 

 Eajocien i Oolite with Am. Farkinsoni. 



\ Oolites with Ter. perovalis. 



The Cretaceous rocks of Sarthe possess a peculiar interest because 

 they include the type of D'Orbigny's Cenomanien stage ; the beds 

 composing this stage are evidently shore deposits of the Cenomanien 

 sea and beds of sand with Bhynclwnella compressa, Terehratella 



DECADE III. — VOL. lY. NO. Til. 21 



