118 GEOLOGICAL MEMOIRS. 



(1.) The conglomerate which forms the lowest member of the 

 cretaceous formation is generally composed of greyish flints, and 

 black or greyish fragments of limestone, and seems entirely derived 

 from the degradation of the oolitic rocks. There are 80 or 100 

 yards of these conglomerates. 



(2.) Immediately overlying the conglomerate is a fine grained 

 sandstone containing mica, cemented by argillaceous and calcareous 

 marls, the sandy beds being separated by thin marls. The whole 

 thickness of the sandy group probably exceeds 100 yards, but the 

 different beds are thin. The colour varies from bluish grey to 

 yellowish, and rounded lumps of easily decomposing pyrites are 

 found occasionally in it. 



(3.) The Nummulite limestone is often compact, and its fracture 

 sometimes conchoidal ; but it more frequently contains marly frag- 

 ments, and even becomes a breccia. Fossils abound in this lime- 

 stone, but are not easily recognised, with the exception of the 

 Nummulites, which are distinctly seen on the weathered surfaces. 

 The thickness of the nummulite beds varies from half a yard to 

 two or three yards, and the whole thickness of the series is about 

 80 yards. 



(4.) The marls, which in Lombardy form the uppermost beds of 

 the cretaceous series, are of a red or blue colour, and either very 

 fissile and slaty, or more compact and solid, passing in the latter 

 case into a red marly limestone, of which the mineralogical cha- 

 racter resembles that of the red limestone of the oolitic series. 

 The total thickness of these variegated marls is between fifty and 

 sixty yards. 



It is worthy of notice, with regard to the subdivisions of the 

 cretaceous formation in Lombardy, that the Hippurite beds, and 

 those containing fucoicls, which in the south of France belong 

 especially to the lower part of the series, are in Brianza intimately 

 united with the nummulitic limestones, which in the maritime 

 Alps are upper cretaceous rocks. It may hence be concluded, that 

 the Monte Viso system of disturbances of M. E. de Beaumont has 

 not extended to the meridian of Milan, so that the deposition has 

 therefore been uninterrupted from the Hippurite to the Nummulite 

 period ; and M. Constant Prevot has already noticed this con- 

 temporaneity of Hippurites and Nummulites in Sicily. It is also 

 to be remarked, that since the Nummulitic limestone of the south- 

 ern Alps has suffered the dislocations of the Apennine system, 

 there is this additional proof of the bed being of the true cretaceous 

 period. The cretaceous beds above described exhibit amongst 

 themselves no strongly marked separations, but seem to pass in- 

 sensibly into one another. 



3. Tertiary Rocks. 



The only indications of marine tertiaries in Northern Lom- 

 bardy consist of small patches of blue marl in the neighbourhood 

 of Varesc. The best known of these is exhibited in horizontal 



