4 GEOLOGICAL MEMOIRS. 



" 4. A succession of strata of yellowish marly limestone and olivi^ 

 yellow schists, containing impressions of fucoids. ''^ 



" 5. A series of strata of light grey limestone with flint, containing 

 a few Ammonites ; this formation losing the flints in the lower part, 

 and acquiring colour, passes into — 



" 6. Red ammonite limestone rich in Entrochi, &c. 



" 7. A whitish limestone, the stratification of which is seldom seen, 

 but in some places appears unconformable to the former beds ; it 

 contains a few bivalve and turriculated fossils. 



" 8. A stratified deposit of a dark ash-coloured limestone without 

 flints, in which hitherto no fossils have been found, and which in 

 many places passes gradually into the former. 



" Secondl?/, That the foregoing series of beds, from the dark grey 

 limestone with flints down to the red ammonite limestone inclusive, 

 pass into one another, both by mineralogical and geological transi- 

 tion ; and 



" Thirdly/, That the red ammonite limestone is visible in some 

 localities and not in others ; that in some places it occurs without 

 any modifications, and then it rests on the white limestone without 

 passing into it; whilst in other places it is altered, and then almost 

 imperceptibly passes into the underlying limestone, containing bi- 

 valve and univalve fossils." 



In the next chapter (Chap. III.) the author compares the rocks of 

 the Monti oltre Serchio with those of the Monti Pisani, from which 

 it appears that the latter consist of the same series of formations as 

 the former, with the addition of the Verrucano not visible beyond 

 the Serchio. This verrucano underlies the lowest calcareous de- 

 posit ; it is a siliceo-talcose rock, sometimes resembling anagenite, 

 sometimes talcose schists, and forms the lowest portions of all the 

 stratified deposits of Tuscany, and is often altered into nodular stea- 

 schist, or a kind of gneiss. In the limestone which rests on the 

 Verrucano is the deposit of limestone without flint, in which are the 

 celebrated quarries of statuary marble of Carrara and Seravezza, 

 containing Pentacrinites and fossil univalves. 



In chapter IV. the author has attempted to classify the forma- 

 tions which compose the Monti Pisani, although in consequence of 

 the scarcity of fossils, and the numerous disturbances to which these 

 formations have been subjected, he considers it a most difficult and 

 abstruse question. With this view he enters into a close examina- 

 tion of those characteristics by which formations are distinguished 

 from one another, viz. 1. Direction or dip of the beds. 2. Uncon- 

 formability of stratification. 3. Transition by alternating beds from 

 one series to another. 4. Existence and nature of the fossils. The 

 two former of these characteristics offer no results of importance in 

 determining the age of the diflferent beds. 



The author then gives a list of localities where the geological 

 transitions of the different formations may be observed, from the 

 alberese and macigno down to the verrucano itself, and arrives at 

 the conclusion, that all these formations are conformable in stratifi- 

 cation, and, consequently, that they must be considered as having been 



