2 GEOLOGICAL MEMOIRS. 



3. Light grey limestone with flint, and red ammonite limestone. 



4. Limestone with bivalve and turriculated (univalve) fossils. 



5. Verrucano. 



The author then describes the first of these groups, consisting 

 of Alberese limestone and arenaceous macigno, with which the 

 argillaceous schists alternate. The Alberese does not occur in the 

 mountains of Pisa, nor is the macigno there extensively developed ; 

 the absence of the former, generally abounding in fucoids, and 

 sometimes containing nodules of flint and beds of nummulites, is 

 probably owing to the absence of the upper portion of the macigno, 

 on which it always rests. The strata of the macigno have under- 

 gone great disturbance and dislocation ; they are generally of an ashy 

 colour and of a compact grain. Under the macigno are the beds 

 of argillaceous schist, the lowest of which again alternate with bands 

 of limestone and macigno. This lower portion of the macigno 

 being as yet but little known, the author describes the varieties of 

 limestone in it, and the alternations of strata connecting them with 

 it and with the schists. 



In the valley of Filettole occurs the following section in descend- 

 ing order : — 



1. Macigno in thick strata, interstratified with thin argillaceous 

 schists of an olive-grey colour. 



2. A thick bed of friable olive-grey schist. 



3. Whitish limestone, compact and homogeneous. 



4. Olive-grey schist. 



5. Thick beds of grey limestone with a rough fracture, to which 

 the author applies the term calcaria screziata^ variegated or mottled 

 limestone (bigarre of the French). 



The following section occurring near Monte di Quiesa is given 

 as an instance of the passage of the macigno into the underlying 

 limestone : — 



L Macigno in thick beds. 



2. Marly argillaceous schists of an olive-grey colour, dark and 

 slightly veined. 



3. Macigno. 



4. A mass of schistose beds passing into galestro. 



5. Band of variegated limestone. 



6. Schistose galestro. 



7. Variegated limestone containing nodules of flint. 



8. Thick stratified mass of galestro, dark or liver-red, joining 

 the variegated limestone, and gradually passing into grey limestone 

 with extensive beds of flint. 



After adducing other instances, the author shows " that the schists 

 underlying the macigno are perfectly conformable with it, being 

 imperceptibly connected with those beds which alternate with the 

 beds of the macigno itself, and connect this formation with the various 

 kinds of limestone which underlie it." (p. 14.) 



The author then describes the variegated limestone (calcaria 

 screziata) ; this is almost universally without flint, and fossil remains 

 are, if not absolutely, at least almost invariably wanting ; but in the 



