298 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Jail. 4, 



water. In column No. 12 these forms are well represented by full- 

 sized individuals, though not in a large proportional number. 



Of the leading Rotalian forms, we have here some of the varieties 

 of Rotalia (Planorbulina) farcta that are usual in moderately deep 

 water ; so also of R. repanda ; the varieties of R. Beccarii are those 

 of deep water; the varieties of R. Turbo, which usually affects 

 shallow waters and sandy bottoms, are feebly represented here. 



The Nonionince, and their more highly developed relatives the 

 Polystomellce, seem, by the varieties here present, to indicate a 

 moderate depth. 



Of the opake-shelled Foraminifera we have here a few good 

 varieties of Miliola, inhabiting deepish water; the truly littoral 

 forms being almost wanting. Of the rest of the opake group, there 

 are some large helicine specimens of Lituola nautiloidea, and a few 

 smallish Cornuspirce, none of which inhabit shallow water. 



From the evidence thus gathered by a comparison of the contents 

 of column No. 12 with the Foraminifers of the existing seas and 

 oceans, we may conclude that these particular Siennese clays were 

 deposited at a depth of not less than about 40 fathoms, and not more 

 than about 100 fathoms. We must remember here that an area of 

 a clay-bed or any other sea-deposit may have a considerable ex- 

 tension under a gently varying depth of water, within certain limits ; 

 and that samples of the same clay-bed taken from within a few 

 miles, or even yards, of each other, may yield somewhat dissimilar 

 portions of one great well- characterized fauna. Thus we may take 

 our specimens from the spot where the littoral overlaps the deep zone, 

 or where the latter is sliding into the abyssal. The wide limit of 

 from 40 to 100 fathoms, indicated for the Siennese clays, illustrated 

 by column No. 12, may be thus accounted for. 



No. 13. Blue Clay from S. Quirico (Professor Meneghini). 



From the smallness of the specimens, and the proportional abun- 

 dance of Globigerina, this was very probably formed in a depth of 

 from 150 to 250 fathoms. 



No. 14. Blue Clay from Pescaja (Meneghini). 



This yields numerous small specimens of Rotalia Beccarii inter- 

 mixed with innumerable Entomostraca (Cy there Muelleri, var.). From 

 the small size of the Rotalia and the presence of this Cythere, we 

 may confidently interpret this clay as a deposit of shallow and pro- 

 bably brackish water. Both R. Beccarii and O. Muelleri are found 

 to range upwards into estuaries and salt-marshes. 



No. 15. Sand from Pienza (Meneghini). 



This is an Amphistegina-bed. It has a few shallow- water forms 

 besides the Amphistegina, especially Rotalia Beccarii and Polysto- 

 mella crispa, which are large and abundant. We best know Am- 

 phistegina, in the Canaries, West Indies, and Eastern Seas, in shell- 

 beds at from 20 to 40 fathoms. In the white mud from the Austra- 

 lian reefs (10 to 20 fathoms), dredged by Mr. Jukes, and rich in 

 Foraminifers, Amphistegina is large and common. We have not 

 met with a recent Amphistegina in the Mediterranean. 



