286 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



the tomb called " tomba della vigna grande," the series of beds was 

 rather different. 



In a ravine, one mile north-west of the town, the blue clay is well 

 exposed, and is of considerable thickness. In it numerous shells are 

 found — Cerithium, Serpula, Dentalium (2 sp.), Venus, Cardium, 

 Area, Pecten, Natica, Pleurotoma, Cancellaria, JVassa, and 

 others. The same clay beds are well exposed on the road to 

 Cetona ; and, again in the neighbourhood of Sarteano, equally 

 rich in marine testacea. Between Sarteano and Chianciano, 

 Cardium is found in the sandstone tuff. Chianciano is celebrated, 

 in the annals of Italian Geology, for the great abundance and 

 variety of its tertiary marine shells, which occur in one or two 

 localities near the town. 



From Chianciano the same tertiary formation extends to Monte 

 Pulciano, offering sections of gravels and sands, containing beds 

 of oysters. Monte Pulciano itself stands on a lofty insulated hill 

 of sandstone and gravel. In the sand are many large Ostrese, and 

 a few Cerithia occur in the nodular calcareous concretions. The 

 formation is traversed by a few almost horizontal beds of very 

 hard sandstone. To the north of Monte Pulciano is the commence- 

 ment of a bleak and arid blue marl district, resembling that 

 so remarkably developed in the neighbourhood of Pienza and 

 S. Quirico, and with which the district of Monte Pulciano and 

 Chiusi was, in all probability, formerly connected. 



2. Tertiary Freshwater Formation. 



I now proceed to describe those localities in which tertiary 

 freshwater formations came under my observation. 



On the range of hills which I have been just describing, between 

 Cetona and Sarteano, the road crosses a spur of limestone rocks, 

 which, from its compact character, colour, and honeycombed ap- 

 pearance, I at first attributed to the Scaglia formation of the se- 

 condary or cretaceous period. But, on reaching the summit of an 

 elevated table land, I found in it numerous tertiary freshwater 

 shells, as Planorbis and Limncea. It rests against the secondary 

 rocks, and appears to be overlaid by the blue marls containing 

 marine shells. 



Another locality, where the same rock occurs, is in the valley 

 of the Bultino, two or three miles south-east of Colle, on each side 

 of which are extensive remains of a tertiary lacustrine formation, 

 through which the valley has been cut, and a large plain has 

 been excavated. The lower beds are very arenaceous, and contain 

 calcareous nodules. Near the village of Campigliano is a good 

 section, where some of the upper beds are of a slightly reddish 

 colour ; but, in general, they have the dull grey appearance of an 

 earthy alberese, sometimes assuming a concretionary character. 

 The upper beds contain Limncea and Planorbis. This formation 

 extends to Colle, forming a flat, level plain covered with barely a 

 foot of soil. 



