146 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [XoV. 21, 



tioned rests on red marl and feiTuginous sands, also belonging appa- 

 rently to tlie subcretaceoiis series, and resting nnconformably on the 

 jui'assic limestone of Coimbra described farther on. 



At Condeixa the subcretaceous beds are overlaid by an extensive 

 deposit of travertine, which is spread out in iiTegular patches over 

 the low country for many miles round that town ; in many places 

 the travertine is twenty or thuty feet thick ; it consists of a variable 

 mixtnre of sand and hme brought down by the streams of water which 

 traverse the beds of sandstone and limestone of the neighbouring hills 

 and break out in powerful springs at their base, the sand being rolled 

 down by the streams and then united by a compact cement of Ume 

 which had been held in solution in the water. 



The travertine appears to have been forming fi'om a remote 

 period down to the present time ; in the neighbourhood of the 

 springs it may be seen newly formed and quite soft ; below this it 

 forms a sohd rock, and the lower and older beds are so hard that 

 they are extensively quarried for millstones, which have a great re- 

 putation all over Portugal : some of the lower beds contain many 

 stems and impressions of the leaves of dicotyledonous plants. 



From Coimbra to the sea the Mondego runs through a broad 

 marshy valley with many lateral branches of considerable extent ; 

 these, like the main valley, are on the line of great faults : hence the 

 sections which may be obseiwed in the hills enclosing the river have 

 a want of regular coimection, I followed the north bank along the 

 line of section No. 2 (tig. 3). 



The Jurassic limestone of Coimbra is overlaid imconfonnably, as has 

 been already mentioned, by red sands and marls with some subor- 

 dinate beds of hmestone, in one of which at San Fagundo three 

 species of Tyhstoma are abimdant : this is covered to the westward 

 by sands and loose sandstone, containing occasional beds of limestone, 

 with a veiy shght dip westward : the only shell observed in these 

 beds was Exogyra conica, which is very common in most of the hme- 

 stones. Similar beds continue to Montemor-velho, where they are 

 interrupted by a ridge of limestone hills nmning from the bank of 

 the !Mondego to the X.X.E., on which the subcretaceous beds rest 

 unconfoimably with a dip of 3" TV. The limestone of Montemor- 

 velho is of the age of the has or of the lower part of the oohtic series. 

 On the west side of the ]\Iontemor ridge is a flat marsh, on a line of 

 fault, beyond which we again come to the subcretaceous sandstones 

 dipping N.^. 30", and containing a bed of limestone about 100 feet 

 thick with abimdance of shells of the genus Tijlostoma ; this is pro- 

 bablv the same bed as that seen near Coimbra at Condeixa and San 

 Fagundo. Beyond the Ponte de Mayorca, which crosses a broad 

 marsh following the line of an important fault, hes a thick formation 

 of limestone near the village of Mayorca; this I failed to examine 

 owing to the night coming on, but M. Bonnet, who had resided for 

 some months in this part of the comitry, informed me that it is the 

 continuation of the hmestone of Cape Mondego, which I shall shortly 

 show to belong to the middle of the oolitic period. 



The limestone of Mayorca is overlaid by a thick deposit of feiTu- 



