1853.] 



RIBEIRO AND SHARPE-^BUSSACO. 



141 



lowish, and black schists, semi-crystalline limestones, and carbona- 

 ceous schists. It contains an abmidance of Trilobites and shells, which 

 are most plentiful in a very dark greywacke or micaceous schistose 

 sandstone, with well-marked bedding, which occurs in the middle of 

 the formation. The Trinuclei are only found in this rock. Orthis 

 Berthoisi has been found at Portela de Loredo in the schists with 

 Ti'inucleus, Phacops, &c. The Asaphi, Calymenes, and Illcsni are 

 frequent in the beds which rest on the quartzite, and are accompanied 

 by several species of Ot'this*. 



Middle Division of the Silurian Formation {Lower Silurian) . — An 

 ochreous argillaceous rock of metamorphic character is found resting 

 on the beds just described in several localities along the middle of the 

 Silurian district on a line of N. 35° W. to S. 35° E., always accom- 

 panied by greenstone or diorite. In some few localities it contains 

 hollow impressions of Orthis, Leptcena, &c., mixed with a great 

 abundance of small branching corals. The rock is hard and yellow ; 

 it splits up into prisms, and the bedding can only be distinguished by 

 the layers of hollow impressions of the organic remains. From its 

 peculiar mineral character it might be called Argilolite; in some 

 places it seems to pass insensibly into the diorite with which it is as- 

 sociated. The irregular manner in which these small patches of 

 ochreous rock occur would leave it difficult to assign its true geolo- 

 gical position but for the assistance of its organic contents, which 

 clearly refer it to the Lower Silurian epoch ; and it will be seen by 

 the list of species that several are common to this and the lowest 

 division of the Silurian formations just described. 



The diorite occurs at intervals for about five leagues in several 

 localities, which are marked on the map, following a line of about 

 N. 35° W. to S. 35° E., disturbing the Silurian rocks which it breaks 



* Organic Remains of the lower division of the Lower Silurian Rocks : — 



Illaeniis giganteus, Burm. pi. 3. f. 10. 



/. Lusitanicus, Sharpe, Journ. Geol. 

 Soc. V. t. 6. f.l. 



/. Desmaresti, Rouault, Bull. Soc. 

 Geol. Fr. 2 ser. vol. vi. t. 2. f. 2. 

 Phacops Dujardiui, Rouault, Bull. Soc. 



Geol. Fr. iv. t. 3. f. 5. 



prosevus, Emmerich, Burm. t. 4. 



f. 3. P. socialis, Barrande. 

 Phacoparia Zippei, Boek. 

 Calymene Tristani, Brong. 

 Arago, Rouault, Bull. Soc. Geol. 



Fr. vi. t. 2. f. 3. 

 Trinucleus Pongerardi, Rouault, Bull. 



Soc. G.Fr. 2ser.t. f. 

 Ogygia glabrata, Salter, n. s. 

 Beyrichia Bussacensis, Jones, n. s. 



simplex, Jones, n. s. 



Redonia Duvaliana, Rouault. 



Deshayesiana, Rouault. 



Nucula Gestae, n. s. 

 Cise, n. s. 



Nucula Ribeiro, n. s. 



Ezquerrae, n. s. 



Eschwegii, n. s. 



Maestri, n. s. 



Beirensis, n. s. 



Bussacensis, n. s. 



Leda Escosurse, n. s. 

 Dolahra ? Lusitanica, n. s. 

 Cypricardia Beirensis, n. s. 

 Modiolopsis elegantnlus, n. s. 

 Orthis Ribeiro, n. s. 



Bussacensis, n. s. 



fissicosta ? Hall, t. 32. f. 7. 



basalis. Balm. 



testudinaria, Balm. 



parva. Pander. 



Pleurotomaria Bussacensis, n. s. 

 Ribeiria pholadiformis, n. s. 



Bellerophon trilobatus, SU. Syst. 



carinatus, Sil. Syst, 



Theca Beirensis, n. s. 



l2 



