116 GEOLOGICAL MEMOIKS. 



is one of much interest as connected with the disturbances of the 

 older and middle secondary period, and the elevation of the Alpine 

 chain ; and, as M. de Collegno spent three summers in the country, 

 and has been a careful and minute observer, an account of his 

 paper will be of value to the English geologist, and more espe- 

 cially to the traveller crossing any of the principal passes of the 

 Alps to visit the Italian lakes. 



The sedimentary rocks appearing in the Lombardic Alps are of 

 three geological periods ; viz. the Oolitic (including the Lias), the 

 Cretaceous, and the newer Tertiary. On crossing the Simplon or 

 the Splugen passes the stratified rocks may be seen near the axis 

 of the Alpine chain, apparently conformable, and even alternating 

 with crystalline rock; and the fossils (Belemnites, &c.) found in 

 the beds thus associated with gneiss, show the oolitic origin of the 

 formation, although there can be little doubt that the modifications 

 of the oolites attain their greatest extent in this part of the chain. 

 To the north of the Lake of Como, saccharoid limestones dip away 

 at an angle of 60° or 70° to the south, and repose on, or even pass 

 into the gneiss, the limestone containing a quantity of mica at the 

 junction. Towards the west the appearance changes, and the 

 dolomite becomes fossiliferous ; but here also the rocks in imme- 

 diate contact with those sometimes called primitive (granite, gneiss, 

 &c.) are unquestionably of the oolitic period. 



1. Oolitic Rocks {including Lias). 



The oolites of the district we are considering may be sub- 

 divided into five groups, the lowest of which (l.)is a red sand- 

 stone, passing into a conglomerate, and sometimes into a breccia, 

 of the same colour : its thickness is very variable, and it often con- 

 tains quartz flints and fragments of gneiss and granite, but no 

 mark of organic remains. 



(2.) A black bituminous limestone, more or less schistose, and 

 often so compact as to be used for marble, rests on the red con- 

 glomerate. It has been greatly disturbed and cracked since its 

 deposition, and its thickness cannot be well ascertained, but it 

 appears to be considerable. This bed is sometimes dolomitic, 

 sometimes so bituminous as to give out a strong odour when struck, 

 and sometimes so argillaceous as to become fissile, and even slaty. 

 It contains fossils, the remains of fishes having been found in it, 

 and even fragments of reptiles allied to Plesiosaurus. Univalve 

 shells, resembling Melania, have also been met with in great 

 abundance near Esino. 



(3.) A greyish limestone overlies the black limestone, and is 

 much more uniform in its character. It is remarkable for gener- 

 ally containing siliceous or cherty bands and thin beds of sandy 

 marl. The colour of the limestone rarely varies, except on ex- 

 posure, when it sometimes changes to a decided white. It does 

 not seem to attain a greater thickness than about 200 yards, but it 



