﻿10 



GEOLOGICAL MEMOIRS. 



Isola : to the eastward at Pirano it sinks gradually from the primitive 

 mountains to the sea, which however it never reaches. Here and 

 there it is broken through by abrupt ravines and covered by a luxuriant 

 vegetation. This is remarkably the case at an old saltwork near the 

 promontory called " Punta Ilonco," at which point the range of hills, 

 in whose escarpment the limestone is seen, turns in a landward di- 

 rection. It is very deserving of attention that the limestone is in- 

 variably attended by a greyish-blue marl which forms its roof, as has 

 been already observed of the upper beds of the nummulitic limestone 

 in the Karst hills. 



The main road from the saltwork to Isola leads from the lime- 

 stone bed up a hill, which consists of macigno dipping a little to the 

 south. On the summit the road leads for a few toises along the 

 marl, and then again the limestone with its numerous fissures appears 

 from under it, forming the covering of the hill, and reminding us by 

 its poorer vegetation of the barren limestone rocks of the Karst. 

 However, it is only necessary to descend a few paces by the foot-road 

 to Isola, to satisfy oneself that the limestone in question is merely 

 this single bed I have described, which here, near the chapel of 

 S. Maria of Loretto, covers the ridge of hills for some distance. 



Under it lie beds of macigno several hundred feet thick, which 

 form the sides of a semicircular valley, on whose northern extremity 

 stands the town of Isola, on a promontory at some height above the 

 sea. The bottom of the valley, as well as the promontory, consist 

 of grey hard nummulitic limestone, covered here and there with soil, 

 the junction with the macigno being covered with detritus. Plow- 

 ever, if it be borne in mind that the beds of the nummulite lime- 

 stone, like the macigno, are nearly horizontal, with a slight dip to 

 the south — that the macigno gives no evidence of a shifting of its 

 beds, and their original lines of deposition seem to have undergone 

 no considerable change — if it be remembered that in the limestone 

 not only a hot spring but also a cold spring of most unusual abun- 

 dance bursts out, which becomes very muddy by continued rains, which 

 circumstance, with great probability, connects this limestone with the 

 cavernous limestone of Inner Istria — (in which case it is demonstrable 

 that there is no water-bearing stratum between the Isola limestone and 

 that of Inner Istria, such as the macigno would have proved) — if 

 to these considerations be added, that here, as in other localities, the 

 stratum of macigno nearest to the limestone is a greyish-blue marl, 

 which has hitherto always been found overlying the limestone — all 

 this being considered, it is not hazardous to affirm, in the absence of 

 positive proofs, even without the analogy of the Opchinaberg, that 

 these macigno beds overlie the limestone, and are a newer formation ; 

 which the abundance of NummuUtes, now acknowledged as tertiary 

 fossils, would alone have made probable. 



Along the shore from Isola to Capo d' Istria this band of limestone 

 again appears in the macigno, but dips occasionally beneath the sea- 

 level. In this part it is thicker than in the previously described 

 localities, being usually about 9 feet thick : in all other respects it is 

 the same, so that only one spot deserves to be mentioned in the 



