282 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



S.S.E. J N.N.W. 



Pescera R. S Marmolaio R. 





Gabbro rosso. Marls and gypsum. 



The beds have, at the mines, an inclination of about 5 degrees to 

 the N. W. or N. N. W., and consist of regularly alternating strata 

 of blue clay or matajone and grey gypsum, the latter containing 

 in regular layers nodules or spheroidal blocks of the pure white 

 alabaster. In the shaft of the mine I observed five distinct beds 

 of gypsum alternating with the blue clay, and varying in thickness 

 from five to twenty feet ; but as the owner, Signor Mazzoni, had no 

 measurements, and I had no means of obtaining perfect accuracy, 

 the numbers are probably understated. The only known mea- 

 surement was, that the whole depth of the shaft to the fifth bed 

 of gypsum was 1 10 braccie, or 200 feet, and in another mine the 

 fourth bed, which was here 20 feet thick, was there said to have a 

 thickness of 30 feet. 



The range of low hills in which the alabaster is found, is about 

 four miles in length along the strike of the beds from N. E. to 

 S. W., but the pure alabaster is only found near the centre of this 

 line, and three of the four mines now worked are on the small 

 property of Signor Mazzoni : nor does it extend far in the trans- 

 verse direction from S. E. to N. W., for about half a mile N. W. 

 the gypsum is of a very inferior quality, and dips under the blue 

 marl ; and the mines, though sunk to the depth of nearly 200 feet, 

 are rendered useless by the water having got in. 



We entered the mine by an inclined path, and, passing under 

 ground, soon reached an open well or large inverted cone, round 

 which the inclined path is carried, and where the section of marls 

 and gypsum is well exposed. As the descending road passes 

 through the third and fourth gypsum beds, galleries are seen 

 striking into the rock in all directions. The first and second 

 gypsum beds are of a uniform character and grey colour, and do 

 not contain any alabaster blocks. These are found principally in 

 the third and fourth beds, and occur as irregular isolated spherical 

 masses imbedded in the gypsum, from which they are, mineralo- 

 gically speaking, distinctly separated by a thin black crust, which 

 indicates to the workman the existence of the finer nodules. 

 These nodules are most frequent in the lower part of the stratum, 

 and occur in regular layers, never touching, although varying 

 much in their distances from each other. In bed No. 3. there are 

 two layers of these nodules, and in No. 4. there are three. They 

 vary much in size, weighing from 20 or 30 lbs. to upwards of 20001bs. 

 When the workman discovers the black crust, he is at once aware 



