John H. Coohe — Black Limestones of Malta. 363 



and veins that formerly occurred in those portions of the Lower 

 Coralline Limestone that were broken up when the upper deposits 

 of the district were swept away. As I shall afterwards show when 

 describing the occurrence of similar veins in the Gozitan beds, this 

 black crystalline variety of the basement rock is still very common 

 in the upper layers of that formation. In the Malta district to 

 which I have just been referring these upper layers have been 

 completely swept away, and nearly all traces of black veins have 

 thus been obliterated. 



In Gozo its mode of occurrence may be studied to the best 

 advantage in the Lower Limestone quarries that are situated on the 

 southern coast in close proximity to the church of the Madonna della 

 Kala, and immediately opposite the islet of Comino. Fragments of 

 a red as well as of a black variety ai'e strewn around the hillsides in 

 great number, while quantities of red and of black chippings are to 

 be found intermixed with the debris of the quarry. 



The sections that the quarrymen have cut, show that both varieties 

 occur in thin irregular veins of from one foot to three feet in thick- 

 ness, and from ten to twelve feet in length ; or as irregularly shaped 

 patches having diameters ranging from three to eight feet. In 

 some instances several smaller veins ramify from the main seam, 

 and after pursuing an irregular course of a few feet in a horizontal 

 direction, they break off abruptly. 



It is in and around the " Scutella " seam which forms the capping 

 of the Lower Limestone, that the greatest number of veins and 

 patches seem to occur ; they are, however, found in the underlying 

 divisions also. 



The different varieties of rock vary greatly in their lithological 

 aspects in different parts of the bed. In the upper divisions they 

 are of a coarse texture and granitic appearance, and their fossil con- 

 tents consisting of Orhitoides, Echini, and spines are plainly discern- 

 able ; but in the lower parts, their close fine grain causes them to 

 exhibit an exceedingly homogeneous appearance. Another locality 

 in which the red variety is extensively developed is the bottom of 

 the valley which is situated midway between Eas-el-Hecca and 

 Uied tal Assiri on the northern coast of Gozo. The torrent that 

 tears its way down the bed for a few occasional hours during the 

 rainy season has there laid bare the basement rock, and has exposed 

 a large patch of bright, red limestone that answers in every par- 

 ticular to the rock of which the numerous fragments that lie 

 scattered over the surrounding slopes, are composed. 



In common with the other rock fragments with which the country 

 is strewn, there can be no doubt but that these black and red 

 varieties were derived from the island's formations at a time when 

 the forces of denudation were much more active than they are at 

 present. The numerous oscillations of level that the islands bear 

 evidences of having undergone, and the extensive erosion to which 

 they were afterwards subjected by the combined action of frost and 

 rain, are probably to be accounted among the most potent of the 

 forces that assisted in planing down the islands' rocks, and in 



