11 A FLORA OP GIBRALTAR AND THE NEIGHBOURHOOD 



or more, the Queen of Spain's Chair, or Sierra Carhonera, 978 ft., 

 and the Sierra Lorca and x\lcadeza Crags, of lower elevation. 

 The surface soil is very largely a compact stony gravel, with con- 

 siderable beds of stiff clay, but it becomes sandy in many places, 

 and there are large stretches of sand near the coast. The surface, 

 especially on the hills, is intersected by numerous watercourses, 

 but excepting the Elvers Guadarranque and Palmones and some 

 of the streams from the Algeciras Mountains, they only run 

 during the rainy season, and in very dry years even the larger 

 streams dry up. An extensive marsh, partly saline, exists at 

 Palmones and Guadacorte, and perennial wells are numerous in the 

 sandy ground cultivated for vegetables near Linea and Palmones. 



Spain is connected with Gibraltar by a belt of sand about two 

 miles wide, extending from Gibraltar Bay to the Mediterranean. 

 The town of Linea lies across this, separating the Spanish portion 

 of the sand from the Neutral Ground. In the former region the 

 sand is undulating and very bare of vegetation, except where it is 

 irrigated for cultivation, but the Neutral Ground is flat, hardly 

 rising 10 ft. above the sea, and is far more fertile. 



The Rock itself is of secondary limestone, rising vertically to 

 a height of 1350 ft. from the North Front (the highest point being 

 1439 ft., about IJ mile further south), and sloping steeply on its 

 western face, at the foot of which lies the town. The limestone 

 is full of hollows and pot-holes, and several extensive caves exist ; 

 the hollows are filled with a fertile soil, but from the nature of the 

 rock they very soon get dry. There are no permanent water- 

 courses, nor even temporary ones, except during the actual fall of 

 heavy rain, and there are no marshes. Here and there on the 

 lower portions, as about the Alameda and Windmill Hill, a 

 reddish sand appears, and on the eastern side, which in its upper 

 portion is precipitous, lies a steep slope of blown sea sand, which 

 supports a scanty but characteristic vegetation. 



Climate. 



The mean maximum temperature in July and August, the 

 hottest months of the year, is S-i'^, the mean minimum then being 

 75°, while maxima over 90° are not infrequent. ••= In January and 

 February, the coldest months, the means are 63° and 55° respec- 

 tively. Frost very rarely occurs, and only on the higher or more 

 exposed parts, though records exist of ice an inch thick on 

 shallow pools, which, however, soon disappears in the sun. 



The annual rainfall averages 28-5 in., but varies from 15 in. to 

 60 in. or even more. Of this the bulk falls between November 

 and April, the months of June to August rarely receiving a total 

 of 1 in. Kelaart records twenty-five consecutive years when no 

 rain fell in July. The effect of this climate is that, botanically 

 speaking, spring begins in November, the most floriferous months 

 being March to May, after which all the annuals are dried up ; in 



* The mean minima seem too high, but I have not been able to check them 

 by official records. 



