Disintegrated Limestone 303 
During my wanderings I have come across several such sub- 
terranean streams but in no other instance have I been able to 
trace their exit. Of course at many places, especially near villages 
in the sierra, it is a common sight to see an abundant stream 
issuing from some cavity in the living rock, sometimes turning the 
big water-wheel of a flour-mill, only a few feet from its source. 
Doubtless owing to the great age of the limestone and the 
extreme alternations of temperature between tropical heat and 
winter frosts it must have undergone for countless centuries, many 
of the sierras near Ronda are in a very disintegrated condition which 
makes them particularly dangerous for climbing as will be seen 
in my accounts of taking sundry nests in this district. Rocks which 
are thus weathered assume most fantastic shapes and are frequently 
known to the people of the sierra by appropriate names. Some- 
times, near the very edge of a cliff a most inviting natural balcony 
will proffer itself as a point of vantage whence to get a good view 
of the precipice below. I was standing on one of these in the 
sierra north of Marbella and, anxious to examine a cavern which 
looked like a nesting-place, leant my weight on the natural parapet 
in front of me and craned over. Suddenly I felt a tremulous 
motion and by a great effort threw myself backward just as my 
stone balcony, weighing several tons, slipped off its ledge and dis- 
appeared with a roar several hundreds of feet down a singularly 
nasty precipice. It was my first experience of this sierra and 
caused me to make a vow to be more careful in future. 
Not far from the same cliff is a curious saddle-back or “nek” 
of uptilted strata joining two big hills. Centuries of denudation 
have caused the rocks and soil on either side to fall away until 
the track along the summit has been narrowed at places to a few 
feet. Such is the optical illusion caused by this spot that when 
crossing it, particularly on a windy day and with drifting clouds 
below, it is not difficult to imagine that you are on a razor-backed 
