The amount of precipitation varies greatly for the different desert stations, usually becoming less as one goes south from the High Plateau. As has already been mentioned, the average rainfall at Laghouat, which lies at the southern base of the Saharan Atlas, is 198 mm., the average at Ghardaia is 114 mm., while that at El Golea is 47 mm. The latter station is about 225 miles south of Laghouat, in the midst of the Sahara. The amount of rainfall, however, is greatly influenced by altitude, although lack of adequate precipitation data for the desert makes impossible a detailed presentation of this phase of the subject. As the amount of the yearly precipitation is less in the extreme southern part of Algeria than it is nearer the Saharan Atlas, where the altitude also is greater, it might be expected that the number of rainy days would vary in a like manner. Such records as are at hand, however, do not show this to be the case. For instance, at Ouargla rain falls on an average 14.2 days, average of 7 years, while the rainfall is 90.2 mm.; yet at El Golea, with a rainfall of 47 mm., there are 23.4 rainy days each year.[4] On the desert the rains are often of a torrential nature, as facts presented above would indicate, and sometimes as much rain falls within a few hours, or even a few minutes, as usually occurs in an entire year. How much of the annual precipitation is of this character and how much is of the non-torrential kind the usual summaries leave entirely out of the account. It is well known that the former type of storm is more destructive and less useful to plants than the latter type. To illustrate the irregularity of the rainfall in the northern Sahara the monthly precipitation at Ouargla for several years is presented in table 2. TABLE 2.—_Rainfall at Ouargla, in millimeters._ +----+-----+-------+----+----+----+-----+----+ | | |No. of | | | | | | |Year| Amt.| days |Jan.|Feb.|Mar.| Apr.|May | | | | rain | | | | | | +----+-----+-------+----+----+----+-----+----+ |1900| | 1 | | | | | | | | | | | | | | | |1901| | 18 | | | | | | | | | | | | | | | |1902| 70.5| 8 | | |11.3| | | | | | | | | | | | |1903|135.6| 14 |55.0| | | | | | | | | | | | | | |1904| 35.0| 26 |20.0| | | | | | | | | | | | | | |1905| | | | | | | | | | | | | | | | | |1906| | |15.0| | 2.0| 4.0| | | | | | | | | | | |1907|210.0| 18 | |68.2| 67|325.0|16.2| +----+-----+-------+----+----+----+-----+----+ [**Continued]