56 NATURAL SCIENCE. July. 



land, dotted with lakes and old lake basins, and sinking in places 

 below the level of the sea." It may be traced along the Red Sea, 

 itself like a magnified fjord, up the Gulf of Akaba, and on through 

 the Dead Sea and the Jordan Valley, till it ends on the plain of 

 Northern Syria, after a course of about 4,000 miles. The trough-like 

 form of this sunken district is maintained throughout, and scattered 

 over its floor is a series of over thirty lakes, of which only one has an 

 outlet to the sea. A glance at the sketch-map in Dr. Gregory's 

 volume at once recalls to memory the outline presented by more than 

 one series of volcanic vents in the Pacific and Indian Oceans ; and 

 this African district, as we have seen, "is a line of eruptive 

 disturbances as well as of faulting. In the Rift region the effect of 

 the latter process has been no less remarkable than unusual. Strips 

 of country have been dropped down by a series of parallel faults, and 

 thus a valley has been formed with precipitous and sometimes step- 

 like sides. Here, then, the valleys often are due to rifts instead of to 

 erosion ; the mountains occasionally are formed of blocks instead of by 

 folds, and in some cases the great earth movements have happened 

 so recently that rock scarps 1,000 to 2,000 feet in height still stand 

 bare and precipitous as though broken but yesterday, and straight 

 lines and sharp angles still dominate the scenery. 



Dr. Gregory believes that the making of the Rift Valley system was 

 heralded by intense volcanic activity, when first trachytes, then 

 andesites, were ejected. This probably occurred in some part of the 

 Cretaceous period, and was followed in the Eocene by the first of the 

 series of north and south faults which ultimately formed the Rift 

 Valley. Afterwards, probably in the Miocene, came a second series 

 of plateau eruptions (basaltic). Another series of faults, in the same 

 general direction as the earlier one, occurred in the Pliocene, when 

 some of the lake basins were formed, while to the Pleistocene are 

 referred the more recent volcanic eruptions (such as the crater of 

 Kilima-Njaro, with a few cones which still give signs of activity), the 

 last series of Rift faults, and the modern lakes. The basins of these 

 are partly the result of differential movements athwart the general line 

 of subsidence. 



In connection with this subject Dr. Gregory makes some remarks 

 upon the Jordan Valley and the Dead Sea, for these have an important 

 bearing upon certain questions of zoological distribution. He 

 believes that in former times a river flowed southward, from Palestine, 

 along that part of the Rift Valley which is now occupied by the Red 

 Sea, and entered the Indian Ocean near Aden. Probably this river, 

 not far from its mouth, was joined by another from the Rift Valley, 

 so that the equatorial lakes were in water-communication with the 

 Jordan, and their fish could reach Palestine without entering the Nile. 

 Dr. Gregory seems to shrink from claiming the Arabah as only a 

 prolongation of the ancient valley of the Jordan, but he goes so near 

 to it that we anticipate he will before long accept this as the simpler 

 solution. Incidentally, also, he discusses the significance of that 

 singular valley, the plain of Esdraelon, which severs northern 

 Palestine and communicates with the valley of the Jordan by gaps, 

 which are only about 300 feet above sea-level. He explains these, 

 rightly in our opinion, as cases where one valley has been 'beheaded' 

 by another, a thing of frequent occurrence in the Alps, but we doubt 

 whether the streams flowing towards the Kishon have trespassed on the 

 heads of the glens draining into the Jordan. As the fall to that river 

 is at least three times as great as it is to the sea, and the course of 

 the streams is much shorter, we think that these would be the 



