1888. | NEW YORK ACADEMY OF SCIENCES. 169 
showing that there was once a chain of lakes along the wadi. 
The main mass of the chain is a pink syenite, or gray granite, 
but it is everywhere rent by great convulsions of the age of 
igneous action, and injected with seams and dykes of green and 
black diorite, and red, gray, yellow and purple porphyry. These 
dykes often extend for many miles across the spurs of the chain, 
traversing the intervening wadis, and can be traced by their 
sharply defined margins and vivid coloring, which is not obscured 
even by a lichen. 
Toward the northern portion of the range the granite is over- 
laid by gray, red, white, and black sandstone. ‘lhe westetn 
flanks of the peninsula are all composed of jagged peaks, 
carved out of these sandstone rocks. Nothing could be more 
striking than the contrasts at every turn between whole moun- 
tains, one white, one black, one red and one gray, often touch- 
ing at their base, and other mountains with straight or contort- 
ed strata of many colors, nowhere toned down or overshadowed 
by vegetation, and standing out in the dry crystal atmosphere of 
the desert. 
In the northern part of the range, a few miles before it sinks 
into the plain of Debbet-el-Ramleh, the granite dips under the 
sandstone, and one can step from one to the other. Almost at 
the northernmost peak of the Sinai range, several hundred feet 
above the level of the road through the wadi which leads from 
the foot of Surabit-el-Kadim to Debbet-er-Ramleh, there are 
some horizontal strata of limestone over the sandstone. The 
sharp definition of these strata, seen in their elevated position, 
is one of the most interesting geological features of the peninsula. 
They are the last plates of the limestone of Sinai which has sur- 
vived the long process of denudation that has uncovered the 
sandstone and the igneous rocks of the southern portion of the 
peninsula. 
The sandstone rocks of northern Sinai dip under the shifting 
sand at the southern edge of Debbet-er-Ramleh. 
The plain of Debbet-er-Ramleh is a strip of sandy desert about 
ten miles wide, connecting the heads of the two gulfs of the Red 
Sea. It is not straight but V-shaped, with its angle to the 
southward. Into the angle formed by its two sides projects the 
gigantic escarpment of the plateau of the Tih, which rises almost 
perpendicularly several hundred feet above the plain. ‘This 
plateau is the continuation of the limestone strata of which we 
noted the traces on the other side of the plain overlying the 
sandstone. ‘The sandstone does not re-appear in our progress 
northward until we reach Lebanon, and the granite and por- 
phyry do not crop out again until we strike the chain of Cassius,. 
nearly 400 miles away. 
