left of them, was fully appreciated, it became evident that the granite axis so characteristic of mountains was not necessarily pushed up from beneath and protruded through the parted strata, but was in many cases only a sub-mountain core of igneous matter slowly cooled into granite and exposed by subsequent erosion greatest along the crest. Next, attention was drawn to the enormous thickness of the strata involved in the folded structure of mountains. From this it became evident that the places of mountains before they were formed were marginal sea bottoms off the coasts of continents, and receiving the whole washings of the continents. Thus the steps of the process of mountain formation were (1) accumulation of sediments on offshore sea bottoms until by _pari passu_ subsidence an enormous thickness was attained. This is the _preparation_. (2) A yielding along these lines to the increasing lateral pressure with folding and bulging of the strata along the line of yielding, until the mountain emerges above the ocean and is added to the land as a coast range. This is mountain _birth_. (3) As soon as it appears above the water it is attacked by erosive agents. At first the rising by continuance of the crushing and bulging is in excess of the erosion, and the mountain grows. This is mountain _youth_. (4) Then supply and waste balance one another, and we have mountain _maturity_. (5) Then the erosive waste exceeds the growth by up-bulging, and mountain _decay_ begins. (6) Finally, the erosive forces triumph and the mountain is clean swept away, leaving only the complexly folded rocks of enormous thickness to mark the place of a former mountain. This is mountain _death_. Such briefly is the life history of a mountain range. In all this we have said nothing about causes. In this connection there are two points of especial importance: (1) Why does the yielding to lateral pressure take place along lines of thick sediments? (2) What is the cause of the lateral pressure?