PHYSIOGRAPHIC AND GEOLOGIC DEVELOPMENT 239 



miles away at Pongo de Mainique. The mashing and crumpling 

 that the schists have experienced at Puquiura is so intense, that 

 were they a part of the Silurian series the latter should exhibit 

 at -least a slight unconformity in relation to the Carboniferous 

 limestones deposited upon them. 



If our interpretation of the relation of the schists to the slates 

 and shales be correct, we should have a mountain-making period 

 introduced in pre-Silurian time, affecting the accumulated sedi- 

 ments and bringing about their metamorphism and crumpling on 

 a large scale. From the mountains and uplands thus created on 

 the schists, sediments were washed into adjacent waters and ac- 

 cumulated as even-bedded and extensive sheets of sands and muds 

 (the present slates, shales, quartzites, etc.). Nowhere do the sedi- 

 ments of the slate series show a conglomeratic phase; they are 

 remarkably well-sorted and consist of material disposed with 

 great regularity. Though they are coarsest at the bottom the 

 lower beds do not show cross-bedding, ripple marking, or other 

 signs of shallow-water conditions. Toward the upper part of the 

 series these features, especially the ripple-marking, make their 

 appearance. During the deposition of the last third of the series, 

 and again just before the deposition of the limestone, the beds 

 took on a predominantly arenaceous character associated with 

 ripple marks and cross-bedding characteristic of shallow-water 

 deposits. 



In the persistence of arenaceous sediments throughout the 

 series and the distribution of the ripple marks through the upper 

 third of the beds, we have a clear indication that the degree of 

 shallowness was sufficient to bring the bottom on which the sedi- 

 ments accumulated into the zone of current action and possibly 

 wave action. It is also worth considering whether the currents 

 involved were not of similar origin to those now a part of the 

 great counter-clockwise movements in the southern seas. If so, 

 their action would be peculiarly effective in the wide distribution 

 of the sediment derived from a land mass on the eastern edge of 

 a continental coast, since they would spread out the material to 

 a greater and greater degree as they flowed into more southerly 



