154 . GEOLOGICAL SURVEY OF THE TEERITOEIES. 



CHAPTER IV. 



THE MIDDLE PARK. 



In Chapter I was given a brief description of the principal topo- 

 graphical characters of that region, the drainage system of which, as a 

 whole, may be considered as composing the Middle Park. The general 

 symmetry of this drainage, with Grand River as an axis, its radiating 

 tributaries, as well as the remarkable isolated character or unity of the 

 system, all of its waters finding their exit through the single outlet — 

 caiion of the Grand — were there noticed, and attention called to the 

 fact that, notwithstanding the great basin-like character of this area, as 

 indicated by these features, yet this character is in great part lost by 

 the prominence of many of the ridges separating its secondary drainages, 

 and the general diversity of much of its surface, wherein it presents a 

 striking contrast with the far-better defined basin-like character of the 

 IsTorth and South Parks on either hand. The fact that this isolated and 

 independent system is the easternm.ost region in the United States, in 

 which Pacific waters take their rise, was also referred to, while it was 

 suggested that, as a geological basin, the northern side is wanting. 

 The general course of the streams forming the system, as well as the 

 more salient features of their valleys and separating ridges, were also 

 briefly sketched out. 



The distribution and structure of the rocks forming this region will 

 now demand our attention. (See map at front of chapter. Fig. 8.) 



All the eastern, southern, and western rim of this isolated drainage 

 basin, as well as the massive mountain areas bordering much of the 

 same, chiefly on the east and south, are composed of apparently the 

 same system of metamorphic crystalline schists and granites that are 

 found on the east slope of the range, excepting always certain smaller 

 areas of Paleozoic sedimentary rocks, which occur near the sources of 

 the Blue River, and which are quite separated from the younger sedi- 

 mentary rocks to follow, and will not be further considered in this report. 



All the northern and middle portions of the park, which include all 

 the lower and more truly park-like portions, are composed, excepting a 

 few areas of Archsean rocks along the Grand, of younger sedimentary 

 rocks, which are not, as a rule, greatly disturbed. 



THE CRETACEOUS FORMATION OF THE MIDDLE PARK. 



Apparently the oldest of this series, resting, where found, directly 

 upon the crystalline rocks, is the Cretaceous. This formation seems to 

 vary from about 3,500 to about 4,500 feet in thickness, and is divided 

 much like the Cretaceous upon the east side of the range, with some 

 very strong lithological resemblances existing between some of the divis- 

 ions. 



At the base is a series of sandstones, some of which are red, and both 

 massive and shaly, but the most characteristic feature of the group 

 is the presence of hard, whitish or white, highly siliceous sandstones, 

 often conglomerates, which, at times, form such compact quartzites that 

 in hard specimens the rock can hardly be distinguished from some ar- 

 chasan quartzites. Being so hard, erosion has generally molded these 

 sandstones into prominent exposures, leaving the softer beds "in less no- 

 ticeable positions, while their marked persistent lithological characters 



