| Summary: | 8 II I S TO II f OF GRAND FORKS COUNTY In the western part of the county the uplands consist almost bodily of alternating beds of blue clay and soft shales. Collectively, these Cretaceous strata are about one thousand feet in thickness. The deptli of the overlying drift varies from merely nothing on the tops of the higher eminences to twenty or more feet in places on lower ground, but usually in tbe uplands the glacial drift amounts to only a few feet of bowlder clay, with many scattered bowlders at or near the surface. On the valley slope tbe drift has a greater thickness than in lire hill district of the county. The bowlders are of all sizes up to those ofthiee to five feet in diameter, but in more rare cases a tew are reported as being ten or twelve feet in diameter. They are usually of granite and associated rocks, with occasionally one of limestone. Some of sandstone occur here, but they are very rare. The "hardheads" came from the Laurentian axis of the continent around Hudson bay, and the limestone bowlders are from the region around Lake Winnipeg. The Cretaceous formation of the upland country was not only once continuous across the entire valley, but also was originally 500 or more feet higher, as much as that amount having been denuded from the surface prior to the Glacial period. Tlie hollowing out of tlie valley itself dates from about tbe close of Pliocene times and was completed essentially the same as it is now, some minor rough surface features and a deeper basin, excepted, when the Ice age began. The great width.of the vn.le.y is due to the easily erosible nature of tlie strata in which it was excavated by rain and stream erosion. Two of tiie land belts running through the county consist of sedimentary deposits more recent than the bowlder clay. The oldest of the two in relativeage is the tract called the Elk Valley. This is a delta deposit of sand and clay silt, formed by a temporary glacial river that came down from the Golden valley of Walsh county. This ice-born torrent flowed within a great rift ol the icesheet, the part of the rift now represented by the delta then forming an estuary-like inlet to the glacial Lake Agassiz. 'The lake then filled the lied River Valley as far north as Grand Forks county, and was in process of lengthening northward to the country around Lake Winnipeg. The icesheet was probably about a half mile in thickness in the valley and during tlie epoch of the lake the ice margin was receding. The sediments of tlie delta extend from around McCanna to the vicinity of Mayville and Portland and also include some of the ridgy land along its eastern border. The average thickness of this sedimentary belt is about, forty feet and Upham estimates its bulk at from 1,} to 2 cubic miles. Its lower part is so saturated with water as to form a quicksand, which is reached in wells from 12 to 24 feet in depth, anil furnishes an abundant supply of very pure water. Scanned with a Zeutschel Zeta book scanner at 300 dpi. Edited with Multi-Page TIFF Editor.
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