Náttúrufræðingurinn - 1955, Side 64

170
NÁTTÚRUFRÆÐINGURINN
örvar, sem kortið sýnir suðaustur af Hvítárvatni. Þegar ég athugaði
rákastefnu þar fyrsta sinni (8. sept. 1941), þótti mér svo sjálfsagt,
að hún væri af Langjökli, en ekki á Langjökul, að ég rannsakaði ekki
sem skyldi, hvort heldur var. En nú, þegar ég hef athugað ráka-
stefnuna betur austar, hef ég grun um, að þarna hafi mér skjátlazt.
Því má vera, að þessar örvar bendi í öfuga átt. Nánari rannsókn verður
að skera úr þvi.
Af hinni suðrænu og suðaustrænu rákastefnu á ofanverðu vatnasviði
Þjórsár má ráða, að ísaldarjökulinn hefur fyrr tekið upp af vatna-
skilum á Sprengisandi og Kili en af hálendinu þar fyrir sunnan. Snæ-
lína hefur þá legið mun hærra en þessi vatnaskil, meðan enn var
óbráðinn þykkur jökulskjöldur yfir lægra landsvæði á öræfunum
sunnan þeirra. Sá jökull var síðasta leif eiginlegs ísaldarjökuls hér á
landi. Ætla má, að þar hafi hann verið þykkastur og því hjarað
lengst.
SUMMARY
Studies on glacial striæ in Iceland
by GUÐMUNDUR KJARTANSSON
The author has studied the glacial striæ in many places in Iceland, especially in
the area shown on the map, fig. .3. In previous publications he has pointed out a
considerable shift in the directions of the ice movement during the thinning out and
retreat of the ice of the last glaciation in Árnessýsla, S. W. Iceland (see quota-
tion in foot note). The later ice movement obliterated the striæ of the previous
one in most places, except near the front where the later movement was of short
duration and where two sets of intersecting striæ are found. Hence, the preserved
striæ in general must belong to a late stage of the last retreat of the ice. Only
those found on promontories or on high mountains could be assumed to have
originated from the maximum stage of the last glaciation.
Thus the striæ pointing from E. to W. on the northwestern tip of the Reykjanes
Peninsula may be due to the maximum stage. They show that a vaste ice stream
moving out of Faxaflói reached the mouth of this bay. Another set of striæ de-
scending from the interior of the peninsula indicate a later stage, when the great
glacier of the bay had retreated and an ice divided was formed along the
peninsula.
The upper limit of striation on mountain sides has been searched for in many
places to determine the thickness of the ice sheet covering the land below. Thus
I have come to the following results.
Striæ on Fjarðarheiði, a pass in the mountain chain of Austfirðir (E. Iceland),
show a thickness of the ice of 660 metres on the western side of the pass, in the
valley of Fljótsdalshérað. — In Lónsheiði and Hvaldalur (S. E. Iceland) a thick-