20 Part I. Chapter ı. 
so as to strike the headwaters of the Columbia, which they descended to the 
Pacific Ocean. In March 1806, they started eastward to retrace their steps. 
Early in July, the leaders separated for a time, Clark descending the Yellow- 
stone and Lewis the Missouri, until they met at the junction of the two 
rivers and in September reached St. Louis, where they forwarded to JEFFERSON 
an account of what they had done. They had opened the great West to science 
and trade. — About this time DAavıD THOMPSON, an astronomer and surveyor, 
in 1796 was sent by the North West Company to explore the source of the 
Mississippi. He visited the Mandan villages by way of Rainy Lake, lakes 
Manitoba and Winnipeg, Saskatchewan and Assiniboin rivers returning by way 
of the Red River of the North, Lake Superior and St. Louis River. On another 
expedition in 1806 he discovered the upper waters of the Columbia River, and 
was’ at Lake Athabasca in 1810. SIMON FRASER also figured in the exploration 
of the great Northwest. | 
While Lewis and Clark were descending the Columbia, another army officer 
was conducting explorations which were scarcely less important than theirs. 
In 1805 ZEBULON PIKE turned his face towards the headwaters of the Missis- 
sippi River. The winter was spent in what is now Minnesota. In his search 
for the source of the Mississippi, Pike penetrated a lake-dotted region and 
explored the Leech Lake drainage system. Returning to St. Louis, he started 
for the Southwest. He crossed the great plains to the Arkansas River and 
then up that river, where WILKINSON and three other men left the party and 
returned down to the river to the settled country. The others struck westward 
across the mountains reaching in November the bold peak which was after- 
ward named in the leader’s honor. They finally reached after much privation 
and hardship the Rio Grande River. PiKE was made prisoner by the Spaniards 
at Santa Fe and after release was sent home by a round about route throug 
Chihuahua and Texas, and so \ended the second great transcontinental eX- 
pedition. Others followed in rapid succession. Those in which botany was 
given a prominence must now be mentioned. 
THoMmas NUTTALL, an Englishman, long resident in Philadelphia, accom- 
panied by BRADBURY left St. Louis in 1809, crossed the Kansas and Platte 
rivers and ascended the Missouri River, returning enriched with much material. 
Leaving Philadelphia again in 1818, NUTTALL reached the mouth of the Ar- 
kansas River and botanized extensively in the region returning with large 
collections which formed the basis for his book a Journal of Travels into the 
Arkansas Territory during the year 1819, Philadelphia 1821. In 1819 Major 
STEPHEN H. LONG was deputed by President MONROE to discover, if possible 
the South Pass, and on his return make an attempt to determine the sources 
of the Red River. Proceeding up the Missouri and its South Fork, they 
reached the mountains where the lofty mountain (Long's Peak) was discovered, 
the party returning homeward via, the Arkansas River. The results of the ex- 
pedition led by Governor Cass appeared in Silliman’s Journal in ı822 by JOHN 
TORREY. The plants collected by Tmomas Say in Long’s second expedition 
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