began to perceive the feeling that had stirred the ponies to resist when turned toward the silent plains that lay spread for mile upon mile before them.

After a few minutes Stacy's pony scrambled to its feet. The lad was in the saddle in a twinkling.

"Now, I guess you'll go where I want you to. Whoa! Quit that b-b-b-b-bucking."

The animal had gone into a series of jolting bucks, with back arched and head well down. The fat boy held his seat well. His face was red and streaked with perspiration which ran down it in tiny rivulets under the violent exercise to which he had just been subjected.

The boys forgot the serious side of the incident in their enjoyment of their companion's discomfiture.

Tom Parry gazed upon the scene with more than ordinary curiosity. It was the first opportunity he had had of observing a Pony Rider Boy in action. At that moment Stacy Brown was most distinctly in action. Most of the time there was a broad patch of daylight under him, and when he hit the saddle it was with a jolt that seemed as if it must jar his head from his body.

"Put some salt on his tail," suggested Ned Rector.

"Y-y-y-you do it," gasped Chunky, which brought a roar of laughter from the whole party.

"Yes, why don't you?" teased Tad. "It's the only way you can make good."

"Salting down horse is not my business," laughed Ned.

All at once the pony whirled, heading down the mountain side with a disconcerting rush that nearly brought disaster upon its rider.

With a shout the rest of the boys urged their mounts into a jog-trot and followed on down the trail as fast as they dared, for the descent was steep and dangerous.

"He'll break his neck!" cried the Professor.

"After that bucking I'm sure Chunky's neck is too well fastened to come off," laughed Tad.

Stacy was out of sight. They could hear him yelling at his broncho, so they knew he was still in the saddle and right side up. The other ponies, apparently having forgotten their fear, were following the leader willingly now.

All at once they saw lad and mount burst into view on the plain below.

"He's on the desert!" shouted Tad.

Laughing and shouting words of encouragement to the fat boy, the Pony Riders hastened to the base of the hill. Stacy Brown was still busily engaged trying to subdue his pony, though some of the lads shrewdly suspected that their companion was urging the animal on in order to show off his horsemanship.

In a moment more they, too, were in difficulties. No sooner had their bronchos set foot on the desert than a sudden panic once more possessed them. Professor Zepplin's pony whirled on its haunches, then began climbing the rocks, with the agility of a squirrel.

The others, however, had troubles of their own, which saved the Professor from being laughed at. The animals seemed determined not to be forced to go on, and it required severe measures to induce them to take up the desert trail. Tom Parry's mount did not exhibit the same fear as did the others. Still, it gave him more or less trouble, appearing to be excited, in spite of itself, by the actions of its companions.

At last they succeeded in lining the animals up in an orderly formation. Their next move was to get the burros moving along ahead of them. The way being open and level there was no necessity for leading the pack animals now. These could take care of themselves without danger to the outfit.

"And this is the desert!" marveled the Professor.

"It is," smiled the guide.

"Looks to me more like a landscape of German measles," averred Stacy, as they moved along through scattering sage brush and open sandy stretches.

Now that they had reached the plain itself, they discovered that it was not one level stretch of land. Instead, the country was rolling; here and there were wide reaches of whitish desert sands and alkali sinks. The atmosphere was like an oven. Not a breath of air was stirring. Already the lads were mopping their brows and fanning their faces with their sombreros, while spots of dark shining moisture on the ponies' sides bore evidence that they, too, felt the baking heat.

"I say, fellows, let's find some shade," called Stacy.

"All right, go ahead and we'll follow," laughed Tad.

"I'll ride up to the top of that knoll and make an observation."

Tom Parry smiled appreciatively as the lad galloped up the sharp rise of ground, where Chunky sat on his pony, shading his eyes as he gazed off over the cheerless desert.

"Well, how about that shade?" shouted Ned.

Stacy turned disconsolately and rode back to his companions.

"There isn't any," he said.

"Of course not," laughed Ned.

"But I know how to make some," added the fat boy.

Slipping from his pony he cut some sage brush, which he fashioned about his head in the shape of a hood, so that it gave his perspiring face some protection from the intense glare of the sun.

"Now, all you need is a strip of mosquito netting," suggested Walter.

"And a little red rocking chair," added Ned.

"With a dish of ice cream," laughed Tad.

"I guess you will have to be satisfied with a cup of alkali water," interjected the Professor, dryly.

"You will find the air much cooler, shortly," the guide advised them. "The sun is going down now and I think we had better make camp, if the Professor has no objections."

"Not in the least. In fact, I am quite ready to call it a day's work."

"Where do we camp, Mr. Parry?" asked Tad.

"Right here. It is as good a place as any that we shall find. There is little choice out here."

They were now in a broad valley, the rolling hills covered with a sparse growth of sage brush rising gradually on each side.

The boys threw themselves from their ponies gladly, stripping the saddles from the animals' backs.

"Better stake the animals down, for the first two or three nights, so they won't take French leave," advised the guide.

"How about the burros?" asked Tad.

"Let them roam. They'll stay as long as the ponies are here. The pack animals will fill up on sage, after which they will come back to camp to sleep."

All hands began to unpack. The tents were pitched in record time, cots unfolded and preparations for the night made with a skill that comes from long practice in the open.

"What are we to do for a camp-fire?" asked Walter. "There is not a single stick of wood about here."

"Burn the sage," answered the guide.

"That stuff won't burn," retorted Ned.

"Try it."

They did. In an incredibly short time a hot fire was blazing up, on which they piled armfuls of the stunted desert growth.

"Now, get your food ready and I will cook it," said Parry, as the flames began to die down.

When the fire had settled to a bed of hot ashes Tom thrust the bacon directly into the ashes, placing the coffee pot near the center, around and on top of which he heaped the ashes. It was a new method of preparing a meal, and the lads watched the process with keen interest.

"I shouldn't think that bacon would be fit to eat. However, I presume you know what you are doing," said the Professor.

"It's the only way, sir," replied Parry. "We have to work with the implements that nature has provided."

"Nature must have been in a stingy mood when she made this country," laughed Ned.

"I don't agree with you," said Tad. "It is the most beautiful and interesting scene that I have ever looked upon."

Parry nodded approvingly.

"And as fickle as it is beautiful," added the guide. "The supper will be ready by the time you have the table set, boys."

In spite of the heat the lads realized all at once that their appetites had not suffered. Bacon, jelly and biscuits, which had been warmed over the ashes, seemed to them to have reached the proportions of a banquet.

Stacy helped himself to a large slice of bacon which he proceeded to munch. No sooner had he begun, however, than he made a