Dr. Peal has reached conclusions which present an imaginary picture of the interior structure of the great geysers of the Park, that bears a striking resemblance to what the two caves of the Black Hills prove to be the true conditions; although it is evident he had in mind caverns of no such vast extent, nor of so complicated a system of cavities and tubes. He overlooked an important feature, however, in not accepting Professor Comstock's idea of the tube having a double curve. The double curve is, or was, conspicuous in both the caves. Unfortunately, its perfection in Wind Cave was necessarily partially sacrificed to make the passage traversable for visitors; but in describing the enormous labor of opening up the cave, Mr. McDonald showed how an arching "crawl" had been worked down by blasting, and the depression beyond filled to raise it to the desired level for securing the present easy passage at the bottom of the main tube, which is the entrance passage. This double curve in the tube is simply the rough original of the S trap of sanitary plumbing. In both caves it is somewhat irregular and deformed, but the familiar "trap" is easily recognized. The destruction of one of the Yellowstone geysers was, no doubt, due to the breaking of the S. One of the many reasons for establishing military control over the Park is said to have been the disastrous results following the introduction of a large quantity of soap into the geyser to cause a premature eruption. The impatience of the party was rewarded by an eruption accompanied by explosions that shook the earth for a great distance, and the geyser has not been seen in action since. Dr. Peal finds the theories advanced for the generation of steam unsatisfactory and insufficient, especially in the class of geysers having a long steam period. He says: (page 423)