Our big job was to map the laccoliths near Deadwood. A laccolith, or rock cistern, is a lava body which in very ancient times squirted into the cracks of the strata. The lava had penetrated between the strata of the northern cover of the Black Hills, swelled to lenses between the strata; and, particularly, it selected and penetrated the soft shale beds which grow thicker and more numerous upward among the formations. Thus after erosion of the present landscape, both large and small lava lenses were revealed as resistant hills, the largest toward the bottom of the pile of strata and the smallest and steepest toward the top in thick, black ancient mud deposits.
Mostly, the laccoliths were injections of volcanic fluid up a crack, which met a hard bed and bent to squeeze the paste or lava into a soft layer. The result was an underground lava flow which ruptured the beds. Apparently the first rush brought up fragments of the rocks below. This fragmentary stuff of mud and gravel was overridden by the lava, until the latter penetrated horizontally a mile or two between strata, arched the layers above, and solidified at the Devil’s Tower with vertical columns like the Giant’s Causeway in Ireland.
This group of subterranean volcanic eruptions between strata probably came under sea bottom at the same time that the Yellowstone upland began its open-air outpourings farther west. But in the Black Hills there is no sign the laccolith lavas ever broke up to the top country.
The Black Hills, like the Rocky Mountains, were a long time rising in waves of action, whereas the lava intrusion was a relatively short episode of one of the latest of these spasms. However, that episode entails a long story of numerous injections. It takes us down into crust and along through the millennia.
Always think in millions of years. It is wise also to think in millions of miles and to remember that the sun and the Milky Way are parts of the same system as the earth. And remember that a ledge or a boulder doesn’t worry about living 20 million or 100 million years. A skull is a boulder. That old brontotherium rhinoceros with a forked horn, standing eight feet high and fifteen feet long, lived in the upper Oligocene, when clay and volcanic ash were being deposited in the Bad Lands of South Dakota. Probably vast flood plains of rivers were his habitat, swamp reeds and leaves were his food, and floods washed his bones and buried his skull where we find them today. The country of open glades was probably like the safari land of central Africa.
Brontotherium’s skull in Chicago Natural History Museum dates from about 30 million years ago. The bones are scattered, and few complete skeletons have been found. Man’s ancestor may have started 10 million years ago, but the nearest approach to an ape who lived in the trees of old Bronto’s forests was an opossum. Furthermore, nothing like flint tools have been found in the rhino strata. The apes started in Europe and Asia in the next geologic period, and some fossilized monkeys have been found in South America. But men and monkeys are too soft. They don’t make good fossils.
The bones we found were of turtles, in clays upheaved on the top of the Black Hills uplift. These clays were afterwards eroded into the present valleys, and probably were contemporaneous with the riverbed silts, where the rhinoceros skulls were found. So our turtles and rhinos were no doubt neighbors in 29,998,000 B.C.
Our sojourn in the Black Hills was not without adventure. One evening when Boutwell and I were riding home to Deadwood, I dismounted and jumped into the shrubs of a gully to knock a rock specimen off a ledge. From beneath my feet came a buz-z-z like a swarm of bees. I had jumped right on a rattlesnake and could feel his coils against my ankle, and no leggings that day. Boutwell called out, “Oh let me see him! I’ve never seen a rattlesnake.” I made a suitable reply and, somehow, leapt clear before the snake had a chance to strike.
Another adventure concerned my gold watch, a gift from my dad on my twenty-first birthday. I lost it from a chain which broke against the saddle pommel at some dismounting point. I advertised for it by placards at railway stations and, amazingly, it was returned. A Salvation Army man found the watch, badly trampled by my horse, at a back country place, brought it to me in Deadwood, and received the reward. I took it to the maker in Waltham, where it was restored; and I am wearing it fifty-four years later, converted from a hunting case to a stemwinder.
John Irving of Yale, whose father had been a mining geologist in the Great Lakes district, was one of the most lovable companions I ever camped and tramped with. We were together in the Black Hills, where we hired a wagon outfit to cross the Hills to the Devil’s Tower. The personnel was a masterpiece of improvisation. The cook was a fat boy who told marvellous tales of adventures. Among other things, he had been a human ostrich in the circus, and he assured us that chewing up glass and swallowing it did no harm if you knew how. So elaborate was his cooking that again and again we ran out of grub. Furthermore, meals were generally late, but we knew better than to hurry the supper and his finishing touches. When finally a meal was ready, he advanced to our tent, bowed, and called out, “Gentlemen, you will now proceed to sagastuate.”