There are three great museums at South Kensington - the Natural History Museum, the Science Museum and the V&A. But there used to be a fourth, indeed there still is, except it's been entirely swallowed up by one of the big three. The Geological Museum started out on Jermyn Street in 1835, then known as The Museum of Practical Geology, and was essentially a collection of rocks. A century later it had outgrown its premises so looked to move on to Albertopolis (the original site became the flagship store of Simpsons menswear, now Waterstones on Piccadilly). In 1935 the museum moved into a new building on Exhibition Road squeezed inbetween the Science Museum and Natural History Museum, on land earmarked for an extension of the latter. Only in 1973 was a physical public connection created between the Geological Museum and Natural History Museum, with a full merger of the two bodies taking place in 1986.
Which means most people visiting the Natural History Museum think of it as a place devoted to animals and maybe plants, but probably not rocks. Indeed if you enter via the main hall where the diplodocus lingers, you might never find your way to the geological bit at all. It's off to the right on the ground floor past the fossils and creepy crawlies, then you have to think to walk all the way past the stuffed birds and there's geology, now rebranded as the 'Red Zone'. Alternatively if you come in direct from Exhibition Road you walk straight in, because that was the original entrance to the Geological Museum (top tip, on busy days it has a much shorter queue), and then your first experience of the NHM is earth science rather than dinosaurs.
Visitors to this part of the museum didn't usually make it up as far as the top galleries, so in 1996 a single escalator was added to try to lure folk up to the second floor. It's almost irresistible. Rising up through the middle of the main atrium it passes between a backdrop overpainted with constellations and through the raging core of the Earth. Obviously it's not the real Earth, merely a globe constructed from thin sheets of bashed metal, and those aren't incandescent flames, merely a bit of red lighting. But it's effective enough, and it serves its purpose to deliver you to the volcano and earthquake bits upstairs.
Everybody likes the volcano and earthquake bits, because they're a reminder of our planet's immense capability to transform and kill. A series of displays, some with buttons to press, allow you to explore where the world's most active volcanoes are and the many different forms they take. If the lava doesn't get you then the burning gases might, and if they pass you by then the ash cloud could still spread round the world and drag the temperature down, so be warned. A theme which shines through is how magnitude and rarity are connected, so if the panel on supervolcanoes scares you, be reassured that none has erupted since humanity began. As for earthquakes the display is right up to date with footage of the Japanese tsunami, but what every visitor wants to do is stand in the Kobe supermarket simulator (circa 1995) and be shaken for 20 seconds, as meekly as health and safety will allow.
On the opposite side of the top floor we get Restless Surface, which is an attempt to make weathering and erosion sound exciting. It almost succeeds, with frozen lightning pierced through sand and a giant stalagmite hewn in two, but I expect most kids rush through until they find a tray they can drip water into (to show how river deltas and meanders are formed). They might not linger long either through From The Beginning, a timeline of the evolving Earth spread along the entire length of the building. But I rather enjoyed the dark and dated scientific presentation, fact-dense with graphs and maps, as well as with fossils from the relevant time period. And I learnt plenty too, not least the (to me) surprising fact that Scotland and the Lake District used to be on separate continents across a long-gone ocean until 425 million years ago.
If you like shiny things you'll enjoy Earth's Treasury, which is where the museum finally gets to focus on rocks. Almost everything that makes up the Earth's crust gets a look in, from ubiquitous silica and granite to rare ores and precious stones. The Geological Museum has been gifted several special collections of gems over the years, and these are prominently displayed along with a long sequence of mineral-by-mineral displays. So yes, there's a cabinet of rubies and opals, but also a look at coal and slate, and quartzite and mica, in all their many and magnificent forms. What's intriguing is the significant overlap with another much-loved corner of the Natural History Museum, the Minerals gallery, with its magnificently cabinetted 1881 presentation. That's off-limits at the moment, incidentally, but should reopen by the end of next month once transformation of the main hall's upper balcony is complete.
Once back at ground level in the Red Zone, will you head for the cafe or will you head for the gift shop? The latter is more interesting, not least because it doesn't take up the full length and hides a further gallery on Human Evolution at its rear. Of the eight different species of hominins how come we became dominant, and so recently? And there is one more room you should poke your nose into, which is the London Information office of the British Geological Survey. This is proper old school science, with a study zone and helpdesk, plus a fantastically comprehensive array of publications for purchase. Geological maps and guides to every tiny area of Britain fill one wall, plus some slightly less academic sheets and guides and postcards, and some rocks. "This is my favourite bit," said a man leading his unwilling 5 and 8 year-olds through its portal, "but then I am a geologist".
And after all this there's still the rest of the Natural History Museum to explore, including the dinosaurs and the blue whale and the new-ish experimental wing, to make a proper day of it. And conversely, if you ever turn up and the main building is packed out with families and/or tourists and/or schoolchildren, be reassured there's probably an interesting bit round the back that isn't.