Here is my attempt at a competitive mid-range deck made from the best stuff in Earth! I like this deck enough that I took the time to update the primer to be much more thorough and cover every one of my card choices. Let's burrow in:

Avatar (Geomancer):

Yes, Sorcerer is still the best avatar for straight up card advantage. It's also fantastically boring. Geomancer lends card advantage in the form of not having to spend a draw step drawing a site for the first several turns, and possibly never depending on the circumstances which I will cover later. It also has greater resilience against the terribly-unfun-to-play-against site destruction decks made possible by Arthurian Legends. It also means that you can make the most of your own Roots+Sinkhole (or Craterize) board reset combo to work in your favor by being able to recover quickly with Geomancer's signature ability.

Artifacts:

Onyx Core remains an inclusion that is welcome more often than not. The benefits of drawing it early are obvious, but even late game it can be held in reserve to assist recovery if you have to detonate Roots somehow and got unlucky enough to draw 0-1 Bedrocks, or if you somehow managed to get squeezed out of not having quite enough mana to summon your big minions.

Auras and Magic:

Crusade is an obvious inclusion for just about any mono-Earth deck. Ideally you want it early and placed on your opponent's side of the board for maximum aggression. Drawing it later is good too if you can get it just in time to start summoning your big minions right to the enemy avatar provided they're not also taking shelter inside a Gnome Hollows or something else you can't enter. In those situations, Midland Army's tap ability comes in handy, as does Craterize, or even Stone Rain if they're at DD.

Entangle Terrain serves as some added insurance against aggro decks, buying time enough for you to stabilize the board with something like Earthquake and/or Orb. It can be fetched with Common Sense for whenever you need extra time to swing the board state in your favor if you're falling behind.

Divine Healing is more insurance against aggro and otherwise bad starts or situations where you fall behind too quickly in life total. In late game, it synergizes well with Craterize, letting you be a little more reckless with its use knowing you can recover from the damage quickly.

Tithe can potentially extend the time you have to keep drawing spells instead of sites for each of your turns. It also has some synergy with Stone Rain, making an otherwise over-priced damage spell do some respectable work. Casting it early also gives you greater selection of which sites you get to place in a deck that doesn't play Crossroads. Lastly, it serves as a cheap way to fetch a site for pitching to Craterize if you don't want to tap your avatar or use a draw step to get one.

Common Sense has a grand total of twelve targets in this deck. I find it's worth having a full play set in a mid-range deck like this because it gives me a much better chance to fetch what I need for most situations, which is crucial for this type of build. It's very rarely a dead draw and its low casting cost makes it incredibly easy to double-spell in the mid- and late-game, especially for a deck that has such consistent access to plentiful mana.

Dispel is most often a Common Sense target for when you need to get rid of a particularly troublesome aura or artifact, or to stop an Enchantress or Battlemage from running you over. It has so many relevant targets that it's definitely worth a single copy in the main deck.

Border Militia is a versatile little ordinary that can provide you with some cheap fodder for slowing down enemy aggression, or overwhelm the board later when combined with Orb and/or King of the Realm. Just be careful if you choose to use it against Battlemage because they can easily turn it into a lot of card advantage if they manage to find a timely Screaming Skull.

Bury is a cheap, staple removal spell that can be fetched with Common Sense and only tends to be bad against Water decks. Don't forget that it can be used to burrow artifacts and potentially deprive your opponent of their benefits if they don't have a burrowing minion to retrieve them.

Rescue is another Common Sense target with a lot of situational usefulness. Lady Iseult and King of the Realm are excellent minions that are sadly easy to kill, so being able to fetch Rescue on demand can help maintain a favorable board state with them. It can also be copied with Orb, potentially with devastating effects if you get back a deceased pairing of Wraetannis Titan and/or Atlas Wanderers.

Cave-in is similar in utility to Bury, but has more potential to punish over-committed opponents at the cost of one more mana and not being a Common Sense target. Using it with Orb can dramatically swing the board state in your favor at half the cost of Craterize and a bit more precision than Earthquake.

Gigantism is an infrequent but always welcome spell with its ability to turn even a lowly foot soldier into a serious threat for a single turn. You only get one use of this and you can't count on being able to copy it with Orb in most games, so use it wisely and hold onto it for an opportunity to deal some fine gourmet damage as the situation dictates.

Earthquake is a game-changer more often than not for its ability to kill multiple minions at a reasonable cost and switch sites around to make them more vulnerable to attack in the absence of Crusade. It's naturally less effective against decks with a lot of water sites, but you can still move things around to open them up to more advantageous angles of attack, potentially breaking up bodies of water to strand dangerous enemies like Mester Stoor Worm and Giant Shark if only temporarily.

Minions:

Frontier Settlers can give you some quality ramp in the form of an extra site on turn three. They can also be used in tandem with Crusade and/or Rift Valley to expand the aggressive placement of your own sites and keep the pressure up on your opponent's side of the board. After they've done their primary job, they can serve as cheap fodder against enemy minions or apply pressure to the enemy avatar depending on where they end up on the board.

Lady Iseult is the classiest dame on your side of the board and does a fine job of maintaining your board presence in most situations. She can allow you to be a bit more aggressive even with your smaller minions given that they come right back to your hand if they die. She is unfortunately rather easy to kill due to being low-power and needing to be nearby the front lines, so try holding a Rescue in order to keep her around longer. She can also benefit from the protection of sites like Gnome Hollows, Free City, and Impenetrable Copse depending on the situation, so placing those sites forward is ideal in an Iseult game. She may or may not need to move around a lot, but placing her near your Stone-Gaze Gorgons is sometimes an option for keeping her out of reach of enemy minions, and she makes a good bearer for Scarecrow if you're facing some airborne threats.

Autumn Unicorn is a solid early minion that contends well with most other minions of its cost. Simple and effective, it'll help keep you from falling behind on board too early especially when supported by the more expendable foot soldiers.

Crown Prince is another early minion that holds the line and synergizes well with some of the other cards. Having a foot soldier in reserve can keep him around for a long time and allow him to survive Earthquake and Craterize. He performs well early on under a Crusade and even later with King of the Realm sitting somewhere relatively safe.

Root Spider is another high-utility beasty with a lot of value for its low cost. It can single-handedly shut off avenues of attack from non-burrowing minions and save you from an early onslaught when used correctly with other defensive cards like Free City. It can also be used aggressively, pushing forward and disabling defenders while you gain more ground towards overwhelming your opponent's side of the board. Of course, its use is rather limited against Water decks, but it can still perform respectably if used with a well-placed Bedrock which can't be flooded.

King of the Realm makes all mortals yours to command and strong enough to close out games with the help of Border Militia and/or Crusade. He only gets thwarted by King Arthur or another King of the Realm played after, so keep removal handy if you anticipate your opponent playing these cards. He is generally more valuable staying safely in the back row or ideally nearby wherever Lady Iseult happens to be.

Midland Army is an even bigger, nastier beater that usually spells GG if it lives another turn to start attacking or flinging projectiles. The incredible range of its first ability makes it a significant threat even to a well-protected avatar, and spawning foot soldiers when it dies makes it a bit more difficult for opponents to stabilize the board afterward. It's this added utility and the fact that it benefits from King of the Realm which led me to choose it over Conqueror Worm or Mountain Giant, though I suppose your mileage may vary.

Sites:

Bedrock gives you the most reliable source of mana and Earth affinity you could ask for. Its indestructible trait along with Geomancer's signature ability means you can reset the board by destroying Roots and recover your mana and threshold advantage very quickly, often creating a favorable board state that is very difficult for most opponents to overcome. It also gives you more of a fighting chance against Water decks since it can't be flooded or altered by cards like Atlantean Fate.

Common, Rustic Villages ensure you have a minion in play on the first turn in slightly less than half of all games, and can potentially flood the realm with a lot of cheap fodder in the form of foot soldiers if you play several of them consecutively. Foot Soldiers are Earth minions and mortals, so they can benefit from both Crusade and King of the Realm. These being ordinary sites also renders you less likely to be hosed by Atlantean Fate, which seems to be in every Water deck these days.

Free City is a stationary attacker/defender that costs nothing to cast and can't be destroyed by minions. It's a real life-saver against aggro decks using lots of small minions, and can even hold Battlemages in check with help from Cave-in and Dispel depriving them of their toys. An avatar sitting on one of these can be very difficult to harm without a concerted effort, so think of this site as a kind of card advantage engine, as it can potentially force the opponent to expend multiple resources trying to deal with this one card if you're using it effectively with your own spells and minions.

Gnome Hollows is a life-saver against any minion big enough to be a true threat to your avatar, making it an ideal first turn play to serve as an effective hideout in most games. The only reason I don't play three of them is because they can potentially create some awkward situations for your more powerful minions in late game.

Impenetrable Copse stops all projectiles from entering it from the outside, meaning that proper placement can keep your avatar and/or VIPs like Lady Iseult and King of the Realm safe from most common burn spells and obnoxious threats like Pudge Butcher, Nelly Long-arms and Grapple Shot. It's admittedly a situational filler card with just enough utility to warrant a full play set for now.

Mirror Realm does just about whatever you need it to. It can copy useful enemy sites if need be, or can serve as an extra copy of your more important sites like Free City, Gnome Hollows, Rift Valley, and Bedrock.

Pillar of Zeiros might actually be the only site you'd rather not draw early, as its utility is generally greater the longer the game goes on. It can save your life against burn strategies with massive life gain and makes for a great potential hoser against dedicated reanimator decks (Deathspeaker in particular). This site affects both cemeteries, so you might want to Rescue something before playing it.

Rift Valley is best used early and aggressively as a means of opening up another avenue of attack against the opponent's side of the board. It's not quite as powerful as Crusade, but it can serve well enough if played correctly. It gets harder to use effectively if drawn later when there are fewer voids on the board, but like Gnome Hollows, it still remains useful to hold as a pitch card for Craterize.

Roots of Yggdrasil serves essentially one purpose, which is to be destroyed if you are too far behind on board and need a reset button to buy time for a comeback. Geomancer's signature ability makes it easier to recover from this move than most other avatars because destroyed sites invariably turn into rubble. It's recommended to have at least one Bedrock in play when doing this, but it is not strictly necessary, again due to Geomancer's ability to rip sites from the top of your atlas and immediately start replacing the rubble around you.

Sinkhole serves as your main Roots enabler but can also be used to destroy enemy sites as needed. If drawn early without Roots, you can hold it until you find an actual use for it, or play it preemptively to restrict which sites your opponent may want to play in some situations.

Sideboard:

Commentary forthcoming for the day when I'm actually allowed to use it.

Snapple

@JMK